US2812465A - Gaseous-discharge device - Google Patents

Description

Nov. 5, 1957 K. J. GERMESHAUSEN 2,812,465

GASEOUSDISCHARGE DEVICE Filed may 10, 1954 2 Sheets-Sheet 1 w I l- Y www Arrows Nov. 5, 1957 K. J. GERMESHAUSEN 2,812,465

GASEOUS-DISCHARGE DEVICE Filed May 10, 1954 2 Sheets-Sheet 2 IAYIIII III I ATTORNEYS United States Patent C) GASEQUS-DISCHARGE DEVICE Kenneth J. Gerrneshausen, Newton Centre, Mass. Application May 10, 1954, Serial No. 428,446

8 Claims. (Cl. 313-207) The present invention relates to electric-discharge devices and more particularly to gas-filled devices in which an electric discharge takes places between an anode and a cathode disposed within the device.

An important application of gaseous-discharge tubes is that of producing flash illumination for such purposes as photography or stroboscopic observation or recording. Flash-tubes of this character embody an anode and a cathode disposed within the gas in the tube. When an electric discharge is produced within the tube between the anode and the cathode, a flash of light is emitted through the walls of the tube in the region between the anode and the cathode. During this flashing operation, however, some of the material of the cathode becomes sputtered off the cathode. At the time of the discharge between the anode and the cathode, due to the sudden release of energy in the gas and consequent heating, a momentary high pressure is built up between the anode and cathode that violently forces the gas normally disposed in the region of the tube between the anode and the cathode toward the ends of the tube beyond the anode and the cathode. This forced gas has been found to carry with it into the cathode end of the tube appreciable quantities of the material sputtered from the cathode. After the discharge flash, the gas driven into the cathode end of the tube returns to the space between the anode and the cathode, carrying with it substantial quantities of the sputtered material. This material is thereupon deposited upon the walls of the tube between the anode and the cathode, darkening the walls and reducing the amount of illumination that can pass through the walls of the tube. It is this factor of the darkening of the walls of the tube, and not the deterioration of the electrodes, that has been found to limit the effective life of many tubes of this character.

An object of the present invention is to provide a new and improved gaseous-discharge device that obviates the above-mentioned difliculties and extends the life of such tubes. These results are effected by trapping in the cathode end of the tube a substantial quantity of the material sputtered out of the cathode during the discharge between the anode and cathode. This trapping is preferably effected with the aid of an'appropriately disposed mesh screen, or filter material.

Other and further objects will be explained hereinafter and will be more particularly pointed out in the appended claims.

The invention will now be described in connection with the accompanying drawings Fig. 1 of which is a longitudinal section of a gaseous-discharge device constructed in accordance with the present invention; and

Figs. 2, 3, 4 and 5 are similar views of modifications.

A gas-filled device of the above-described character comprises an envelope or tube 3, as of glass, quartz, or any other suitable material, having a plurality of electrodes in the gas of the device. An anode electrode 4 may be supported within the tube 3 by a conductor 2 that a conductor 1 in spaced relation from the anode 4 within the gas of the tube 3. It is necessary for the utilization of the tube 3 as a source of illumination, that at least the region of the tube walls between the anode 4 and the cathode 7 be transparent. A source of voltage, such as a direct-current-charged capacitor, schematically represented by the terminals labelled and is connected between the anode 4 and the cathode 7 to serve as a source of energy for producing a discharge through the gas in the tube 3 between the anode 4 and the cathode 7. This discharge may be effected in any desired manner, as for example, with the aid of an auxiliary external trigger electrode 13. Other well-known discharging arrangements may also be used, with or Without external or internal trigger electrodes. The anode and cathode, moreover, may be of any desired type. For flash-illumination purposes, the cathode is preferably of the sintered cold-cathode type described more fully in United States Letters Patent 2,492,142 issued December 27, 1949 to Kenneth J. Germeshausen. In these Letters Patent, moreover, a preferred type of flashing circuit is illustrated. A cold cathode of this nature may be constituted of a substance such as tungsten, molybdenum or tantalum, uniformly sintered and bound together into a unitary mass with an oxygen-containing compound of, for example, barium, strontium or calcium, and upon which a relatively small cold-cathode spot is formed to produce the emission of electrons from the cold cathode at temperatures very substantially below the temperatures at which substantial thermionic emission may be produced from the cold cathode.

In the embodiment of Fig. 1, a mesh filter screen 5 is securedby any desired attaching means 12, such as, for example, an insulating ceramic cement, to an insulator 9 disposed at the base of the cathode 7. The insulator 9 is supported by a member 11 fixed to the conductor 1.

The screen 5 extends upward from the insulator 9 about the sides of the cathode 7 to envelope the same, and then extends outwardly beyond the upper end of the cathode 7 to the walls of the tube 3 as at 6. It is preferable that this cup-shaped screen 5 comprise a wire mesh of from about It). A cathode electrode 7 may similarly be supported by 0 of the filtering action. The portions of the cathode material sputtered from the cathode 7 during the discharge in the tube 3 between the anode 4 and the cathode '7 are violently driven by the before-described high instantaneous pressure produced by the discharge in a direction away from the region between the anode and the cathode and through the mesh screen 5 into the end of the tube 3 below the cathode 7, as viewed in Fig. 1. A substantial quantity of the sputtered material forced through the mesh screen 5 by the pressure produced by the discharge becomes trapped by the screen 5, and whenthe gas thereafter returns to the region between the anode and cathode, additional sputtered material is trapped by the screen and deposited thereon. The gas returning to the region of the tube 3 between the anode 4 and the cathode 7, therefore, does not carry back appreciable quantities of the sputtered material so that the walls of the tube between the anode 4 and the cathode '7 do not rapidly accumulate deposits of the sputtered material, but, to the contrary, remain relatively clean and clear for long periods of time. Since strong mechanical forces are set up during the discharge, the screen 5 and its supporting structure must be mechanically rigid. It is for this, among other reasons, that the wire mesh is preferred as a trapping means. To obviate the possibility of the discharge are from the anode 4 striking upon such a conductive wire screen 5, in view of the close proximity of the screen 5 3 to the cathode 7 and since portions of the screen may be closer to the anode than the cathode, the before-mentioned support 9 is constituted of insulating material in order to isolate the cathode 7 and the screen 5.

In some cases, wherethedischarge through thetube may be oscillatory,it may be desirable to employ identical cathode structures 5, 7,9 and 50, 70, 90, Fig. 5, at both ends of the tube 3, each cathode 7 and 70 serving alternately as ananode and a cathode. Such a construction also obviates the need for observing polarity when connecting the tube conductors 1, 20 to the circuit.

If desired, other types or traps or mesh filters may be employed, such as a glass-fiber woven mesh having strong mechanical properties. The use of .such an insulating mesh would permit-its directattachment tothe cathode. The filter mayalso be constituted of perforated metal or random-grouped metal fibers, such as steel wool. The trapping device, moreover, need not be mounted in the cup-shaped manner of Fig. ,1. If, forexample, a hollow cold cathode is employed, such as the tubular cathode 7 of Fig. .2, the mesh 5 may be substantially planar in shape, covering the lower end of the cathode 7. The hollow cathode 7 is illustrated as supported near its lower end by acurved terminal portion 14 of theconductor support 1.. In Fig. 2, an insulating member .9 in the form of a hollow sleeve surrounds the cathode 7 and prevents the discharge from striking on the outside surface of the cathode 7. The insulating sleeve member 9 extends longitudinally preferably above and below the cathode 7, and transversely very closeto the walls of the tube, effectively closing the space between the inner tube wall 3 andthe outer wall of'the sleeve member 9, thereby preventing sputtered cathode material from traversing that space. The screen or filter 5 is shown secured so as to cover the open end of the hollow cathode away from the anode. In this construction, the screen 5 may be attached or welded directly to thecathode support member 14 as at 16, since it is farther away from the anode 4 and is shielded therefrom by the upper end of the cathode 7, thus ensuring that the discharge will not strike to the screen 5.

Still a further arrangement of a sputter trap is shown in Fig. 4. The cathode 7 is shown surrounded by an insulating cylinder 9 open at both ends. The cylinder 9 is supported by a cylindrical'rnesh or perforated-metal trapping member 5 attached to the cathode conductor support 1 by a metal disc 15 that closes ofi the lower end of the member ,5. The mesh cylinder 5 may be attached to the insulating member 9 by means of the before-mentioned ceramic cement or by a clamp, not shown. The member 5 may, in turn, be welded to the disc 15 since, as in the structure shownin Fig. 2, the mesh screen 5 is farther. from the anode 4 than the cathode 7 and is shielded from the anode 4. The discharge will there fore not strike to the mesh cylinder 5. The space between the cathode'7 and the insulating member 9 must be sufiiciently large, say of the order of inch, more or less, to permit the gas in the tube 3 to be forced through this space and out through the mesh trap 5.

While the embodiments of Figs. 1, 2, 4 and 5 aredirected to cold-cathode gaseous-discharge devices, the invention is also useful with hot-cathode devices. In Fig. 3, for example, a screen '5 of the type previously described in connection with the embodiment of Fig. l is shown provided with a heated filament-type cathode 7' in the gas-discharge lamp 3. The specific trap mechanisms of the other embodiments, moreover, may equally well be employed in the hot-cathode tube of Fig. 3, and, indeed, the sputter traps shown in each figure may equally well be embodied into the devices of the other figures, as well as into other types of tubes.

Through the tubes-of Figs. .2, 3, 4 and 5 have been shown unprovided with third or further auxiliary electrodes, such as the trigger electrode13 of Fig. 1, it is to be understood that they,,may, if desired, be operated with such additional electrodes, as is well known.

The invention, moreover, is not limited, in its broadest aspect, to flash tubes or illumination-producing tubes, though it is of great utility in connection therewith, since the trapping feature of the present invention is useful wherever it is desired to prevent the depositing of sputtered material in the region between the anode and cathode of an electric-discharge device. The invention is also of utility with discharge devices operated with alternatingcurrent, as well asdirector pulsating-current voltages.

Further modifications will occur to those skilled in the art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A gas-filled device having a plurality of electrodes in the gas of the device comprising an anode and a cathode comprising material portions of which, during a discharge between the anode and the cathode, sputter out of the cathode and are drivenby the pressure of the discharge in a direction away, from the anode, and means for trapping a substantial quantity of the sputtered material to prevent its traveling into the region of the device between the anode and cathode.

2. A gas-filled device having a plurality of electrodes in the gas ofthe device comprising an anode and a cathode comprising material portions of which, during a discharge between the anode and the cathode, sputter out of the cathode and are driven by the pressure of the discharge in adirection awayfrom the anode, and mechanical filter meansfor trapping a'substantial quantity of the sputtered material to prevent its traveling into the regionbetween the anode and cathode.

3. A gas-filled device having a plurality of electrodes inthe gas of the device comprising an anode and a cathode comprising material portions of which, during a discharge between the anode and the cathode, sputter out of the cathode and are driven by the pressure of the discharge in a direction away from the anode, and a mesh disposed adjacent the cathode for trapping a substantial quantity of the sputtered material to prevent its traveling into the region of the device between the anode and cathode.

4. A gas-filled device having a plurality of. electrodes in the gas of the device comprising an anode and a cathode comprising material portions of which, during a discharge between the anode and the cathode, sputter out of the cathode and are driven by the pressure of the discharge in a direction away from the anode, and a cup-shaped mesh disposed adjacent the cathode for trapping a substantial quantity of the sputtered material to prevent its travelinginto the .region of the device between the anode and cathode.

5. A gas-filled device having a plurality of electrodes in'the gas of the device comprising an anode and a cold cathode of the type upon a surface of which a relatively small cold-cathode spot is adapted to be formed to produce the emission of electrons from the cold cathode toward the anode at temperatures very substantially be low the temperatures at which substantial thermionic emission may be produced fromthe cold cathode and comprising 'material portions of which, during a discharge between the anode and the cathode, sputter out of the cathode and are driven by the pressure of thedischarge in,a direction .away from the anode, and means for trapping a substantial quantity of the sputtered material to prevent its travelinginto the region of the device between the anode and cathode.

6. A gas-filled device having a plurality of spaced electrodes in the gas of the device, each electrode comprisingmaterial portions ,of which, during a discharge between the.electr.odes, sputter out of the electrodes and are driven by the pressure of the discharge away from the space between the electrodes, and means disposed adjacent each of the electrodes for trapping a substantial quantity of the sputtered material to prevent its traveling back into the space of the device between the said electrodes.

7. A gas-filled device having a plurality of electrodes in the gas of the device comprising an anode and a cathode disposed near a predetermined part of the device and comprising material portions of which, during a discharge between the anode and the cathode, sputter out of the cathode and are driven with a portion of the gas of the device by the presure of the discharge into the said predetermined part of the device, and means disposed adjacent the cathode for trapping a substantial quantity of the sputtered material to prevent its traveling with the said portion of the gas into the region of the device between the anode and cathode upon termination of the discharge.

8. A gas-filled device having a plurality of electrodes in the gas of the device at least one of which, disposed near a predetermined part of the device, comprises material portions of which, during a discharge between the electrodes, sputter out of the said one electrode and are driven with a portion of the gas of the device by the pressure of the discharge into the said part of the device, and a conductive mesh disposed adjacent the said one electrode for trapping a substantial quantity of the sputtered material to prevent its traveling with the said portion of the gas into the region of the device between the electrodes upon termination of the discharge.

References Cited in the file of this patent UNITED STATES PATENTS 2,030,435 Feshe et al. Feb. 13, 1936 2,300,997 Van Horn Nov. 3, 1942 2,494,916 Van Horn Jan. 17, 1950

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