CA2824080A1 - Final beam transport system - Google Patents
Final beam transport system Download PDFInfo
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- CA2824080A1 CA2824080A1 CA2824080A CA2824080A CA2824080A1 CA 2824080 A1 CA2824080 A1 CA 2824080A1 CA 2824080 A CA2824080 A CA 2824080A CA 2824080 A CA2824080 A CA 2824080A CA 2824080 A1 CA2824080 A1 CA 2824080A1
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- optical element
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21B—FUSION REACTORS
- G21B1/00—Thermonuclear fusion reactors
- G21B1/11—Details
- G21B1/23—Optical systems, e.g. for irradiating targets, for heating plasma or for plasma diagnostics
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/10—Nuclear fusion reactors
Abstract
A system includes a laser system operable to provide a laser beam along an optical path and a fusion chamber coupled to the optical path. The system also includes a neutron pinhole disposed along the optical path between the laser system and the fusion chamber and a neutron attenuation region disposed along the optical path between the laser system and the fusion chamber.
Description
FINAL BEAM TRANSPORT SYSTEM
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent Application No.
61/437,177, filed on January 28, 2011, the disclosure of which is hereby incorporated by reference in its entirety.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional Patent Application No.
61/437,177, filed on January 28, 2011, the disclosure of which is hereby incorporated by reference in its entirety.
STATEMENT AS TO RIGHTS TO INVENTIONS MADE UNDER
FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] The United States Government has rights in this invention pursuant to Contract No.
DE-AC52-07NA27344 between the United States Department of Energy and Lawrence Livermore National Security, LLC, for the operation of Lawrence Livermore National Security.
BACKGROUND OF THE INVENTION
DE-AC52-07NA27344 between the United States Department of Energy and Lawrence Livermore National Security, LLC, for the operation of Lawrence Livermore National Security.
BACKGROUND OF THE INVENTION
[0003] Projections by the Energy Information Agency and current Intergovernmental Panel on Climate Change (IPCC) scenarios expect worldwide electric power demand to double from its current level of about 2 terawatts electrical power (TWe) to 4TWe by 2030, and could reach 8-10 TWe by 2100. They also expect that for the next 30 to 50 years, the bulk of the demand of electricity production will be provided by fossil fuels, typically coal and natural gas. Coal supplies 41% of the world's electric energy today, and is expected to supply 45% by 2030. In addition, the most recent report from the IPCC has placed the likelihood that man-made sources of CO2 emissions into the atmosphere are having a significant effect on the climate of planet earth at 90%. "Business as usual" baseline scenarios show that CO2 emissions could be almost two and a half times the current level by 2050. More than ever before, new technologies and alternative sources of energy are essential to meet the increasing energy demand in both the developed and the developing worlds, while attempting to stabilize and reduce the concentration of CO2 in the atmosphere and mitigate the concomitant climate change.
[0004] Nuclear energy, a non-carbon emitting energy source, has been a key component of the world's energy production since the 1950's, and currently accounts for about 16% of the world's electricity production, a fraction that could "in principle" be increased. Several factors, however, make its long-term sustainability difficult. These concerns include the risk of proliferation of nuclear materials and technologies resulting from the nuclear fuel cycle;
the generation of long-lived radioactive nuclear waste requiring burial in deep geological repositories; the current reliance on the once through, open nuclear fuel cycle; and the availability of low cost, low carbon footprint uranium ore. In the United States alone, nuclear reactors have already generated more than 55,000 metric tons (MT) of spent nuclear fuel (SNF). In the near future, we will have enough spent nuclear fuel to fill the Yucca Mountain geological waste repository to its legislated limit of 70,000 MT.
the generation of long-lived radioactive nuclear waste requiring burial in deep geological repositories; the current reliance on the once through, open nuclear fuel cycle; and the availability of low cost, low carbon footprint uranium ore. In the United States alone, nuclear reactors have already generated more than 55,000 metric tons (MT) of spent nuclear fuel (SNF). In the near future, we will have enough spent nuclear fuel to fill the Yucca Mountain geological waste repository to its legislated limit of 70,000 MT.
[0005] Fusion is an attractive energy option for future power generation, with two main approaches to fusion power plants now being developed. In a first approach, Inertial Confinement Fusion (ICF) uses lasers, heavy ion beams, or pulsed power to rapidly compress capsules containing a mixture of deuterium (D) and tritium (T). As the capsule radius decreases and the DT gas density and temperature increase, DT fusion reactions are initiated in a small spot in the center of the compressed capsule. These DT fusion reactions generate both alpha particles and 14.1 MeV neutrons. A fusion burn front propagates from the spot, generating significant energy gain. A second approach, Magnetic fusion energy (MFE) uses powerful magnetic fields to confine a DT plasma and to generate the conditions required to sustain a burning plasma and generate energy gain.
[0006] Important technology for ICF is being developed primarily at the National Ignition Facility (NIF) at Lawrence Livermore National Laboratory (LLNL), assignee of this invention, in Liveimore, California. There, a laser-based inertial confinement fusion project designed to achieve thermonuclear fusion ignition and burn utilizes laser energies of 1 to 1.3 MJ. Fusion yields of the order of 10 to 20 MJ are expected. Fusion yields in excess of 200 MJ are expected to be required in central hot spot fusion geometry if fusion technology, by itself, were to be used for cost effective power generation. Thus, significant technical challenges remain to achieve an economy powered by pure inertial confinement fusion energy.
SUMMARY OF THE INVENTION
SUMMARY OF THE INVENTION
[0007] According to embodiments of the present invention, methods and systems related to inertial confinement fusion are provided. More particularly a final optics beam transport system is provided that meets the top level requirements appropriate for a Laser Inertial Fusion Engine (LIFE) system. The optics enable fast pointing and transport of 351 nm light through dual neutron pinholes and focusing of the beam on target (e.g., a target tracking system employed with embodiments described herein will be capable of making shot pointing corrections in the last 301..ts before ignition). The optical system described herein enables a target tracking system and coaligned diagnostic beam. The final optics have been engineered to be robust to neutron damage and target shock pressure waves while providing minimal loss to the 351 nm laser beam. A method of replacing the final optics is also described.
Embodiments of the present invention are also applicable to other optical systems in a high radiation environment.
Embodiments of the present invention are also applicable to other optical systems in a high radiation environment.
[0008] According to an embodiment of the present invention, a method of replacing an optical element positioned in a high radiation environment is provided. The method includes halting operations of a beamline, pulling a cable to transfer the optical element through a radiation wall, and exchanging the optical element with a replacement optical element. The method also includes pulling the cable to transfer the replacement optical element through the radiation wall, positioning the replacement optical element adjacent the first end face of the telescope, and seating the replacement optical element on the first end face of the telescope.
The method further includes seating the replacement optical element on kinematic elements, verifying an optical alignment of the replacement optical element, and resuming operations of the beamline.
The method further includes seating the replacement optical element on kinematic elements, verifying an optical alignment of the replacement optical element, and resuming operations of the beamline.
[0009] According to another embodiment of the present invention, an optical system is provided. The optical system includes a chamber having a first end and a second end and an optic mount mounted to the first end of the vacuum chamber. The optic mount has a mounting surface. The optical system also includes a Fresnel optic mounted to the mounting surface and a cable attached to the optic mount. The optical system further includes a second optical element mounted to the second end of the vacuum chamber.
[0010] According to a particular embodiment of the present invention, a system is provided. The system includes a laser system operable to provide a laser beam along an optical path and a fusion chamber coupled to the optical path. The system also includes a neutron pinhole disposed along the optical path between the laser system and the fusion chamber and a neutron attenuation region disposed along the optical path between the laser system and the fusion chamber.
[0011] According to an embodiment of the present invention, a thin Fresnel optic is used as the final optic. The final optic (which may be fabricated in fused silica) is mounted in a frame that is sealed to a transport telescope containing a neutron pinhole (e.g., a large cement structure connected to the building) via a gasket (e.g., an 0-ring seal). In an embodiment, the aperture of the final optic is approximately 0.6 x 43 x 43 cm3 with an external pressure of 21 torr (2800 Pa) and an internal pressure of ¨0.5 mtorr. In this embodiment, approximately 116 pounds of force is present on the surface of the optic.
[0012] Embodiments of the present invention provide replaceable optics in an accessible manner without use of electronics, motors, hydraulics, or the like, which are unable to withstand a high radiation environment with an acceptable lifetime.
[0013] According to an embodiment of the present invention, a final optics beam transport system is provided that meets the top level requirements associated with high radiation environments found, for example, in LIFE. The optics allow slow pointing and transport of the 351 nm light through optically transparent neutron shielding (also referred to as neutron pinholes, which can be implemented in a dual pinhole configuration) and focus the beam on target. The final optics have been engineered to be robust to neutron damage and target shock pressure wave while providing reduced or minimal loss to the 351 nm laser beam. A
method of replacing these optics is provided by embodiments of the present invention.
method of replacing these optics is provided by embodiments of the present invention.
[0014] Numerous benefits are achieved by way of the present invention over conventional techniques. For example, embodiments of the present invention provide methods and systems that enable the replacement of optics in a region that is shielded from a neutron source by a shield wall. In some embodiments, the final optic used to focus laser light to a target provides for both focusing of light as well as a vacuum barrier and/or a tritium barrier.
These and other embodiments of the invention along with many of its advantages and features are described in more detail in conjunction with the text below and attached figures.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other embodiments of the invention along with many of its advantages and features are described in more detail in conjunction with the text below and attached figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a simplified schematic diagram illustrating elements of a final beam transport system according to an embodiment of the present invention;
[0016] FIG. 2 is a simplified schematic diagram illustrating a final beam transport system according to an embodiment of the present invention;
[0017] FIG. 3A is a schematic diagram illustrating a final beam transport system including two cascaded neutron pinholes according to an embodiment of the present invention;
[0018] FIG. 3B is a schematic diagram illustrating a final beam transport system including a single neutron pinhole according to an embodiment of the present invention;
[0019] FIG. 3C is a simplified schematic diagram illustrating elements of neutron pinhole telescopes according to an embodiment of the present invention;
[0020] FIG. 4A is a simplified plot of transmission in fused silica optics as a function of wavelength for a set of annealing conditions;
[0021] FIG. 4B is a simplified plot of the absorption in fused silica optics as a function of temperature;
[0022] FIG. 5 is a simplified graph illustrating a shock pressure wavefolin incident on the final optic according to an embodiment of the present invention;
[0023] FIG. 6A is a contour plot illustrating induced stress in the final optic from the target ignition shock;
[0024] FIG. 6B is a contour plot illustrating the maximum displacement of the final optic from target ignition shock;
[0025] FIG. 7A is a simplified schematic diagram of a final optic changeout system according to an embodiment of the present invention;
[0026] FIG. 7B is a simplified schematic diagram of an optical pass-thru for final optic replacement including a labyrinth neutronics barrier in a shield wall according to an embodiment of the present invention;
[0027] Fig. 8A is a simplified schematic diagram illustrating a system for mechanical mounting repeatability and vacuum capability according to an embodiment of the present invention;
[0028] FIG. 8B is a simplified schematic diagram illustrating a system including independent removability of window modules from any pair in the system according to an embodiment of the present invention;
[0029] FIG. 8C is a simplified flowchart illustrating a method of exchanging a final optic in a high radiation environment according to an embodiment of the present invention;
[0030] FIG. 9A is a simplified schematic diagram illustrating a laser bay labyrinth maintenance entrance to area between shield walls according to an embodiment of the present invention;
[0031] FIG. 9B is a simplified schematic diagram illustrating a laser bay labyrinth and neutron pinhole architecture according to an alternative embodiment of the present invention;
[0032] FIG. 10 is a diagram illustrating the evolution of the environment near target chamber center as a function of time according to an embodiment of the present invention;
[0033] FIG. 11A is a simplified graph illustrating laser transmission as a function of distance from the laser entrance hole due to inverse Bremstrahlung absorption according to an embodiment of the present invention; and [0034] FIG. 11B is a simplified graph illustrating saturation of the SRS
signal in lead vapor according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
signal in lead vapor according to an embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Embodiments of the present invention relate to fusion reaction chambers.
Embodiments of the present invention are applicable to energy systems including , but are not limited to, a Laser Inertial-confinement Fusion Energy (LIFE) engine, hybrid fusion-fission systems such as a hybrid fusion-fission LIFE system, a generation IV reactor, an integral fast reactor, magnetic confinement fusion energy (MFE) systems, accelerator driven systems and others. In some embodiments, the energy system is a hybrid version of the LIFE
engine, a hybrid fusion-fission LIFE system, such as described in International Patent Application No.
PCT/US2008/011335, filed September 30, 2008, titled "Control of a Laser Inertial Confinement Fusion-Fission Power Plant", the disclosure of which is hereby incorporated by reference in its entirety for all purposes.
Embodiments of the present invention are applicable to energy systems including , but are not limited to, a Laser Inertial-confinement Fusion Energy (LIFE) engine, hybrid fusion-fission systems such as a hybrid fusion-fission LIFE system, a generation IV reactor, an integral fast reactor, magnetic confinement fusion energy (MFE) systems, accelerator driven systems and others. In some embodiments, the energy system is a hybrid version of the LIFE
engine, a hybrid fusion-fission LIFE system, such as described in International Patent Application No.
PCT/US2008/011335, filed September 30, 2008, titled "Control of a Laser Inertial Confinement Fusion-Fission Power Plant", the disclosure of which is hereby incorporated by reference in its entirety for all purposes.
[0036] Embodiments of the present invention provide for protection of system elements from neutron fluence, which can potentially limit the lifetime of the optics.
One of the optics at high risk is the final optic, which withstands all of the issues described in Table 1 in addition to the laser energy. The final optic is directly exposed to the gases from the target chamber (primarily xenon, but with target admixture of helium, hydrogen, deuterium, tritium, lead, carbon) and target shrapnel. For some commercial power plants utilizing LIFE designs, the baseline output power is 1950 MW. The ions and x-rays are absorbed by the xenon gas in the target chamber, leaving 1560 MW of 14 MeV neutrons from the fusion reaction which yield an average exposure of 1.5x1017 n/m2-sec at the final optic location. In addition, there is a pressure wave producing ¨ 0.53 torr of pressure at the final optic location in addition to the baseline pressure of 21 ton. Finally, the optic is positioned in an environment coupled to the vibrations associated with the gas expansion from ignition and liquid lithium flow in the target chamber blanket. This is somewhat mitigated in some LIFE designs by mechanically decoupling the first wall and blanket from the vacuum chamber that is connected to the optical pipe assembly. The beamline apertures in the blanket also act to attenuate the gas shock incident on the final optic. The final optic is designed to survive the residual threat and efficiently transmit and focus the 351 nm laser light at ¨3 J/cm2 (noiinal to the beam).
Target Quantity* Nature of the Threat How it is Handled Emission Atomic displacement Thermal annealing and /second Neutrons= 2 x 1013 n/cm2-s damage & nuclear design optic to be transmutation tolerant Charged ¨10% = 280 MW in Ion displacement, Stop ions in sputtering, surface particles ¨60keV Maxwellian chamber gas heating / ablation ¨12% = 340 MW Surface heating & Attenuated (stopped) in X-rayschamber gas and beam = 0.5 J/cm2 15Hz ablation tubes Thermal annealing and Gamma- Breakage of chemical <1% design optic to be rays bonds tolerant Over-pressure of ¨4 kPaMechanical design of Gas Mechanical stress to final for 5-10 ms (20-40 kPa-optics and/or counter gas shocks optic s) flows Table 1. Final optic threats 5 [0037] The final beam transport system includes the optics utilized to transport the beam from the exit of the frequency converter to the target chamber center. The final optic system is robust, serviceable, delivers the laser through optically transparent neutron shielding (also referred to as neutron pinholes since laser light is able to propagate through the pinholes without substantial optical losses), and survives multiple threats from the target chamber.
10 Referring to FIG. 2, this final beam transport system includes optic M10 and all following optics. In addition to the laser fluence at 351 nm, L11, LG1 and FL1 are exposed to neutron irradiation, and FL1, the final optic, is exposed to additional mechanical shock and target shrapnel from target ignition. The final optics transport shown schematically in FIG. 2, differs from the NIF architecture, which utilizes a wedged focusing lens and debris shield installed in close proximity to the frequency converter. To protect the laser system and operations personnel from neutron irradiation, devices called neutron pinholes are used. The neutron pinhole is a small (¨ lcm) hole in three meter thick concrete shield walls which allow light to pass, but absorbs most of the neutrons escaping the target chamber.
If this pinhole is situated at the focal location of a Galilean relay telescope, the aperture of this pinhole can be minimized (theoretically to the same size as pinholes in the le) beamline) thereby minimizing transmitted neutrons while fully transmitting the laser light.
[0038] FIG. 3A is a schematic diagram illustrating a final beam transport system including two cascaded neutron pinholes according to an embodiment of the present invention.
Although the system can be referred to a "two neutron pinhole" system, it will be understood that the system utilizes two sets of neutron pinholes. Systems designed as illustrated in FIG.
3A experience a radiation dose that is attenuated to 0.04 rem/year utilizing two cascaded neutron pinholes. It should be noted that the final optic 326/320 not only focuses, but deflects the beam from the axis of the second neutron pinhole relay telescope (including focus lens 314 and Fresnel lens (type 2a) 316 and matching focus lens 315 /
Fresnel lens 318 to the target chamber center 386. Since the final optic (i.e., Fresnel lens (type 2b) 326 and matching final optic (i.e., Fresnel lens (type 1 b) 320 deflects the laser beam, it only acts as a scattering source for neutrons, thereby preventing ballistic neutrons from passing through the neutron pinhole at location. The transmitted spectrum of neutrons from the pinhole 330 will be a roughly collimated beam of neutrons that have scattered from the surrounding shield materials and blanket after some collimation by the pinhole structure. As shown in FIG. 3A, the axis of the second neutron pinhole at location 332 is again deflected from axis of the first neutron pinhole at location 330, which prevents ballistic neutrons from the second pinhole from passing through the first one. Using this technique, the neutron dosage can be attenuated to levels such that human occupation of the laser bay is possible.
[0039] In an embodiment, the laser bays 310A and 310B include 2.2 m wide x 1.35 m high x 10.4 m long lw lasers/amplifiers. These laser bays are able to produce laser beams with 435 mm square beam dimensions suitable for fusion applications. Additionally, in some embodiments, the inner cone 324 is characterized by an angle of 26.9 and the outer cone 322 is characterized by an angle of 47.25 , but these particular angles are not required by the present invention. As an example, in other embodiments, the cone angles are 30 and 50 .
[0040] The optical design of the final transport optical system meets many requirements simultaneously, including: the ability to point and center to incoming targets at the target chamber center, efficient transport of the 351 nm light to target chamber center, and focus of the energy into the Laser Entrance Hole (LEH) of the target hohlraum. To achieve these ends, the mirrors M10 and M1 1 shown in FIG. I are used to maintain centering on the final transport optics and slow pointing to the target. The lenses L9, L10, and L11 in addition to transporting the beam through the first neutron pinhole, also serve to null out the chromatic dispersion induced by the Fresnel final optic, which has the opposite sign relative to traditional convex lenses. The grating LG1 compensates for the temporal skew induced by the deflection (diffraction) of the Fresnel final optic and also serves to provide the deflection required between neutron pinhole 1 and 2. Thus fully compensated both chromatically and temporally, the Fresnel optic can focus the 351 nm drive laser beam into the LEH of the target.
[0041] Embodiments of the present invention utilize one of several optical elements as the final optic including: a grazing incidence metal mirror (GIMM), an elliptic mirror, a thin Fresnel optic, or the like. In embodiments utilizing a GIMM or parabolic mirror, an additional vacuum window is included in the design upstream (e.g., immediately) of the final optic before the neutron spatial filter. This optic serves two purposes among others: to guarantee vacuum at the telescope focus so that the laser light can be transmitted, and to serve as a tritium barrier. The Fresnel optic illustrated in FIG. 1 acts as both the final focusing optic and as the vacuum barrier. By making this final optic thin, the neutron induced absorption can be reduced to level of a few percent.
[0042] Although the angle between the optical axes of the two relay telescopes associated with the neutron pinholes is angled at an angle of about 60 , this is not required by the present invention and other embodiments utilized different angles between telescopes. In some embodiments, the first relay telescope is oriented in a horizontal plane and the second relay telescope is oriented in a vertical plane, with a right angle between the two optical axes.
Other orientations are included within the scope of the present invention in addition to those illustrated. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.
[0043] FIG. 3B is a schematic diagram illustrating a final beam transport system including a single neutron pinhole according to an embodiment of the present invention.
Referring to FIG. 3B, laser sources 350A through 350N are provided in a first region 351.
Light from the laser sources 350A through 350N is directed toward a shield wall 352, for example, a all 3 m in thickness. A set of neutron pinholes 353A through 353N are provided in the shield wall 352 to enable the laser radiation to pass through the shield wall after focusing using a set of optical system (e.g., a set of N relay telescopes). Thus, when this system is referred to as a "single neutron pinhole" system, this can be understood as utilizing a single set of neutron pinholes rather than two sets of neutron pinholes.
[0044] Light passing through the set of neutron pinholes 353A through 353N
reflects off parabolic mirrors 360 in the illustrated embodiment to impinge on Fresnel optics 362 and 364. In some embodiments, the distance between Fresnel optics 326 and 364 is sufficient to enable parabolic mirrors 360 to be positioned under ledge 361. After focusing by Fresnel optic 364, light is focused onto target 386.
[0045] Neutrons generated at the target 386 propagate out in all directions including cone 368, passing through the space between walls 366 and 365. Neutrons to the left of cone 368 are reflected or absorbed by wall 366. In an embodiment, wall 363 and ledge 361 define the angular spread of cone 368. Although the neutrons impinge on Fresnel optic 364, wall 365 prevents neutrons from impinging on Fresnel optic 362. Because the neutrons are contained between wall 363 and ledge 361, only a single set of neutron pinholes is needed to reduce the neutron density in region 351 to acceptable levels.
[0046] FIG. 3C is a simplified schematic diagram illustrating elements of neutron pinhole telescopes according to an embodiment of the present invention. As illustrated in FIG. 3C, a first telescope 370 focuses light through the secondary shield wall 372 to pass through a second neutron pinhole 374. The light is refracted through Fresnel optic 376A, which forms an element of a second relay telescope 370. The second relay telescope 380 focuses light through the primary shield wall (not shown) to pass through a first neutron pinhole at location 382A. As is evident by the figure, multiple, parallel light paths are provided by embodiments of the present invention, providing multiple neutron pinholes passing through the primary and secondary shield walls as illustrated by neutron pinhole 374B, light from which is collected by Fresnel optic 376B.
[0047] Light passing through the first neutron pinhole at location 382 is incident on Fresnel optic 384A, which collects and focuses the light onto the target 386. Because both grating structures present in Fresnel optics 376A and 384A receive light from a point source and focus light to a corresponding point source, the manufacturing of these Fresnel optics is simplified, enabling a high quality manufacturing process to be utilized. In order to manufacture these gratings, a point source is utilized to define the grating structures since light passing through the gratings originates and terminates as a point source. As illustrated, the gratings are receiving divergent light and producing convergence of the received light.
Thus, grating exposure can be accomplished using point sources. Various cone angles can be utilized according to embodiments of the present invention, for example, an angle of 26.9 for the inner cone between the target 386 and Fresnel optic 384A and an angle of 47.2 for the outer cone between the target 386 and Fresnel optic 384B.
[0048] According to some embodiments, the manufacturing process is improved in comparison to other architectures since point sources can be utilized in the grating definition process. As an example, Fresnel optics manufactured for use in embodiments as illustrated in FIG. 3C have reduced aberrations in comparison with Fresnel optics in which a divergent beam is collimated.
[0049] The inventors note that the neutron-induced absorption in fused silica saturates at fairly modest neutron irradiation levels, and this absorption can be partially annealed by raising the temperature of the substrate as illustrated in FIG. 4A. In an embodiment, a 5.3 mm thick fused silica substrate is utilized for the Fresnel optic, which is sufficient to serve as the vacuum barrier between the target chamber at 21 ton and the relay telescope at approximately 0.5 mtorr.
[0050] The inventors have determined that if an optic of sufficient thickness (e.g., a 5.3 mm thick optic) is maintained at ¨580 C, the absorption loss is reduced to ¨
0.5%. As illustrated in FIG. 4B, the absorption of fused silica optics varies as a function of temperature. The heating can be accomplished through use of beam heating, an external heater producing ¨3.4 MW, or a combination thereof. In embodiments in which no heater is used, the inventors have detennined that beam heating alone will raise the temperature of the optic to ¨518 C, with an associated transmission loss of 3.5%, which is suitable for some applications.
According to an embodiment of the present invention, a 5.3 mm thick fused silica Fresnel optic is utilized for the final optic, although embodiments of the present invention are not limited to this particular thickness. Other thicknesses can also be utilized.
[0051] FIG. 4A is a graph illustrating corrected transmission percentage as a function of wavelength for a final optic according to an embodiment of the present invention. FIG. 4B is a graph illustrating laser absorption versus temperature for a 5.3 mm thick fused silica optic.
[0052] Referring to FIG. 4A, the annealing processing of neutron damaged silica demonstrates a large change in 351 nm transmission as a result of the annealing process.
[0053] In addition to the neutron threat, a shock wave generated by the target ignition will be incident on the final optic. FIG. 5 is a simplified graph illustrating a shock pressure waveform incident on the final optic according to an embodiment of the present invention.
FIG. 6A is a contour plot illustrating induced stress in the final optic from the target ignition shock. FIG. 6B is a contour plot illustrating the maximum displacement of the final optic from target ignition shock. As illustrated in FIGS. 6A and 6B, there is about 2 um of displacement in the final optic and about 40,000 Pascals of stress, which is acceptable for the designs described herein.
100541 This optic can be mounted in a frame that can be sealed using a gasket seal to a transport telescope containing a neutron pinhole, which is a large cement structure connected to the building. In an embodiment, the aperture of the fused silica optic is approximately 0.53 x 43 x 49.65 cm3 (43cm aperture at angle of 30 ) with an external pressure of 21 ton (2800 Pa) and an internal pressure of 0.5 mtorr, which results in 134 pounds of force on the surface of the optic. An additional 0.5 ton (70 Pa) is incident on the final optic during the ¨135 jis shock pulse as shown in FIG. 5. To understand the mechanical effect of this impulse on the 5.3 mm thick optic, a model was built in quarter symmetry using a Shells model (a finite element gridding technique useful for thin substrates). For boundary conditions, the contact points to the gasket were modeled as knife edge rollers (supported normal to the optic only).
The first modal frequency is 131 Hz. The induced stress and displacement of the optic due to the impulse are shown in FIG. 6. The maximum effective surface stress is 40600 Pa. The maximum displacement is 2.62x10-6 m (2.62 m). Both the maximum displacement and maximum effective surface stress occur at approximately 6 ms into the analysis. These results indicate the final optic survival is not threatened by the shockwave, and the maximum surface displacement should not have a significant impact on the laser focal spot. It should be noted that mounting of the final optic can be designed to avoid resonance at the modal frequency or induced vibration from the building due to the previous shot and/or support equipment fluid flow (e.g., blankets, cooling, or the like). Engineering of passive damping mechanisms for the vibration can be performed based on the spectrum for this final optic including effects based on the chamber environment and the mechanical mounting hardware design.
[0055] As illustrated in FIG. 6A, the global maximum effective surface stress is 4.06 x 104 with a global minimum of zero. As illustrated in FIG. 6B, the global maximum displacement of the final optic is 2.62 x 10-6 m and the global minimum displacement is -2.47 x 10-6.
These values are not intended to limit embodiments of the present invention but to provide examples of the stress and displacement encountered in various embodiments of the present invention.
[0056] Embodiments of the present invention provide methods and systems for replacement of the final optic (as well as other optics between the two neutron pinholes) in a radiation hot environment. To first order, no electronics are able to survive in this environment and would have a low MTTF. The replacement hardware will have a very large MTTF, since failure of these components would require plant shut-down (affecting plant availability) to enable access to the hardware in the high radiation area around the target chamber.
[0057] FIG. 7A is a simplified schematic diagram of a final optic changeout system according to an embodiment of the present invention. The system illustrated in FIG. 7A
provides a dual optic replacement capability and simple mechanical replacement via a cable drive 720 into the high radiation area. FIG. 7B is a simplified schematic diagram of an optical pass-thru for final optic replacement including a labyrinth neutronics barrier in a shield wall according to an embodiment of the present invention. Some embodiments of the present invention are enabled by the geometry of the Fresnel optic, for example, 40 cm or 50 on a side, but only 5 mm thick and the associated low weight. The thin nature of the Fresnel optic 705 additionally enables removal through a thin labyrinth 730 as illustrated in FIG. 7B.
[0058] As illustrated in FIG. 7A, a system for replacement of the thin Fresnel optic 705 is provided that does not utilize any hydraulic or motorized devices in the high radiation area.
As illustrated in FIGS. 7A and 7B, this system and method uses cables with pulleys or rollers to guide damaged Fresnel lenses out of the high radiation environment through curved slits in the shield wall that serve as neutron labyrinths but allow exchange of the final optic. A close-up of one of these labyrinths is shown in FIG. 7B with dimensions that are used in an exemplary embodiment suitable for neutronics modeling.
[0059] Referring to FIG. 7B, optical assemblies pass through a labyrinth to prevent the neutrons from passing through the wall associated with the passage of the optical assemblies.
As illustrated in FIG. 1, the neutron pinholes provided for passage of the laser beams are oriented at an angle with respect to each other to prevent neutrons passing through the innermost pinhole as undeflected neutrons. The optical assemblies are able to pass through the labyrinth, which blocks neutrons as a function of the shape of the labyrinth. Referring to FIG. 7B, in some embodiments, the labyrinth has a width of 15 cm and a radius of curvature of ¨150 cm, providing a distance between entrance and exit ports of 300 cm for a 300 cm thick wall.
[0060] Although not illustrated in FIG. 7A for purposes of clarity, embodiments of the present invention utilize two cable systems (one for each Fresnel optic 705) with a cable attached at the top and bottom of each optic (i.e., 4 cables total running through the two labyrinthine slits in the wall). In other embodiments, other implementations can be utilized.
As illustrated in FIG. 7A, arrow 702A illustrates the movement of the left-hand optic during replacement and arrow 702B illustrates the movement of the right-hand optic during replacement.
[0061] Although the labyrinth illustrated in FIG. 7B is a continuous curved structure, this is not required by embodiments of the present invention. In other embodiments, a zig-zag labyrinth as shown in FIG. 7C is utilized.
[0062] Since, in some embodiments, there is no adjustment capability in the final optics, the mounting hardware enables precision kinematic replacement. This is achieved in the illustrated embodiment by creating a telescope end face 805 as shown in FIG.
8A, where ferromagnetic steel balls 825 (e.g., Nd-based magnets or other high strength to mass ratio magnets such as neodymium iron boron-based magnets, samarium cobalt-based magnets, or other similar magnets) are mounted into the surface to provide kinematic registration points 827 for the Fresnel optic module, also shown in FIG. 8A. In other embodiments, the kinematic mounts are reversed, with the magnets and kinematic registration points provided on the opposing elements (i.e., magnets mounted on the LRU and registration points on the telescope end face). As illustrated in FIG. 8A, the Nd-based high power magnets (which may be replaced with other suitable high strength to mass ratio magnets), the Fresnel optic, and vacuum gasket 830, are all mounted together on the final optic frame 807 that is a line replaceable unit. The precision frame can be fabricated from a rigid material such as stainless steel with cable attachments 840. To enable independent removal of window modules, two pairs of cable drives are provided as shown in the front view illustrated in FIG. 8B.
[0063] Referring to FIG. 8A, the end of the telescope includes a steel flange including kinematic nodules 825 on the end that are also made out of steel. The use of steel enables the elements illustrated in FIG. 8A to possess a lifetime similar to other chamber elements.
Elements that are replaceable are mounted to the steel flange, for example, the final optic 815 (e.g., the fused silica Fresnel lens, which can be mounted offline to provide micro-alignment capabilities), the gasket 830 for creating a vacuum seal at the surface, the Nd-based magnets 827, the attachments 830 for cabling, which is used to move the assembly into and out of the system during replacement and repair operations, and the like. In some embodiments, two assemblies are provided side-by-side and the left hand one would changed out to the left and the right hand one would get changed out to the right using two independent cabling systems.
As illustrated in FIG. 8B, independent cable pairs 852 and 854 enable allow window modules on both sides to be independently removable. In some implementations, the gasket is optional since some embodiments do not utilize a vacuum environment for portions of the system. In these embodiments, the optics can be mounted, but not sealed to a neutron pinhole, with no pressure differential present across the optic. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.
100641 FIG. 8C is a simplified flowchart illustrating a method of exchanging a final optic in a high radiation environment according to an embodiment of the present invention. The method 800 includes halting operations (810), optionally venting the telescope to chamber pressure (812), and optionally adding additional Xe gas to "burp" the lens from the telescope end face (814). The method also includes pulling the cable to retrieve the final optic through radiation wall (816), and exchanging the final optic using robotics in the region between neutron pinhole #1 and neutron pinhole #2 (818). The method further includes pulling the cable to position the replacement final optic in front of telescope end face (820), using the magnets to pulls the final optic into kinematic position (822), optionally pulling a vacuum to seat the final optic on kinematics (824), verifying the alignment and repointing the beam as necessary (826), and resuming operations (828). Although kinematics are utilized in the illustrated embodiment, this is not required by embodiments of the present invention and other alignment techniques are included within the scope of the present invention.
100651 It should be appreciated that the specific steps illustrated in FIG. 8C
provide a particular method of exchanging a final optic in a high radiation environment according to an embodiment of the present invention. Other sequences of steps may also be performed according to alternative embodiments. For example, alternative embodiments of the present invention may perform the steps outlined above in a different order. Moreover, the individual steps illustrated in FIG. 8C may include multiple sub-steps that may be performed in various sequences as appropriate to the individual step. Furthermore, additional steps may be added or removed depending on the particular applications. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.
100661 Although a particular method of sealing optics is provided in relation to FIG. 8C, embodiments of the present invention are not limited to these approaches. In other embodiments, a push-pull seal is utilized as a valve, similar to a canister's seal. Thus, embodiments of the present invention provide for seal creation at a distance by venting one side of a valve and then changing out the optic. By actuating a lever, a seal can be created as the optical mount is urged against a flange. In order to release the seal, the lever is actuated in an opposing direction to enable the optical mount to move away from the flange in a manner analogous to a canister lid. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.
[0067] The method illustrated in FIG. 8C allows the passive method of magnetic kinematic mounting to maintain alignment across multiple servicing operations. All expendable components can be readily removed from the high radiation environment without shutting down the power plant for direct maintenance. All required pneumatic vacuum valves, motorized cable drive, and robotic optic exchange have been limited to the area between neutron pinhole #1 and #2. This area and access are schematically shown in FIG. 9A. An airlock door 920 which provides both vacuum and tritium barrier is located in an entrance of labyrinth 940, which keeps the laser bay radiation levels safe for personnel.
Robotic service vehicles 930 can enter supplying new materials (optics and/or hardware) to replace components. These same vehicles can be used to carry used components in shielded containers to radiation hazardous waste locations in the plant for recycling and/or disposal.
As illustrated in FIG. 9A, after the final optic is removed through the labyrinth into the lower radiation area 911, a vehicle is able to remove the optic through an interlock.
[0068] Embodiments of the present invention operate such that the pressure of this environment is low (-21 torr), which will prevent all but the lightest of particulates from remaining suspended in the chamber gas and thereby promote cleanliness. Gas purge nozzles can be located in the region of the final optic with their ultimate purpose being both to provide counter flow pressure to offset the "puffs" of chamber gas from target ignition and also to provide a low pressure "air knife" to clean the final optic as it is being replaced and maintain that cleanliness during operations. Control of this purge flow rate can be done using pneumatic valves located in low radiation areas outside of the primary shield wall. During maintenance operations this purge pressure can be briefly increased to enable gas cleaning of the final optic to meet requirements.
[0069] In addition to the systems to provide for long lived and replaceable final optics, embodiments of the present invention address concerns for the optics located between the neutron These optics (L11 and LG1 as illustrated in FIG. 9) and their associated hardware are in a radiation environment that compounds the threat to the optic and limits access and maintenance capabilities. Initial neutronics calculations show the neutron pinhole #2 (pinhole 925 in the primary shield wall 926) attenuating the 1.5 x 1017 n/m2 sec incident dosage significantly. These neutrons appear to be highly collimated, which will enable relatively simple neutron dumps to be used to limit the neutron flux in the area between the neutron pinholes. Motorized vehicles 930 and actuators with electronics will be allowed into this area for servicing and some components may be allowed permanent occupation in this area. Servicing of optics already in this area is much more straightforward and can be accomplished with handling methods commensurate with standard cleanliness protocols.
[0070] FIG. 9B is a simplified schematic diagram illustrating a laser bay labyrinth and neutron pinhole architecture according to an alternative embodiment of the present invention.
As illustrated in FIG. 9B, an architecture is provided that provides neutron shielding using a single set of neutron pinholes (e.g., the set of four neutron pinholes 950 shown in FIG. 9B).
[0071] Laser/amplifiers are provided in the laser bay 955, which is at atmospheric pressure and utilizes an air environment in the illustrated implementation. Light from the lasers/amplifiers is directed, using optics, to pass through the shield wall 952 including the single set of neutron pinholes 950. Utilizing other optics as illustrated, the laser beams, after passing through the set of neutron pinholes, are directed in a zig-zag manner around walls 956 and 958 to impinge on the target chamber 960. In the illustrated implementation, the target chamber 960 is at 21 torr, with a mixture of xenon and tritium, produced as a consequence of the fusion reactions. The labyrinth area 962 is at substantially the same atmospheric conditions as the target chamber, 21 ton with a mixture of Xe and T. Neutrons produced in the target chamber 960 that are propagating toward the labyrinth area 962 are blocked by walls 958 and 956 and are, therefore, not able to reach the neutron pinholes in substantial densities.
[0072] In order to replace optics, including the final optic 970, a cable/rail guided system 980 is provided to enable removal and replacement of optics as described more fully throughout the present specification. After their useful life, optics are removed using the cable/rail guide system 980 as they are routed along shield wall 982 and extracted through an airlock door 984, which also serves as a tritium barrier. After extraction through the airlock door 984, robotic optics replacement vehicles 990 can be used to remove spent optics and deliver new optics. The environment for the robotic optics replacement vehicles can be atmospheric pressure, for example, air.
[0073] Referring once again to FIG. 1, the final beam transport system provides a mechanism to direct the 351 nm laser light to the target chamber center. In contrast with some other fusion technology systems (e.g., NIF), the chamber is not at hard vacuum. In some embodiments, the chamber is intentionally filled with a protection mechanism, such as xenon gas at 4 g/cm3, to protect the chamber walls from ions and x-rays.
Target ignition at 15 Hz adds components of the target (hydrogen, deuterium, tritium, helium, carbon, lead, and the like) to this gas mixture as well since the vacuum system doe not typically replace all of the gas before the next shot. Therefore, a detailed analysis of the beam propagation through this complex gas mix has been performed to provide information related to the beam dynamics (e.g., filamentation or scattering due to nonlinear processes). The analysis begins by in one implementation by propagating the 2TW, 15 ns, laser beam at 0.351 tm through tens of cm of Xe/Pb plasma near target chamber center and meters of gas starting at the final optic. The generation and evolution of this target chamber environment is illustrated in FIG.
10.
[0074] Referring to FIG. 10, prior to the laser shot, the gas is at a non-ionized state with a 5% lead mixture at ¨ 0.5 eV. As the foot of the laser pulse begins to heat the target, a plasma ball farms that grows to an extent of 25 cm during the laser pulse. After ¨ 1 lis, the plasma has radiatively cooled to a hot mix of neutral gas, which continues to radiate until the next target shot.
[0075] The interactions of the laser with the gas and the expanding plasma are given in Table 2, where the interactions are characterized by type and an assessment of the effect on the beam is given. Most of the effects are well understood and will depend on the actual target gas mix and temperature environment. It should be noted that the primary loss mechanisms for the beam appears to be the ionized gas in the plasma ball surrounding the target. This transmission loss as a function of distance from the target is shown in FIG. 11A, and induces a negligible loss of 0.5% at 351 nm. In an extreme case in which the entire chamber were to remain ionized, the loss would only increase to 1.5% for the 61.tg/cm3 case.
The second loss mechanism of interest is Stimulated Raman Scattering from the lead gas from the target hohlraum. Electronic Stimulated Raman Scattering (scattering from bound electrons) has been extensively studied with dye laser in heat pipes (alkali vapors) in the past.
Conversion efficiency > 60 % was observed for Pb vapors around 1 ton. The inventors have determined that the intensity - length product for a LIFE beamlet is so large that the relevant gain exponent will reach 10X threshold (G ¨ 30) after the 1 ns of the laser impulsion. This will result in full saturation of the SRS medium.
[0076] Referring to FIG. 11B, lmJ of SRS @0.02 Ton corresponds to ¨ 1 photon per atom. Therefore, if all of the available lead atoms that are in the laser illumination volume in the target area are excited, this corresponds to ¨ 20 kJ for the entire LIFE
laser system (all beams), which would be equivalent to doubling the energy of the first "picket"
on the laser pulse shape. The SRS loss corresponds to a beamline loss of 0.83%. Based on these values, the apparent loss to the incoming beams is very reasonable ¨1.33 ¨
2.33% for all affects at the 6 p,g/cm3 case discussed herein. It should be noted that the previous analysis does not include the last centimeter of propagation (near the hohlraum LEH) where the beams begin to overlap, which is addressed by energetics analysis.
Interaction Assessment Laser- Inverse Bremstrahlung (photons less than 50 cm of beam path is ionized plasma absorbed by free electrons) and calculated I. B.
absorption is 0.5%
(free @ 6 [ig/cc Xe and 1.5 % @ 8 g/cm3 electrons) Xe Stimulated Brillouin scattering Gsbs <1 for a beamlet due to low (photons scattered by ion-acoustic density/low intensity waves) Stimulated Raman scattering (photon Gsrs < 1 for a beamlet due to low scattered by "free" electron plasma density/low intensity waves) Ponderomotive filamentation G << 1 (nonlinear plasma refraction) Laser- Raman scattering from bound not a problem for Xe/Xe; Pb debris gas/vapor electrons requires doubling the first picket energy (bound to saturate the medium (20 kJ) electrons) B-integral (index of refraction B-integral <0.1 radian for a beamlet; no nonlinear with intensity; Kerr effect) filamentation Refraction through a density gradient a 40 jig/cm3 cold Xe jet leads to a 301.im (beam deflection) / turbulence mispointing at 5m; turbulence likely not an issue Break down in Xe gas along the path breakdown threshold in Xe gas is to TCC reached ¨ 50 cm from TCC at peak power (11ns), while plasma ball radius is <25 cm, but density too low for cascading/self-focusing interaction with Xe droplets; Pb2 unlikely in 0.5 eV Xe/Pb gas dimers (Rayleigh scattering; break down; absorption) Table 2. Laser focal interactions with target gas [0077] It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.
One of the optics at high risk is the final optic, which withstands all of the issues described in Table 1 in addition to the laser energy. The final optic is directly exposed to the gases from the target chamber (primarily xenon, but with target admixture of helium, hydrogen, deuterium, tritium, lead, carbon) and target shrapnel. For some commercial power plants utilizing LIFE designs, the baseline output power is 1950 MW. The ions and x-rays are absorbed by the xenon gas in the target chamber, leaving 1560 MW of 14 MeV neutrons from the fusion reaction which yield an average exposure of 1.5x1017 n/m2-sec at the final optic location. In addition, there is a pressure wave producing ¨ 0.53 torr of pressure at the final optic location in addition to the baseline pressure of 21 ton. Finally, the optic is positioned in an environment coupled to the vibrations associated with the gas expansion from ignition and liquid lithium flow in the target chamber blanket. This is somewhat mitigated in some LIFE designs by mechanically decoupling the first wall and blanket from the vacuum chamber that is connected to the optical pipe assembly. The beamline apertures in the blanket also act to attenuate the gas shock incident on the final optic. The final optic is designed to survive the residual threat and efficiently transmit and focus the 351 nm laser light at ¨3 J/cm2 (noiinal to the beam).
Target Quantity* Nature of the Threat How it is Handled Emission Atomic displacement Thermal annealing and /second Neutrons= 2 x 1013 n/cm2-s damage & nuclear design optic to be transmutation tolerant Charged ¨10% = 280 MW in Ion displacement, Stop ions in sputtering, surface particles ¨60keV Maxwellian chamber gas heating / ablation ¨12% = 340 MW Surface heating & Attenuated (stopped) in X-rayschamber gas and beam = 0.5 J/cm2 15Hz ablation tubes Thermal annealing and Gamma- Breakage of chemical <1% design optic to be rays bonds tolerant Over-pressure of ¨4 kPaMechanical design of Gas Mechanical stress to final for 5-10 ms (20-40 kPa-optics and/or counter gas shocks optic s) flows Table 1. Final optic threats 5 [0037] The final beam transport system includes the optics utilized to transport the beam from the exit of the frequency converter to the target chamber center. The final optic system is robust, serviceable, delivers the laser through optically transparent neutron shielding (also referred to as neutron pinholes since laser light is able to propagate through the pinholes without substantial optical losses), and survives multiple threats from the target chamber.
10 Referring to FIG. 2, this final beam transport system includes optic M10 and all following optics. In addition to the laser fluence at 351 nm, L11, LG1 and FL1 are exposed to neutron irradiation, and FL1, the final optic, is exposed to additional mechanical shock and target shrapnel from target ignition. The final optics transport shown schematically in FIG. 2, differs from the NIF architecture, which utilizes a wedged focusing lens and debris shield installed in close proximity to the frequency converter. To protect the laser system and operations personnel from neutron irradiation, devices called neutron pinholes are used. The neutron pinhole is a small (¨ lcm) hole in three meter thick concrete shield walls which allow light to pass, but absorbs most of the neutrons escaping the target chamber.
If this pinhole is situated at the focal location of a Galilean relay telescope, the aperture of this pinhole can be minimized (theoretically to the same size as pinholes in the le) beamline) thereby minimizing transmitted neutrons while fully transmitting the laser light.
[0038] FIG. 3A is a schematic diagram illustrating a final beam transport system including two cascaded neutron pinholes according to an embodiment of the present invention.
Although the system can be referred to a "two neutron pinhole" system, it will be understood that the system utilizes two sets of neutron pinholes. Systems designed as illustrated in FIG.
3A experience a radiation dose that is attenuated to 0.04 rem/year utilizing two cascaded neutron pinholes. It should be noted that the final optic 326/320 not only focuses, but deflects the beam from the axis of the second neutron pinhole relay telescope (including focus lens 314 and Fresnel lens (type 2a) 316 and matching focus lens 315 /
Fresnel lens 318 to the target chamber center 386. Since the final optic (i.e., Fresnel lens (type 2b) 326 and matching final optic (i.e., Fresnel lens (type 1 b) 320 deflects the laser beam, it only acts as a scattering source for neutrons, thereby preventing ballistic neutrons from passing through the neutron pinhole at location. The transmitted spectrum of neutrons from the pinhole 330 will be a roughly collimated beam of neutrons that have scattered from the surrounding shield materials and blanket after some collimation by the pinhole structure. As shown in FIG. 3A, the axis of the second neutron pinhole at location 332 is again deflected from axis of the first neutron pinhole at location 330, which prevents ballistic neutrons from the second pinhole from passing through the first one. Using this technique, the neutron dosage can be attenuated to levels such that human occupation of the laser bay is possible.
[0039] In an embodiment, the laser bays 310A and 310B include 2.2 m wide x 1.35 m high x 10.4 m long lw lasers/amplifiers. These laser bays are able to produce laser beams with 435 mm square beam dimensions suitable for fusion applications. Additionally, in some embodiments, the inner cone 324 is characterized by an angle of 26.9 and the outer cone 322 is characterized by an angle of 47.25 , but these particular angles are not required by the present invention. As an example, in other embodiments, the cone angles are 30 and 50 .
[0040] The optical design of the final transport optical system meets many requirements simultaneously, including: the ability to point and center to incoming targets at the target chamber center, efficient transport of the 351 nm light to target chamber center, and focus of the energy into the Laser Entrance Hole (LEH) of the target hohlraum. To achieve these ends, the mirrors M10 and M1 1 shown in FIG. I are used to maintain centering on the final transport optics and slow pointing to the target. The lenses L9, L10, and L11 in addition to transporting the beam through the first neutron pinhole, also serve to null out the chromatic dispersion induced by the Fresnel final optic, which has the opposite sign relative to traditional convex lenses. The grating LG1 compensates for the temporal skew induced by the deflection (diffraction) of the Fresnel final optic and also serves to provide the deflection required between neutron pinhole 1 and 2. Thus fully compensated both chromatically and temporally, the Fresnel optic can focus the 351 nm drive laser beam into the LEH of the target.
[0041] Embodiments of the present invention utilize one of several optical elements as the final optic including: a grazing incidence metal mirror (GIMM), an elliptic mirror, a thin Fresnel optic, or the like. In embodiments utilizing a GIMM or parabolic mirror, an additional vacuum window is included in the design upstream (e.g., immediately) of the final optic before the neutron spatial filter. This optic serves two purposes among others: to guarantee vacuum at the telescope focus so that the laser light can be transmitted, and to serve as a tritium barrier. The Fresnel optic illustrated in FIG. 1 acts as both the final focusing optic and as the vacuum barrier. By making this final optic thin, the neutron induced absorption can be reduced to level of a few percent.
[0042] Although the angle between the optical axes of the two relay telescopes associated with the neutron pinholes is angled at an angle of about 60 , this is not required by the present invention and other embodiments utilized different angles between telescopes. In some embodiments, the first relay telescope is oriented in a horizontal plane and the second relay telescope is oriented in a vertical plane, with a right angle between the two optical axes.
Other orientations are included within the scope of the present invention in addition to those illustrated. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.
[0043] FIG. 3B is a schematic diagram illustrating a final beam transport system including a single neutron pinhole according to an embodiment of the present invention.
Referring to FIG. 3B, laser sources 350A through 350N are provided in a first region 351.
Light from the laser sources 350A through 350N is directed toward a shield wall 352, for example, a all 3 m in thickness. A set of neutron pinholes 353A through 353N are provided in the shield wall 352 to enable the laser radiation to pass through the shield wall after focusing using a set of optical system (e.g., a set of N relay telescopes). Thus, when this system is referred to as a "single neutron pinhole" system, this can be understood as utilizing a single set of neutron pinholes rather than two sets of neutron pinholes.
[0044] Light passing through the set of neutron pinholes 353A through 353N
reflects off parabolic mirrors 360 in the illustrated embodiment to impinge on Fresnel optics 362 and 364. In some embodiments, the distance between Fresnel optics 326 and 364 is sufficient to enable parabolic mirrors 360 to be positioned under ledge 361. After focusing by Fresnel optic 364, light is focused onto target 386.
[0045] Neutrons generated at the target 386 propagate out in all directions including cone 368, passing through the space between walls 366 and 365. Neutrons to the left of cone 368 are reflected or absorbed by wall 366. In an embodiment, wall 363 and ledge 361 define the angular spread of cone 368. Although the neutrons impinge on Fresnel optic 364, wall 365 prevents neutrons from impinging on Fresnel optic 362. Because the neutrons are contained between wall 363 and ledge 361, only a single set of neutron pinholes is needed to reduce the neutron density in region 351 to acceptable levels.
[0046] FIG. 3C is a simplified schematic diagram illustrating elements of neutron pinhole telescopes according to an embodiment of the present invention. As illustrated in FIG. 3C, a first telescope 370 focuses light through the secondary shield wall 372 to pass through a second neutron pinhole 374. The light is refracted through Fresnel optic 376A, which forms an element of a second relay telescope 370. The second relay telescope 380 focuses light through the primary shield wall (not shown) to pass through a first neutron pinhole at location 382A. As is evident by the figure, multiple, parallel light paths are provided by embodiments of the present invention, providing multiple neutron pinholes passing through the primary and secondary shield walls as illustrated by neutron pinhole 374B, light from which is collected by Fresnel optic 376B.
[0047] Light passing through the first neutron pinhole at location 382 is incident on Fresnel optic 384A, which collects and focuses the light onto the target 386. Because both grating structures present in Fresnel optics 376A and 384A receive light from a point source and focus light to a corresponding point source, the manufacturing of these Fresnel optics is simplified, enabling a high quality manufacturing process to be utilized. In order to manufacture these gratings, a point source is utilized to define the grating structures since light passing through the gratings originates and terminates as a point source. As illustrated, the gratings are receiving divergent light and producing convergence of the received light.
Thus, grating exposure can be accomplished using point sources. Various cone angles can be utilized according to embodiments of the present invention, for example, an angle of 26.9 for the inner cone between the target 386 and Fresnel optic 384A and an angle of 47.2 for the outer cone between the target 386 and Fresnel optic 384B.
[0048] According to some embodiments, the manufacturing process is improved in comparison to other architectures since point sources can be utilized in the grating definition process. As an example, Fresnel optics manufactured for use in embodiments as illustrated in FIG. 3C have reduced aberrations in comparison with Fresnel optics in which a divergent beam is collimated.
[0049] The inventors note that the neutron-induced absorption in fused silica saturates at fairly modest neutron irradiation levels, and this absorption can be partially annealed by raising the temperature of the substrate as illustrated in FIG. 4A. In an embodiment, a 5.3 mm thick fused silica substrate is utilized for the Fresnel optic, which is sufficient to serve as the vacuum barrier between the target chamber at 21 ton and the relay telescope at approximately 0.5 mtorr.
[0050] The inventors have determined that if an optic of sufficient thickness (e.g., a 5.3 mm thick optic) is maintained at ¨580 C, the absorption loss is reduced to ¨
0.5%. As illustrated in FIG. 4B, the absorption of fused silica optics varies as a function of temperature. The heating can be accomplished through use of beam heating, an external heater producing ¨3.4 MW, or a combination thereof. In embodiments in which no heater is used, the inventors have detennined that beam heating alone will raise the temperature of the optic to ¨518 C, with an associated transmission loss of 3.5%, which is suitable for some applications.
According to an embodiment of the present invention, a 5.3 mm thick fused silica Fresnel optic is utilized for the final optic, although embodiments of the present invention are not limited to this particular thickness. Other thicknesses can also be utilized.
[0051] FIG. 4A is a graph illustrating corrected transmission percentage as a function of wavelength for a final optic according to an embodiment of the present invention. FIG. 4B is a graph illustrating laser absorption versus temperature for a 5.3 mm thick fused silica optic.
[0052] Referring to FIG. 4A, the annealing processing of neutron damaged silica demonstrates a large change in 351 nm transmission as a result of the annealing process.
[0053] In addition to the neutron threat, a shock wave generated by the target ignition will be incident on the final optic. FIG. 5 is a simplified graph illustrating a shock pressure waveform incident on the final optic according to an embodiment of the present invention.
FIG. 6A is a contour plot illustrating induced stress in the final optic from the target ignition shock. FIG. 6B is a contour plot illustrating the maximum displacement of the final optic from target ignition shock. As illustrated in FIGS. 6A and 6B, there is about 2 um of displacement in the final optic and about 40,000 Pascals of stress, which is acceptable for the designs described herein.
100541 This optic can be mounted in a frame that can be sealed using a gasket seal to a transport telescope containing a neutron pinhole, which is a large cement structure connected to the building. In an embodiment, the aperture of the fused silica optic is approximately 0.53 x 43 x 49.65 cm3 (43cm aperture at angle of 30 ) with an external pressure of 21 ton (2800 Pa) and an internal pressure of 0.5 mtorr, which results in 134 pounds of force on the surface of the optic. An additional 0.5 ton (70 Pa) is incident on the final optic during the ¨135 jis shock pulse as shown in FIG. 5. To understand the mechanical effect of this impulse on the 5.3 mm thick optic, a model was built in quarter symmetry using a Shells model (a finite element gridding technique useful for thin substrates). For boundary conditions, the contact points to the gasket were modeled as knife edge rollers (supported normal to the optic only).
The first modal frequency is 131 Hz. The induced stress and displacement of the optic due to the impulse are shown in FIG. 6. The maximum effective surface stress is 40600 Pa. The maximum displacement is 2.62x10-6 m (2.62 m). Both the maximum displacement and maximum effective surface stress occur at approximately 6 ms into the analysis. These results indicate the final optic survival is not threatened by the shockwave, and the maximum surface displacement should not have a significant impact on the laser focal spot. It should be noted that mounting of the final optic can be designed to avoid resonance at the modal frequency or induced vibration from the building due to the previous shot and/or support equipment fluid flow (e.g., blankets, cooling, or the like). Engineering of passive damping mechanisms for the vibration can be performed based on the spectrum for this final optic including effects based on the chamber environment and the mechanical mounting hardware design.
[0055] As illustrated in FIG. 6A, the global maximum effective surface stress is 4.06 x 104 with a global minimum of zero. As illustrated in FIG. 6B, the global maximum displacement of the final optic is 2.62 x 10-6 m and the global minimum displacement is -2.47 x 10-6.
These values are not intended to limit embodiments of the present invention but to provide examples of the stress and displacement encountered in various embodiments of the present invention.
[0056] Embodiments of the present invention provide methods and systems for replacement of the final optic (as well as other optics between the two neutron pinholes) in a radiation hot environment. To first order, no electronics are able to survive in this environment and would have a low MTTF. The replacement hardware will have a very large MTTF, since failure of these components would require plant shut-down (affecting plant availability) to enable access to the hardware in the high radiation area around the target chamber.
[0057] FIG. 7A is a simplified schematic diagram of a final optic changeout system according to an embodiment of the present invention. The system illustrated in FIG. 7A
provides a dual optic replacement capability and simple mechanical replacement via a cable drive 720 into the high radiation area. FIG. 7B is a simplified schematic diagram of an optical pass-thru for final optic replacement including a labyrinth neutronics barrier in a shield wall according to an embodiment of the present invention. Some embodiments of the present invention are enabled by the geometry of the Fresnel optic, for example, 40 cm or 50 on a side, but only 5 mm thick and the associated low weight. The thin nature of the Fresnel optic 705 additionally enables removal through a thin labyrinth 730 as illustrated in FIG. 7B.
[0058] As illustrated in FIG. 7A, a system for replacement of the thin Fresnel optic 705 is provided that does not utilize any hydraulic or motorized devices in the high radiation area.
As illustrated in FIGS. 7A and 7B, this system and method uses cables with pulleys or rollers to guide damaged Fresnel lenses out of the high radiation environment through curved slits in the shield wall that serve as neutron labyrinths but allow exchange of the final optic. A close-up of one of these labyrinths is shown in FIG. 7B with dimensions that are used in an exemplary embodiment suitable for neutronics modeling.
[0059] Referring to FIG. 7B, optical assemblies pass through a labyrinth to prevent the neutrons from passing through the wall associated with the passage of the optical assemblies.
As illustrated in FIG. 1, the neutron pinholes provided for passage of the laser beams are oriented at an angle with respect to each other to prevent neutrons passing through the innermost pinhole as undeflected neutrons. The optical assemblies are able to pass through the labyrinth, which blocks neutrons as a function of the shape of the labyrinth. Referring to FIG. 7B, in some embodiments, the labyrinth has a width of 15 cm and a radius of curvature of ¨150 cm, providing a distance between entrance and exit ports of 300 cm for a 300 cm thick wall.
[0060] Although not illustrated in FIG. 7A for purposes of clarity, embodiments of the present invention utilize two cable systems (one for each Fresnel optic 705) with a cable attached at the top and bottom of each optic (i.e., 4 cables total running through the two labyrinthine slits in the wall). In other embodiments, other implementations can be utilized.
As illustrated in FIG. 7A, arrow 702A illustrates the movement of the left-hand optic during replacement and arrow 702B illustrates the movement of the right-hand optic during replacement.
[0061] Although the labyrinth illustrated in FIG. 7B is a continuous curved structure, this is not required by embodiments of the present invention. In other embodiments, a zig-zag labyrinth as shown in FIG. 7C is utilized.
[0062] Since, in some embodiments, there is no adjustment capability in the final optics, the mounting hardware enables precision kinematic replacement. This is achieved in the illustrated embodiment by creating a telescope end face 805 as shown in FIG.
8A, where ferromagnetic steel balls 825 (e.g., Nd-based magnets or other high strength to mass ratio magnets such as neodymium iron boron-based magnets, samarium cobalt-based magnets, or other similar magnets) are mounted into the surface to provide kinematic registration points 827 for the Fresnel optic module, also shown in FIG. 8A. In other embodiments, the kinematic mounts are reversed, with the magnets and kinematic registration points provided on the opposing elements (i.e., magnets mounted on the LRU and registration points on the telescope end face). As illustrated in FIG. 8A, the Nd-based high power magnets (which may be replaced with other suitable high strength to mass ratio magnets), the Fresnel optic, and vacuum gasket 830, are all mounted together on the final optic frame 807 that is a line replaceable unit. The precision frame can be fabricated from a rigid material such as stainless steel with cable attachments 840. To enable independent removal of window modules, two pairs of cable drives are provided as shown in the front view illustrated in FIG. 8B.
[0063] Referring to FIG. 8A, the end of the telescope includes a steel flange including kinematic nodules 825 on the end that are also made out of steel. The use of steel enables the elements illustrated in FIG. 8A to possess a lifetime similar to other chamber elements.
Elements that are replaceable are mounted to the steel flange, for example, the final optic 815 (e.g., the fused silica Fresnel lens, which can be mounted offline to provide micro-alignment capabilities), the gasket 830 for creating a vacuum seal at the surface, the Nd-based magnets 827, the attachments 830 for cabling, which is used to move the assembly into and out of the system during replacement and repair operations, and the like. In some embodiments, two assemblies are provided side-by-side and the left hand one would changed out to the left and the right hand one would get changed out to the right using two independent cabling systems.
As illustrated in FIG. 8B, independent cable pairs 852 and 854 enable allow window modules on both sides to be independently removable. In some implementations, the gasket is optional since some embodiments do not utilize a vacuum environment for portions of the system. In these embodiments, the optics can be mounted, but not sealed to a neutron pinhole, with no pressure differential present across the optic. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.
100641 FIG. 8C is a simplified flowchart illustrating a method of exchanging a final optic in a high radiation environment according to an embodiment of the present invention. The method 800 includes halting operations (810), optionally venting the telescope to chamber pressure (812), and optionally adding additional Xe gas to "burp" the lens from the telescope end face (814). The method also includes pulling the cable to retrieve the final optic through radiation wall (816), and exchanging the final optic using robotics in the region between neutron pinhole #1 and neutron pinhole #2 (818). The method further includes pulling the cable to position the replacement final optic in front of telescope end face (820), using the magnets to pulls the final optic into kinematic position (822), optionally pulling a vacuum to seat the final optic on kinematics (824), verifying the alignment and repointing the beam as necessary (826), and resuming operations (828). Although kinematics are utilized in the illustrated embodiment, this is not required by embodiments of the present invention and other alignment techniques are included within the scope of the present invention.
100651 It should be appreciated that the specific steps illustrated in FIG. 8C
provide a particular method of exchanging a final optic in a high radiation environment according to an embodiment of the present invention. Other sequences of steps may also be performed according to alternative embodiments. For example, alternative embodiments of the present invention may perform the steps outlined above in a different order. Moreover, the individual steps illustrated in FIG. 8C may include multiple sub-steps that may be performed in various sequences as appropriate to the individual step. Furthermore, additional steps may be added or removed depending on the particular applications. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.
100661 Although a particular method of sealing optics is provided in relation to FIG. 8C, embodiments of the present invention are not limited to these approaches. In other embodiments, a push-pull seal is utilized as a valve, similar to a canister's seal. Thus, embodiments of the present invention provide for seal creation at a distance by venting one side of a valve and then changing out the optic. By actuating a lever, a seal can be created as the optical mount is urged against a flange. In order to release the seal, the lever is actuated in an opposing direction to enable the optical mount to move away from the flange in a manner analogous to a canister lid. One of ordinary skill in the art would recognize many variations, modifications, and alternatives.
[0067] The method illustrated in FIG. 8C allows the passive method of magnetic kinematic mounting to maintain alignment across multiple servicing operations. All expendable components can be readily removed from the high radiation environment without shutting down the power plant for direct maintenance. All required pneumatic vacuum valves, motorized cable drive, and robotic optic exchange have been limited to the area between neutron pinhole #1 and #2. This area and access are schematically shown in FIG. 9A. An airlock door 920 which provides both vacuum and tritium barrier is located in an entrance of labyrinth 940, which keeps the laser bay radiation levels safe for personnel.
Robotic service vehicles 930 can enter supplying new materials (optics and/or hardware) to replace components. These same vehicles can be used to carry used components in shielded containers to radiation hazardous waste locations in the plant for recycling and/or disposal.
As illustrated in FIG. 9A, after the final optic is removed through the labyrinth into the lower radiation area 911, a vehicle is able to remove the optic through an interlock.
[0068] Embodiments of the present invention operate such that the pressure of this environment is low (-21 torr), which will prevent all but the lightest of particulates from remaining suspended in the chamber gas and thereby promote cleanliness. Gas purge nozzles can be located in the region of the final optic with their ultimate purpose being both to provide counter flow pressure to offset the "puffs" of chamber gas from target ignition and also to provide a low pressure "air knife" to clean the final optic as it is being replaced and maintain that cleanliness during operations. Control of this purge flow rate can be done using pneumatic valves located in low radiation areas outside of the primary shield wall. During maintenance operations this purge pressure can be briefly increased to enable gas cleaning of the final optic to meet requirements.
[0069] In addition to the systems to provide for long lived and replaceable final optics, embodiments of the present invention address concerns for the optics located between the neutron These optics (L11 and LG1 as illustrated in FIG. 9) and their associated hardware are in a radiation environment that compounds the threat to the optic and limits access and maintenance capabilities. Initial neutronics calculations show the neutron pinhole #2 (pinhole 925 in the primary shield wall 926) attenuating the 1.5 x 1017 n/m2 sec incident dosage significantly. These neutrons appear to be highly collimated, which will enable relatively simple neutron dumps to be used to limit the neutron flux in the area between the neutron pinholes. Motorized vehicles 930 and actuators with electronics will be allowed into this area for servicing and some components may be allowed permanent occupation in this area. Servicing of optics already in this area is much more straightforward and can be accomplished with handling methods commensurate with standard cleanliness protocols.
[0070] FIG. 9B is a simplified schematic diagram illustrating a laser bay labyrinth and neutron pinhole architecture according to an alternative embodiment of the present invention.
As illustrated in FIG. 9B, an architecture is provided that provides neutron shielding using a single set of neutron pinholes (e.g., the set of four neutron pinholes 950 shown in FIG. 9B).
[0071] Laser/amplifiers are provided in the laser bay 955, which is at atmospheric pressure and utilizes an air environment in the illustrated implementation. Light from the lasers/amplifiers is directed, using optics, to pass through the shield wall 952 including the single set of neutron pinholes 950. Utilizing other optics as illustrated, the laser beams, after passing through the set of neutron pinholes, are directed in a zig-zag manner around walls 956 and 958 to impinge on the target chamber 960. In the illustrated implementation, the target chamber 960 is at 21 torr, with a mixture of xenon and tritium, produced as a consequence of the fusion reactions. The labyrinth area 962 is at substantially the same atmospheric conditions as the target chamber, 21 ton with a mixture of Xe and T. Neutrons produced in the target chamber 960 that are propagating toward the labyrinth area 962 are blocked by walls 958 and 956 and are, therefore, not able to reach the neutron pinholes in substantial densities.
[0072] In order to replace optics, including the final optic 970, a cable/rail guided system 980 is provided to enable removal and replacement of optics as described more fully throughout the present specification. After their useful life, optics are removed using the cable/rail guide system 980 as they are routed along shield wall 982 and extracted through an airlock door 984, which also serves as a tritium barrier. After extraction through the airlock door 984, robotic optics replacement vehicles 990 can be used to remove spent optics and deliver new optics. The environment for the robotic optics replacement vehicles can be atmospheric pressure, for example, air.
[0073] Referring once again to FIG. 1, the final beam transport system provides a mechanism to direct the 351 nm laser light to the target chamber center. In contrast with some other fusion technology systems (e.g., NIF), the chamber is not at hard vacuum. In some embodiments, the chamber is intentionally filled with a protection mechanism, such as xenon gas at 4 g/cm3, to protect the chamber walls from ions and x-rays.
Target ignition at 15 Hz adds components of the target (hydrogen, deuterium, tritium, helium, carbon, lead, and the like) to this gas mixture as well since the vacuum system doe not typically replace all of the gas before the next shot. Therefore, a detailed analysis of the beam propagation through this complex gas mix has been performed to provide information related to the beam dynamics (e.g., filamentation or scattering due to nonlinear processes). The analysis begins by in one implementation by propagating the 2TW, 15 ns, laser beam at 0.351 tm through tens of cm of Xe/Pb plasma near target chamber center and meters of gas starting at the final optic. The generation and evolution of this target chamber environment is illustrated in FIG.
10.
[0074] Referring to FIG. 10, prior to the laser shot, the gas is at a non-ionized state with a 5% lead mixture at ¨ 0.5 eV. As the foot of the laser pulse begins to heat the target, a plasma ball farms that grows to an extent of 25 cm during the laser pulse. After ¨ 1 lis, the plasma has radiatively cooled to a hot mix of neutral gas, which continues to radiate until the next target shot.
[0075] The interactions of the laser with the gas and the expanding plasma are given in Table 2, where the interactions are characterized by type and an assessment of the effect on the beam is given. Most of the effects are well understood and will depend on the actual target gas mix and temperature environment. It should be noted that the primary loss mechanisms for the beam appears to be the ionized gas in the plasma ball surrounding the target. This transmission loss as a function of distance from the target is shown in FIG. 11A, and induces a negligible loss of 0.5% at 351 nm. In an extreme case in which the entire chamber were to remain ionized, the loss would only increase to 1.5% for the 61.tg/cm3 case.
The second loss mechanism of interest is Stimulated Raman Scattering from the lead gas from the target hohlraum. Electronic Stimulated Raman Scattering (scattering from bound electrons) has been extensively studied with dye laser in heat pipes (alkali vapors) in the past.
Conversion efficiency > 60 % was observed for Pb vapors around 1 ton. The inventors have determined that the intensity - length product for a LIFE beamlet is so large that the relevant gain exponent will reach 10X threshold (G ¨ 30) after the 1 ns of the laser impulsion. This will result in full saturation of the SRS medium.
[0076] Referring to FIG. 11B, lmJ of SRS @0.02 Ton corresponds to ¨ 1 photon per atom. Therefore, if all of the available lead atoms that are in the laser illumination volume in the target area are excited, this corresponds to ¨ 20 kJ for the entire LIFE
laser system (all beams), which would be equivalent to doubling the energy of the first "picket"
on the laser pulse shape. The SRS loss corresponds to a beamline loss of 0.83%. Based on these values, the apparent loss to the incoming beams is very reasonable ¨1.33 ¨
2.33% for all affects at the 6 p,g/cm3 case discussed herein. It should be noted that the previous analysis does not include the last centimeter of propagation (near the hohlraum LEH) where the beams begin to overlap, which is addressed by energetics analysis.
Interaction Assessment Laser- Inverse Bremstrahlung (photons less than 50 cm of beam path is ionized plasma absorbed by free electrons) and calculated I. B.
absorption is 0.5%
(free @ 6 [ig/cc Xe and 1.5 % @ 8 g/cm3 electrons) Xe Stimulated Brillouin scattering Gsbs <1 for a beamlet due to low (photons scattered by ion-acoustic density/low intensity waves) Stimulated Raman scattering (photon Gsrs < 1 for a beamlet due to low scattered by "free" electron plasma density/low intensity waves) Ponderomotive filamentation G << 1 (nonlinear plasma refraction) Laser- Raman scattering from bound not a problem for Xe/Xe; Pb debris gas/vapor electrons requires doubling the first picket energy (bound to saturate the medium (20 kJ) electrons) B-integral (index of refraction B-integral <0.1 radian for a beamlet; no nonlinear with intensity; Kerr effect) filamentation Refraction through a density gradient a 40 jig/cm3 cold Xe jet leads to a 301.im (beam deflection) / turbulence mispointing at 5m; turbulence likely not an issue Break down in Xe gas along the path breakdown threshold in Xe gas is to TCC reached ¨ 50 cm from TCC at peak power (11ns), while plasma ball radius is <25 cm, but density too low for cascading/self-focusing interaction with Xe droplets; Pb2 unlikely in 0.5 eV Xe/Pb gas dimers (Rayleigh scattering; break down; absorption) Table 2. Laser focal interactions with target gas [0077] It is also understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art and are to be included within the spirit and purview of this application and scope of the appended claims.
Claims (22)
1. A method of replacing an optical element positioned in a high radiation environment, the method comprising:
halting operations of a beamline;
pulling a cable to transfer the optical element through a radiation wall;
exchanging the optical element with a replacement optical element;
pulling the cable to transfer the replacement optical element through the radiation wall;
positioning the replacement optical element adjacent the first end face of the telescope;
seating the replacement optical element on the first end face of the telescope;
seating the replacement optical element on kinematic elements;
verifying an optical alignment of the replacement optical element; and resuming operations of the beamline.
halting operations of a beamline;
pulling a cable to transfer the optical element through a radiation wall;
exchanging the optical element with a replacement optical element;
pulling the cable to transfer the replacement optical element through the radiation wall;
positioning the replacement optical element adjacent the first end face of the telescope;
seating the replacement optical element on the first end face of the telescope;
seating the replacement optical element on kinematic elements;
verifying an optical alignment of the replacement optical element; and resuming operations of the beamline.
2. The method of claim 1 further comprising:
venting a telescope to chamber pressure; and adding a gas to separate the optical element from a first end face of the telescope, wherein seating the replacement optical element on the kinematic elements comprises pulling a vacuum to seat the replacement optical element.
venting a telescope to chamber pressure; and adding a gas to separate the optical element from a first end face of the telescope, wherein seating the replacement optical element on the kinematic elements comprises pulling a vacuum to seat the replacement optical element.
3. The method of claim 1 wherein the optical element comprises a lens.
4. The method of claim 3 wherein the lens comprises a Fresnel lens.
5. The method of claim 1 wherein the gas comprises Xe gas.
6. The method of claim 1 wherein the replacement optical element comprises a lens.
7. The method of claim 6 wherein the lens comprises a Fresnel lens.
8. The method of claim 1 wherein positioning the replacement optical element adjacent the first end face of the telescope comprises using kinematic magnets to position the replacement optical element.
9. The method of claim 8 wherein the kinematic magnets comprise at least one of Nd-based or Sm-based magnets.
10. The method of claim 1 wherein seating the replacement optical element on the first end face of the telescope comprises pulling a vacuum on the telescope.
11. An optical system comprising:
a vacuum chamber having a first end and a second end;
an optic mount mounted to the first end of the vacuum chamber, wherein the optic mount has a mounting surface;
a Fresnel optic mounted to the mounting surface;
a cable attached to the optic mount; and a second optical element mounted to the second end of the vacuum chamber.
a vacuum chamber having a first end and a second end;
an optic mount mounted to the first end of the vacuum chamber, wherein the optic mount has a mounting surface;
a Fresnel optic mounted to the mounting surface;
a cable attached to the optic mount; and a second optical element mounted to the second end of the vacuum chamber.
12. The optical system of claim 11 wherein the optic mount is positioned in a first region characterized by a first neutron flux and the second optical element is positioned in a second region characterized by a second neutron flux less than the first neutron flux.
13. The optical system of claim 12 wherein the first region is separated from the second region by a shield wall including a plurality of slits.
14. The optical system of claim 11 wherein the cable passes through a slit in a shield wall to a region characterized by a reduced neutron flux.
15. The optical system of claim 11 wherein the Fresnel optic comprises a fused silica optic.
16. A system comprising:
a laser system operable to provide a laser beam along an optical path;
a fusion chamber coupled to the optical path;
a neutron pinhole disposed along the optical path between the laser system and the fusion chamber; and a neutron attenuation region disposed along the optical path between the laser system and the fusion chamber.
a laser system operable to provide a laser beam along an optical path;
a fusion chamber coupled to the optical path;
a neutron pinhole disposed along the optical path between the laser system and the fusion chamber; and a neutron attenuation region disposed along the optical path between the laser system and the fusion chamber.
17. The system of claim 16 wherein the fusion system comprises a laser inertial fusion energy chamber.
18. The system of claim 16 wherein the laser system comprises a plurality of laser amplifier modules arrayed with respect to the fusion chamber.
19. The system of claim 16 wherein the system further comprises at least a mirror or a diffraction grating disposed along the optical path between the neutron pinhole and the fusion chamber.
20. The system of claim 16 wherein the neutron attenuation region comprises an additional neutron pinhole.
21. The system of claim 20 further comprising a turning mirror disposed along the optical path between neutron pinhole and the additional neutron pinhole.
22. The system of claim 16 wherein the neutron attenuation region comprises a labyrinth.
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| US61/437,177 | 2011-01-28 | ||
| PCT/US2012/022443 WO2012103150A2 (en) | 2011-01-28 | 2012-01-24 | Final beam transport system |
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| CA2824080A1 true CA2824080A1 (en) | 2012-08-02 |
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| JP (1) | JP2014511475A (en) |
| CN (1) | CN103339683A (en) |
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|---|---|---|---|---|
| CN103235393A (en) * | 2013-04-28 | 2013-08-07 | 哈尔滨工业大学 | Open-type high-flux big-caliber optical focusing and frequency conversion device |
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| US4518843A (en) * | 1982-09-01 | 1985-05-21 | Westinghouse Electric Corp. | Laser lens and light assembly |
| US4735762A (en) * | 1983-09-29 | 1988-04-05 | The United States Of America As Represented By The United States Department Of Energy | Laser or charged-particle-beam fusion reactor with direct electric generation by magnetic flux compression |
| US6428470B1 (en) * | 1995-09-15 | 2002-08-06 | Pinotage, Llc | Imaging system and components thereof |
| US7087914B2 (en) * | 2004-03-17 | 2006-08-08 | Cymer, Inc | High repetition rate laser produced plasma EUV light source |
| EP1852674B1 (en) * | 2006-05-05 | 2015-09-09 | Dr. Johannes Heidenhain GmbH | Measuring device for determining the relative displacement between two components |
| US9036765B2 (en) * | 2006-05-30 | 2015-05-19 | Advanced Fusion Systems Llc | Method and system for inertial confinement fusion reactions |
| US20110091004A1 (en) * | 2007-10-04 | 2011-04-21 | Lawrence Livermore National Security, Llc | Triso fuel for high burn-up nuclear engine |
| US7568479B2 (en) * | 2007-12-21 | 2009-08-04 | Mario Rabinowitz | Fresnel solar concentrator with internal-swivel and suspended swivel mirrors |
| US20090310731A1 (en) * | 2008-06-13 | 2009-12-17 | Burke Robert J | Single-pass, heavy ion fusion, systems and method |
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|---|---|---|---|---|
| CN103235393A (en) * | 2013-04-28 | 2013-08-07 | 哈尔滨工业大学 | Open-type high-flux big-caliber optical focusing and frequency conversion device |
Also Published As
| Publication number | Publication date |
|---|---|
| RU2013139868A (en) | 2015-03-10 |
| WO2012103150A2 (en) | 2012-08-02 |
| CN103339683A (en) | 2013-10-02 |
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| EP2668652A2 (en) | 2013-12-04 |
| JP2014511475A (en) | 2014-05-15 |
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