WO2008098913A1

WO2008098913A1 - An apparatus for activating a plasma focus unit

Info

Publication number: WO2008098913A1
Application number: PCT/EP2008/051645
Authority: WO
Inventors: Gianluigi Basile
Original assignee: O.C.E.M. S.P.A.
Priority date: 2007-02-14
Filing date: 2008-02-12
Publication date: 2008-08-21
Also published as: ITBO20070080A1

Abstract

An apparatus for activating a plasma focus unit, comprising a first electric mesh (E1), in turn comprising: the plasma focus unit (PF); a bank of capacitors (C) derived from a first tension node (A) and a second tension node (B); a switch (SW1), and a diode (D1) for conducting the current (ic) when the potential of the node (A) is greater than the potential of the node (B). The apparatus further comprises an additional electric branch (RA) connected to the bank of capacitors (C) to define an electric mesh (E2), comprising: a diode (D2) for conducting the current (ic) when the potential of the node (B) is greater than the potential of the node (A); and a current switch (SW2).

Description

AN APPARATUS FOR ACTIVATING A PLASMA FOCUS UNIT

TECHNICAL FIELD

The invention relates to the technical sector of apparatus for supplying a plasma focus unit and activation thereof.

BACKGROUND ART

As is known, a Plasma Focus unit is a device that enables generation of nuclear fusion reactions: it comprises two coaxial cylindrical electrodes, facing one another, the dielectric of which is constituted by a gas or gas mixtures, for example deuterium or a mixture of deuterium and tritium, maintained at a controlled pressure. The fusion reaction takes place following generation of an electrical discharge of a given intensity through the dielectric, caused by a determined tension difference applied across the electrodes; by way of example, a plasma focus unit can be designed such that a current spike of the order of a million amperes corresponds to an application of a difference of 30 kVolts across of its electrodes, such as to generate a nuclear fusion reaction.

Figure 1 shows a circuit for supplying a plasma focus unit of known type.

The circuit includes an electrical mesh Ei in which the following are inserted: the plasma focus unit PF, a capacitor bank C, and a first switch, for example of the spark gap type SWi, known to the expert in the sector, of dimensions which will support conduction of high current spikes. The bank of capacitors C, derived between a first A and a second node B, is energised by an external supply source ES, which is destined to charge the capacitors C of the bank to a predetermined tension level (potential difference between the nodes A, B) when the first switch SWi is open.

Once the bank of capacitors C is charged at a predetermined tension V₀, then the first switch SWi is closed; tension V₀, now present across terminals H, K of the PF unit, is such as to determine a violent discharge of current i_c through the dielectric, with consequent generation of a nuclear fusion reaction. The application of the tension difference V₀, as is known, generates circulation of an oscillating current io, damped over time, at a frequency which is the same as the resonance frequency for the first mesh Ei; in this case, the resonance frequency depends on the inductance value L_p of the first mesh Ei (typically constituted by only the parasitic inductances) and the equivalent capacity of the capacitor bank C, while the damped effect on the amplitude of the oscillating current, which lasts only a few hundredths of a nano-second, is due mainly to the resistive behaviour of the PF unit.

It has been experimentally proven that the nuclear fusion reaction occurs, in a single occasion, during the first half-period of the circulating current in the first mesh Ei. It follows that protraction of the electrical charge internally of the dielectric of the PF unit, and thus the circulation of current i_c in the first mesh Ei after the fusion reaction, constitutes a useless dissipation of energy which leads to complete discharging of the capacitor bank C. The successive fusion reaction, therefore, is subordinated to a complete charging of the capacitor bank C from tension zero to tension V₀, which requires a considerable amount of time (for charging) and energy.

In the light of the above drawbacks in the prior art, the aim of the present invention is to provide an apparatus for activating a new- concept plasma focus unit which offers greater energy saving in repetitive use with respect to prior-art devices, given a same number of nuclear fusion reactions obtained over a time unit.

In addition, a further aim of the invention is to provide an apparatus for activating a plasma focus unit, which apparatus has higher productivity than those in the prior art, in order to increase the number of nuclear reactions achieved in a given time unit.

A still further aim of the invention consists in providing a reliable and functional apparatus having relatively contained costs with respect to the advantages attained.

DISCLOSURE OF THE INVENTION

The above aims are obtained by means of an apparatus for activating a plasma focus unit, of a type comprising at least a first electric mesh, in turn comprising: the plasma focus unit; a bank of capacitors derived from a first tension node and a second tension node, with the bank of capacitors being destined to be charged by a supply device to a predetermined potential difference, greater in the first node than in the second node; and a first switch, characterised in that it comprises a first component, inserted in the first electric mesh, for unidirectional conduction of the current generated by the bank of capacitors when the potential of the first node is greater than the potential of the second node, and in that it further comprises an additional electric branch derived between the first node and the second node, to define a second electric mesh, in which, apart from the bank of capacitors, a second component for unidirectional conduction of the current generated by the -A-

bank of capacitors when the potential of the second node is greater than the potential of the first node.

BRIEF DESCRIPTION OF THE DRAWINGS

The characteristics of the invention which do not emerge from the above will be more fully detailed in the following, in agreement with what is written in the claims and with the aid of the accompanying figures of the drawings, in which:

figure 1 is an electrical diagram of an apparatus of known type for supplying and activating a plasma focus unit;

figure 2 is the electrical diagram of the apparatus of the present invention for supplying and activating a plasma focus unit;

figure 3 contains two graphs representing the progression over time of two significant electrical quantities;

figure 4 includes the electrical diagram of several apparatus of the invention for supplying and activating a plasma focus unit.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference to figure 2, the apparatus of the present invention comprises a circuit for supplying and activating the plasma focus PF unit, made up of a first mesh Ei and a second mesh E₂ and energised by an external supply device ES via the first node A and the second node B.

As in the prior art solution described herein above, and represented in figure 1 , the first electric mesh Ei comprises a parasitic inductance L_p, the bank of capacitors C, derived between the nodes A, B, the plasma focus unit PF and the first switch SWi, for example a spark gap or a solid state switch; in addition, the first mesh Ei includes a first unidirectional component Di, such as a specially shaped diode, for unidirectional conduction of the current when the potential difference V_AB between the first A node and the second B node is positive (the potential of the first node A being greater than that of the second node B). By way of example, in place of the diode the above-cited unidirectional component Di can be integrated directly into the switch SWi, which can be, for example, a Silicon Controlled Rectifier.

The second electrical mesh E₂ includes the bank of capacitors C and an additional branch RA derived across the bank of capacitors C; it comprises, apart from the bank of capacitors C, an additional inductor L_A of a specific value, for example higher than that of the inductance L_p of the first mesh Ei (for reasons which will be more fully explained in the following), a second switch SW₂, for example of the spark gap or solid state type, and a second unidirectional component D₂, for example a specially-sized diode for unidirectional conduction of the current when the potential difference V_AB between the first node A and the second node B is negative.

There follows a description of the operation of the apparatus of the present invention, with reference to the graphs of figure 3, which relate to the progression of the tension V_AB across the bank of capacitors C and the current i_c circulating there, which alternatively flows in the first Ei(to≤t≤ti) and the second mesh E₂ (t₂≤t≤t₃).

Starting from a condition in which the bank of capacitors C is uncharged, i.e. in which the tension V_AB at its terminals is nil, and in which the first switch SWi and the second switch SW₂ are open, the external device ES is activated to supply the bank of capacitors C with a suitable charge current (not indicated) up until a determined potential difference V₀ is reached at the terminals (condition V_AB=V₀ at time t≤t₀), conventionally considered positive (potential in the first node A is greater than that at the second node B).

At time to the first switch SWi is closed and this causes (without considering, for the sake of simplicity, delay times) circulation of a current i_c, generated by the bank of capacitors C, which can flows only in the first electric mesh Ei; the tension at terminals H, K of unit PF is such as to cause a discharge through the dielectric, closing the circuit in the first mesh Ei. As is known, the current i_c generated exhibits a damped oscillation, having a frequency which is equal to the resonance frequency for the first mesh Ei, (having regard to the equivalent capacity of the bank of capacitors C and the relative parasitic inductance L_p); however, the presence of the first diode Di enables circulation of the current i_c only in the relative first half-period (figure 3, to≤t≤ti), in which however there occurs a fusion reaction internally of the plasma focus PF unit (time t^*, indicatively denoted in figure 3); at the end of the first half-period (time ti), the current i_c is annulled and the tension V_AB in phase quadrature with respect to the current i_c is negative and modularly less than the tension V₀ (V_AB=-V_I , V_I<V₀), by effect of the dissipation of energy into heat (the Joule effect) on the resistances of the first mesh Ei (parasitic resistance and equivalent resistance of the PF unit, neither shown in the figure).

At this point, when the current i_c in the first mesh Ei is exhausted, as mentioned due to the effect of the first diode Di, the first switch SWi opens; the potential difference across the bank of capacitors C is now negative and equal to Vi (potential of the second node B greater than that of first node A).

At generic time t₂>ti, the closing of the second switch SW₂ is commanded, causing circulation of a current i_c generated by the residual energy stored in the bank of capacitors C and now directed oppositely on this branch, which can be directed only in the second electric mesh E₂; in this case too the current exhibits a damped oscillation over time, having a frequency which is the same as the resonance frequency for the second electric mesh E₂, where the resonance frequency depends on the value of the additional inductance L_A and the equivalent capacity of the bank of capacitors C, and the damped effect on the amplitude can be imputed to the parasitic resistance (not represented) of the second mesh E₂. The current i_c which runs in the second mesh E₂ is exhausted at the end of the relative half-period (time t₃), as it cannot invert due to the presence of the second diode D₂; the tension V_AB across the bank of capacitors C, in phase quadrature with respect to the current i_c, over time t₂-t₃ inverts its polarity, reaching a value V₃ which is lower than Vi, by effect of the dissipation of energy in heat (Joule effect) on the parasitic resistance of the second mesh E₂.

The difference of potential VAB across the bank of capacitors C, equal to V₃ is therefore newly positive even though it is lower than the tension V₀ required for a new impulse. The current i_c which runs in the second mesh E₂ exhibits an amplitude and a frequency which are lower than those circulating in the first mesh Ei, as the additional inductance L_A is greater than the parasitic inductance L_P (L_A>L_P); this is advantageous in terms of both the losses due to the Joule effect, which are lower than those on the first mesh Ei, and for the dimensions of the second switch SW₂, which can be less expensive than the first switch SWi. The following state, not illustrated in figure 3, in which both switches SWi, SW₂ are open, includes activation of the external device ES for supplying the bank of capacitors C up to complete resetting of the tension V₀. The successive operating cycles are repeated similarly: at the end of each cycle, only the energy required for charging the bank of capacitors C from tension V₃ to tension V₀ will need to be supplied, necessary for obtaining the nuclear fusion reaction internally of the plasma focus unit.

After the first start-up cycle of the apparatus of the invention, the subsequent nuclear fusion reactions advantageously each require a quantity of electrical energy which is much lower than the amount required in the prior art: in known apparatus, at each cycle the resonance current circulating in the first mesh Ei is extinguished, with a consequent total discharge of the bank of capacitors C and the energy stored there; with the present invention, the current i_c circulates in the first mesh Ei for only a half-period, sufficient for the nuclear reaction, and further circulates in the second mesh E₂ for a further half-period, in order to enable the inversion of the polarity of the residual tension

(V_AB=-V_I) across the bank of capacitors C, but with a much lower intensity. As a result, the bank of capacitors C supplies only a relatively contained part of the energy previously stored during the charging stage

(in which, as mentioned, it reaches a potential difference Of V₀).

By direct consequence, the external supply device ES will need much less time to restore the energy passed by the bank of capacitors C during each operating cycle, given that now it only has to supply a part of the total demanded; this advantageously enables a considerable increase in the productivity of the apparatus of the invention, as each cycle time depends greatly on the time required for charging the bank of capacitors C to the desired tension V₀. It is clear that charging starting from a tension V₃ of the order of V₀ will require much less time with respect to what occurred in the prior art, in which charging started from zero tension.

In other words, considering the same productivity required for other known-type solutions, the apparatus of the invention enables installation of an external supply device ES of a much lower power, with a consequent considerable reduction in the relative costs and sizes thereof.

A still further advantage of the present invention is that it provides an apparatus for activating a plasma focus unit which is reliable, functional and has relatively contained costs with respect to the advantages it offers.

Note that in some applications the discharge current required for generation of the nuclear fusion reaction of the plasma focus unit can reach extremely high values, with current spikes up to the order of a million amperes; in these cases correct dimensioning of the bank of capacitors C, the diode Di and the switch SWi in the mesh Ei (figure 2) can become problematic and expensive, so it is advisable, even when not necessary, to have several apparatuses of the invention derived from the same plasma focus unit; this solution has been illustrated in figure 4. Thus a plurality of electrical meshes MEi, ME₂, ...., ME_N are provided, each of which is destined to contribute via the relative bank of capacitors Ci, C₂, , C_N to the definition of a current i_Ci, ic2, ■ ■■■, icN representing the quota part of the discharge current i_c required for generating the nuclear fusion reaction of the plasma focus unit; in figure 4 each additional branch and supply device (of the type illustrated in figure 2) derived from the terminals J, K (with J=1 , 2, ..., N) of the corresponding bank of capacitors Ci, C₂, , C_N has been represented, for the sake of simplicity, by a relative additional block BAi₁ BA₂, ...., BA_N.

In this way a circuital configuration with a single supply mesh Ei, shown in figure 2 and for which configuration it might be problematic and expensive to size the diode Di and the switch SWi, can be substituted by the circuital configuration illustrated in figure 4, which shows a plurality of supply meshes MEi, ME₂, ... ME_N each provided with a relative diode and current switch dimensioned only for the current of branch i_Ci , ic2, ■ ■ ■ -,

Alternatively, a first variant (not illustrated in the figures) includes omission of the additional inductor L_A; in this case, the circulating resonant current i_c, in the operating configurations, exhibits in the second mesh E₂ a frequency and amplitude value which is greater and which depends on the parasitic inductance (not indicated) of the second electrical mesh E₂ (which was before of insignificant entity in the presence of the additional inductor L_A); with respect to the above- described embodiment, the increase in current i_c in the second mesh E₂ will lead to greater dissipation of energy in heat, provided by the bank of capacitors C, further requiring the interposing of a second switch SW₂ having adequate characteristics for supporting higher current loads. The new tension value across the banks of capacitors C, starting from which the relative charge by the external device ES will have to take place, is thus lower than that (V₃) which would be obtained in the presence of the additional inductor L_A, in agreement with the preferred embodiment. The advantageous technical-functional characteristics of the present invention are still valid, however.

Additionally, a second further variant of the invention (also not shown in the figures) includes the omission of the second switch SW₂ in the additional branch RA and, possibly, of the additional inductor L_A (in agreement with the above-cited first variant); in this case, following the closure of the first switch SWi and the generation of a resonance current in the first mesh Ei, a resonance current originates in the second mesh E₂ (of the same type as the one described above when the second switch SW₂ is closed at time t₂) when the tension V_AB across the bank of capacitors C inverts and the potential at node B exceeds, by a predetermined amount, the potential of node A. For a certain time interval, two resonating currents circulate, which respectively flow in the first electric mesh Ei and the second electric mesh E₂, without prejudicing the nuclear fusion reaction internally of the plasma focus PF unit. Thus the advantageous technical-functional characteristics of the present invention are safeguarded.

The foregoing is provided by way of non-limiting example, so that any variants of a practical-applicational nature are considered to enter within the protective ambit of the invention as it is described herein above and as it is now claimed.

Claims

1 ). An apparatus for activating a plasma focus unit, of a type comprising at least a first electric mesh (Ei ), in turn comprising: the plasma focus unit (PF); a bank of capacitors (C) derived from a first tension node (A) and a second tension node (B), with the bank of capacitors (C) being destined to be charged by a supply device (ES) to a predetermined potential difference (V_AB), greater in the first node (A) than in the second node (B); and a first switch (SWi), characterised in that it comprises a first component (Di), inserted in the first electric mesh (Ei), for unidirectional conduction of the current (i_c) generated by the bank of capacitors (C) when the potential of the first node (A) is greater than the potential of the second node (B), and in that it further comprises an additional electric branch (RA) derived from the first node and the second node (B), to define a second electric mesh (E₂), in which, apart from the bank of capacitors (C), a second component (D₂) is included for unidirectional conduction of the current (i_c) generated by the bank of capacitors (C) when the potential of the second node (B) is greater than the potential of the first node (A).

2). The apparatus of claim 1 , characterised in that the additional electric branch (RA) further comprises a second switch (SW₂).

3). The apparatus of claim 1 , characterised in that it further comprises an additional inductor (L_A) inserted in the additional branch (RA).

4). The apparatus of claim 1 , characterised in that it further comprises an additional inductor (L_A) inserted in the additional branch (RA), the value of which inductance is greater than an equivalent parasitic inductance (L_p) of the first electric mesh (Ei). 5). The apparatus of claim 1 , characterised in that the first switch (SWi) is of a spark gap type.

6). The apparatus of claim 1 , characterised in that the first switch (SWi) is of a solid state type.

7). The apparatus of claim 1 , characterised in that the second switch (SW₂) is of a spark gap type.

8). The apparatus of claim 1 , characterised in that the second switch (SW₂) is of a solid state type.