US2857542A - Anode structure for gas tubes - Google Patents

Description

Oct. 21,l 1958 2,857,542

c. E. cuRTls ANoUT STRUCTURE FoR GAS TUBES L Filed July l, 1955 United States Patent O signments, to the United States of'America as represented by the Secretary of the Army Application July 1, 1953, Serial No. 365,419

8 Claims. (Cl. 313-199) This invention relates to gas discharge devices and particularly to an improved anode structure for gas discharge devices.

During the operation of gas discharge devices, or tubes, the anode is, at certain times, at a potential that is negative with respect to the cathode. An example of this occurs during the inverse portion of the cycle when the anode is at a potential that is negative, with respect to the cathode. When the anode is negative in potential, with respect to the plasma inthe tube, positive ions are driven into the anode. The positive ion bombardment produces certain undesirable results in gas discharge devices.

One of the disadvantages caused by positive ion bombardment of the anode is that the tube life is shortened. This occurs due to the fact that the positive ions are physically driven into the anode material and permanently withdrawn from the tube atmosphere resulting in gas cleanup and thus a shortened tube life.

Another problem that is caused by positive ion bombardment of the anode is that in some gas discharge devices sputtering of anode material may be so great as to coat the walls of the envelope with metal from the anode. When this occurs, insulation of the various electrodes one from the other, is extremely diicult if not impossible.

A further problem involved in the development of gas discharge devices is reduction of the tiring time. For certain uses it is desirable to have a gas discharge tube with a very fast ring time, in other words a gas tube wherein the ring of the tube occurs practically instantaneously after the proper potentials have been applied to the various electrodes. In order to decrease the tiring time of gas tubes itis necessary tohave quick and efficient ionization of the enclosed medium. One method of increasing the eliciency of the ionization process is to increase the spacings between the cathode and anode so that a greater number of ionizing collisions will occur as an electron is propelled through the space. However, at certain times it is undesirable to increase the electrode spacings because of long path discharges, in accordance with Paschens law, on the inverse portion of the cycle. Thus, prior to this invention, a balance of the factors of eticient ionization and The plasma particles that have diffused out must be replaced, .resulting in the arc drop.

'It is therefore an object of this invention to provide a new and improved gas discharge device.

It is another object of this invention to provide a novel f ygas discharge device having a longer tube life.

Patented Oct. 21, 1958 "ice It is a further object of this invention to provide a new and novel gas discharge device having a faster `tiring time. It is a still further object of this invention to provide a new and novel gas discharge device wherein the arc drop is decreased. l

These and other objects have been accomplished in accordance with the general aspects of this invention by providing a gas discharge device including a cathode, a control electrode, and a hollow apertured anode. The aper-l tures in the anode are arranged adjacent the apertures in the grid and are in substantial alignment therewith. The hollow portion, or depth, of the anode is large enough in size so that substantial amount of ionization occurs within the `anode structure.

The novel features which are believed to be characteristic of this invention are pointed out with particularity in the appended claims. 'Ihe invention itself however will best be understood by reference to the following description when read in connection with the accompanying single sheet of drawings in which:

Figure l is a sectional view of a gas discharge device constructed in accordance with this invention;

Figure 2 is a transverse sectional view of the device shown in Figure 1 taken along line 2 2 of Figure 1; and Figure 3 is a sectional view of a modification of a gas discharge device constructed in accordance with this invention. A

Referring now to Figure l in greater detail there is shown a sectional view of a gas discharge device 10 constructed in accordance with this invention. The device 10 comprises a 'sealed envelope 11 having a conventional stem 12 through which lead-in `conductors 13 are sealed in the usual manner. -Enclosed within the envelope 11 is an ionizable medium which may be any of the well known gases or vapors at a pressure suicient to sustain an ionizing discharge within the envelope 11. The electrode structure is supported within the envelope 11 by means of the transverse insulating members 15 and 16 which are in turn supported by support rods 17 in the conventional manner as shown. The electrodes included within the envelope are a concentric arrangement of an indirectly heated thermionic cathode 20, a control electrode 24, and an anode 30. The cathode 20 may be any of the conventional types of cathodes and is preferably a thermionic cathode having an electron emissive coating thereon. The cathode 20 is heated by heater element 21 and is energized by an electrode as shown.

Spaced concentrically around cathode 20 is a control electrode 24 comprising a plurality of spaced apart horizont'al strips 24 and a plurality of spaced apart vertical strips 24", arranged in contact with each other to forma plurality of spaced apart apertures 25. lt should be understood that otherwell known structures may be used for the control electrode such as wire mesh. The size of the apertures 25 may vary over a considerable range`depending upon the desired use for the device 10. An example of the range of the size of apertures 25 is that the aperture may be as small as l mil and as large as l inch. This range of aperture size is given merely as an example and is not intended to thereby limit the invention.

Concentrically spaced around the control electrode 24 `is a hollow anode 30 having an apertured portion 31 tures 32 in the anode is also dependent upon the desired 1 use of the device 10, and should be as large, or larger than, the apertures 25 in the control electrode 24. It should be understood that other well known structures may be utilized forthe apertured portion 31 such as a wire mesh, or a stamped metallic plate. l a

The'depth of the hollow portionA of the anode30, i.e. the space existing between the apertured portion 31 and the outermost portion of the anode 30, is dependent upon the gas pressure and the type of gas that is used in envelope 11.V This spacing should be several times the mean free path `of the positive ions of the gas.

yThus the anode 30 encloses a field free space with which apertures 32 communicate and are in substantial alignment ,with the apertures 25 of control electrode 24.

The spacing between the control electrode 24 and the.

apertured portion of the anode 30 is determined by the proposed use for the device 10. This spacing is preferably close, i. e. in the order of a mean free path of an electron of the enclosed medium, but the invention is'notintended to be limited to such close spacing.

A specic example of a device constructed in accordance with this invention, given merely as an example and not intended to limit the invention, is as follows: The gas discharge device 10 may have a lling of xenon at a pressure of approximately 70 microns thus having a mean free path of the positive ions of .O cm. The grid to anode spacing could be less than the mean free path of the positive ions, while the depth of the hollow anode 30 would be approximately .5 cm., in other words several times the mean free path.

In operation, when a potential difference is applied between the cathode 20 and the anode 30, with a suciently positive voltage on the control electrode 25, current is conducted through the device 10. Because of the apertures 32 in the anode 30, electrons lfrom cathode 20 -pass'through the apertures 32 and thus travel a long path even though the spacing between the grid 25 and anode 30 may be small. Because of this long path the electrons have more ionizing collisions resulting in a plasma being formed very quickly so that the device has an extremely fast tiring time.

During the conductive portion of the cycle the arc drop of device 10 is decreased due to the structure shown. The reason for this is that a surplus plasma is formed inside the anode 30 that diffuses out through apertures 32 to replace some of the plasma particles that are lost to the electrode supports, insulating material etc. Be-

causeV the arc drop is decreased the device is very ecient. During the inverse portion ofthe cycle the surplus plasma remaining in the anode 30 will tend to diffuse to the walls of the anode. However, if the operating frequency is high, some of the surplus plasma will remain inside of the anode during the entire negative portion of the cycle.

During, the inverse portion of the cycle, i. e. when anode 30 is negative with respect to cathode 20, positive ions in the cathode to control electrode region are swept through the apertures 25 of the control electrode 24, and on through the apertures 32 of the anode 30 where the positive ions lose their energy by collisions with gas atoms in the field free space inside of the anode 30. Since the positive ions collide with gas atoms inside the anode 30, instead of being driven into the anode material, gas clean up is substantially eliminated by the structure of device 10. v Referring now to Figure 3 there is s-hown a modification of a gas discharge device constructed inaccordance with this invention. The device comprisesa sealed envelope 33 enclosing an ionizable medium. Within the envelope-there is supported a pair of transverse insulating members 34 and 35 which are supported by means of. support rods 36. Arranged between the insulating ,members 34 and 35 are a pair of cathode discs 37 and 38 respectively. Supported between'the cathode discs 3 7.vand 38 is an indirectly heated cathode 39v surrounded by a filament 40.

Supported above insulating spacer 34 is an apertured control electrode 41 having apertures 42 therein. ported above the apertured control electrode 41 is an insulating spacer 43 which supports a hollow apertured anode 44 having apertures 45 therein that are preferably aligned with the apertures Y42` of the control electrode 41.`

The anode 44may be held in position by means of transverse insulating member 46 as shown.

The depth of the hollow anode 44 is in this arrangement, as it was in Figure l, several times greater than rality of apertures therethrough,v said anode comprising i a hollow structure enclosing a space and having a plurality of apertures through the surface thereof adjacent to said apertures in said control electrode, said apertures insaid anode being in alignment with said apertures in said control electrode, and the depthof the space ven'-` closed by said anode being greater than the length of the mean free p ath of a positive ion of said gas.

2. A gas discharge device comprising a sealed envelope having an ionizable gaseous mediumtherein, a cathode, a control electrode coaxially spacedaround said cathode,

said control electrode having a plurality of apertures a therethrough, an anode completely enclosing a substan` tially -teld free space therewithin coaxially spaced around said control electrode, the depth of the space Aenclosed by said anode being greater thanthe mean free path of.

an ion in said medium, a plurality of apertures in the surface of said anode adjacent to said control electrode and each opening into said ield free space, and said aper tures in said anode being in alignment with said-apertures inV said control electrode.

3. A gas discharge Vdevice as in claim 2 whereink `the apertures in said anode Vare larger than the apertures in;

said control electrode.

4. A gasdischarge device comprising` a sealed envelope having an ionizable gaseous medium therein, an

elongated cathode within said envelope, a control electrode coaxially spaced around said cathode, said control electrode. including a plurality of apertures, a hollow anode coaXially spaced around said control electrode, said anode including an apertured portion adjacent to saidcontrol electrode and a solid tubular portion spaced around saidv apertured portion, said anode further in-` cluding a pair of transverse end plateseach connecting said'apertured portion tosaid solid portion whereby said anodecompletely encloses a space, said solid portion ofV said anode being spaced from said' apertured portion: a distance that is several times the mean free pathof the positive ions ofsaid medium, and said apertures insaid apertured portion of said anode being in alignment with said apertures in said control electrode.

5. A gas discharge device as inclaim 4 wherein the apertures in said apertured portion of jsaid anode are larger than the apertures in said control electrode.

6. A gas discharge device comprisinga sealed envelope having an ionizable gaseous medium therein; a cathode, a control electrode and a hollow anode spaced in that order in said envelope, said control electrode including a plurality of apertures, said anodeincluding an apertured portion adjacent to said control electrode and a solid portion lspaced from said apertured portion, said anode further; including means joining. the, peripheryy of said solid portion and said apertured portion .to form a Supn rfi. www( 8. A gas discharge device as in claim 6 wherein said apertures in said apertured portion of said anode are substantially the same size as said apertures in said control electrode.

References Cited in the file of this patent UNITED STATES PATENTS Steenbeek Jan. 7, 1941 Lamm Aug. 10, 1948

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