US2893624A - High vacuum - Google Patents

Description

G. FRICKE HIGH VACUUM July 7, 1959 3 Sheets-Sheet 1' Filed April 2, 1957 FIG.

July 7, 1959 G. FRICKE 2,893,624

HIGH VACUUM Filed April 2, 1957 3 Sheets-Sheet 2 y 7. 1959 G. FRICKE 2,893,624

HIGH VACUUM Filed April 2, 1957 3 Sheets-Sheet 3 v the area of further heating.

United States Patent HIGH VACUUM Gerhard Fricke, Heidelberg, Germany, assignor to Natlonal Research Corporation, Cambridge, Mass, a corporation of Massachusetts Application April 2, 1957, Serial No. 650,263

Claims priority, application Germany April 5, 1956 3 Claims. (Cl. 230-69) To produce an extremely high vacuum of less than mm. Hg a device is known in which the residual gas molecules are charged by the effect of thermal electrons so that the residual gas ions formed can be drawn from the high vacuum chamber by the influence of an electrically controlled field. It is further known how to vaporize in the very high vacuum chamber so-called getters (barium, titanium, or the like) which by deposition on the walls firmly bind a large part of the residual gas molecules.

The invention rests on a very effective ultra high vacuum pump in which ionized residual gas molecules continuously strike a moving support where they become fixd at the surface, which support can be provided with a corresponding absorptive coating (for example, metallic zirconium), and leave the ultra high vacuum chamber with the rotary motion of the support. In an adjoining space in which, for example, a normal high vacuum of about 10- mm. Hg is produced by an oil diffusion pump, the ionized residual gas molecules are removed by a local heating of the moving support. Tape or disc-like elements can be used as a support.

It is relatively diflicult to arrange a driving mechanism in the high vacuum and therein lies a further improvement of the invention in which a disc yields a simple and uniform driving device. As a support a disc of ferromagnetic material is used whose Curie point is relatively low. Especially suited is nickel or corresponding nickel alloys.

On this support is placed directly as a coating the absorptive medium for the residual gas ions. The ferromagnetic disc is also located in the nonhomogeneous field of a permanent magnet so that the magnetic field lines cross the disc preferably at right angles. By the local heating of the nickel disc in the higher pressure chamber, which is necessary to remove the absorbed residual gas molecules, the disc loses its ferromagnetic properties and becomes nonmagnetic. After the temperature has exceeded the Curie point (for nickel at about +275 0.), there exists in the field of the permanent magnet a substance asymmetrical with respect to the magnetic strength in which a corresponding torsion is exerted. Under this influence a rotation is started which brings the zone locally heated above the Curie point out of If the temperature drops only insignificantly below the Curie point, the original ferromagnetic properties are produced again immediately. It is thus possible to develop a continuous movement.

In some cases it is necessary to place the heated disc directly against cooled surfaces so that the locally developed heat drops quite rapidly. It is further possible to subdivide thermally the disc by radial inlays of material with poor heat conductance or to insert in simple fashion radial slits. In each case a further local heating should be assured. One should avoid heating the disc uniformly to a higher temperature since, after reaching the Curie point on all the surface of the sector within the 2,893,624 Patented July 7, 1959 magnetic field, a magnetically homogeneous relation exists which makes further rotation impossible.

The necessary local heating can, for example, be developed in a known fashion or by radiant heating or by eddy current heating or by electronic bombardment. To produce the residual gas ions an ionization device of known construction is used.

The driving of the support disc can further also occur in a known manner by a motor whereby the generated power is perhaps carried through a magnetic field into the high vacuum chamber.

In carrying out the invention moreover, the disc with the absorptive coating can be separated from the disc which secures the driving.

A further way of carrying out the invention uses as support for the ionized residual gas molecules a continuous belt which runs over a roll in the ultra high vacuum chamber and over a roll in the high vacuum chamber. The roll in the high vacuum chamber is joined over an axle through a high vacuum rotary duct of known construction with a driving motor. This causes the uniform driving of the support belt. Metal is preferably used as the material for the support belt. All remaining sepa rate parts of the arrangement correspond logically to the already described examples of practice.

Figs. 1 and 3 illustrate a first method of practice and Figs. 2 and 4 a second method for an apparatus for performing the process according to the invention.

In Fig. 1 in a chamber 1 in which the ultra high vacuum is to be produced, there is located a thermal cathode 2 which emits electrons which are accelerated through an accelerating voltage between cathode 2 and accelerating electrode 3 in the direction perpendicularly to the surface of the accelerating electrode. The accelerated electrons strike in their trajectory the residual gas molecules and thus form residual gas ions. These are held by the absorptive coating 4 (zirconium or the like) and leave, by rotation of the disc 5, the ultra high vacuum chamber 1 by the aperture 6. The size of the aperture between the high and the ultra high vacuum chambers is so measured that in practice, because of the strong choking effect at very low pressures, no back streaming occurs. The disc or plate 5 is fixed to an axle 7 which touches at its ends on point supports 8 of the holding device 9.

After the absorptive coat charged with residual gas ions has reached aperture 6, there occurs in a small zone heating by bombardment with thermal electrons and by heat radiation. For this purpose there is a filament 10 before which a slit 11 is arranged (see Fig. 3).

Under the influence of the magnetic field which, for example, is produced by a permanent magnet 12 with correspondingly formed poles 13, the area of the disc 5 demagnetized by heating, is moved in the direction of the gradients of the lines of the magnetic field. On heating, the fixed residual 'gas molecules are again released from the absorptive coating and are then removed in the usual manner from the high vacuum chamber 14, for example, by an oil diffusion pump 5. The oil diffusion pump works in combination with a fore pump 16.

The power supply of the emission cathodes comes from corresponding current sources 17 and 18 while the necessary accelerating voltage and the negative initial potential of the support are supplied by further current sources 19 and 37. All current supplies are introduced by known methods through vacuum-sealed ducts into the vacuum chambers.

In the mode of operation according to Fig. 2 a continuous belt 20 is used as the moving support. The guidance occurs over two rolls 21 and 22, of which the roll 22, placed on the side of the high vacuum, is coupled by a driving axle 23 through the high vacuum seal 24 with a driving motor 25 (for this see Fig. 4).

assassin Analogous to the mode of practice according to Fig. 1 the support 20, here in belt form, runs through a narrow opening 26 which completely prevents any back streaming between the high vacuum chamber 27 and the ultra high vacuum chamber 28. In the ultra high vacuum chamber 28 there is an ionization device 29 and 30 whereby the ionized residual gas molecules strike the surface of the support belt 20 and are afiixed thereon. The movement of the support 20 carries them from the high vacuum space 27 where they are again freed from the surface of the belt by heating.

The necessary heat can be produced by various methods already known. Radiant heating, eddy current heating, bombardment with thermal electrons, etc., are usable. In the present operating example a filament 31 was used. The residual gas molecules are removed from the high vacuum chamber 27 by an oil difiusion pump 32 which has a rotary oil-air pump 33 as a fore pump. The necessary operating current for the cathodes, accelerating electrode and support comes from current sources 34, 35, 36 and 38.

Through the present invention there is created an ultra high vacuum pump according to an entirely new working principle which makes it possible to attain extreme values of vacuum of almost 10-" mm. Hg at relatively high pumping speeds.

Since certain changes may be made in the above process and apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limting sense.

What is claimed is:

1. Apparatus for producing a high vacuum in a closed chamber which comprises in combination, a first vacuum tight chamber to be evacuated to a high vacuum, means for ionizing residual gas molecules in said first chamber, a second vacuum tight chamber, pumping means connected to said second chamber for evacuating said second chamber, an opening between said first and second chambers which is less than the free path of residual gas molecules, a disc of a ferromagnetic metal with a low Curie point Within said opening and rotatable between said chambers, said disc having an absorptive surface for residual gas ions, magnet means within said second chamber and positioned about a portion of said disc so that the magnetic field lines cross the disc substantially at right angles, and heating means spaced from said magnetic means for releasing gas from the absorptive surface and for locally demagnetizing said disc.

2. The apparatus of claim 1 wherein said disc comprises a metal selected from the group consisting of nickel and nickel alloys.

3. The apparatus of claim 1 wherein the absorption surface of said disc comprises zirconium.

Hickman June 6, 1939 Alpert Oct. 8, 1957

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