US3024382A - Gas cushion keep-alive electrode - Google Patents

Description

March 6, 1962 D. L. SCHAEFER ETAL 3,024,382

GAS CUSHION KEEP-ALIVE ELECTRODE Filed Sept. 4, 1959 INVENTORS DONALD L. SCHAEFER JOHN E. WHITE BY A ITOR/VEYS United States are-tit 3,924,382 Patented Mar. 6, 1962 This invention relates to gaseous discharge devices, and more particularly to the rapid ignition, and mainvtenance of the main discharge of a cold cathode gaseous device by anauxiliary electrode.

Gas or vapor-filled electron tubes may generally be classified as to the type of cathode employed, namely hot or cold. Each type may vary as to the number of .electrodes and further, the cathods themselves may be either liquid or solid. These electron tubes find their principal use as rectifiers, voltage regulators, control devices, switches, sweep circuit oscillators and in recent times as modulator and T.-R. tubes within radar systems. Cold cathode tubes such as those employing a mercury pool afford certain advantages over hot cathode tubes. Certain vapor or gas filled tubes are provided with keepalive electrodes which continuously maintain an arc to the cathode. Suchkeep-alive electrodes are necessary in single anode mercury-cathode units where the tube would otherwise extinguish during the negative half cycle of an applied AC. voltage, or where the anode voltage was momentarily interrupted, or where the anode current is pulsed. Ignition methods such as the production of a high field by an auxiliary electrode closely spaced above a mercury cathode pool has proved impractical because of the waves and fluctuations in the mercury pool level of liquid cathode tubes, and the erosion of cathode materials in solid cathode tubes.

The desirable electrical characteristics of cold liquid cathode gas or vapor tubes can be put to many useful purposes as for example, in pulse modulator tubes and T.-R. tubes where a single anode is employed since high current pulse application is possible and the cold cathode tube is not subject to the current density limitations of thermionic cathodes in application. However, before this type of cold liquid'cathode tube may be used successfully, a method for igniting and maintaining a cathode spot is essential.

It is therefore an object of this invention to provide a device for igniting and maintaining a cathode spot on liquid cathodes of gas or vapor-filled electronic tubes.

Another object is to provide a device for creating a continuous supply of electrons from a liquid cathode sufiicient to ignite the main are of a tube.

A further object is to provide a relatively low current .drain device for the ignition of a liquid cold cathode gas tube.

Other objects are to provide an electrically and mechanically simple, efiicient, inexpensive and reliable device for the ignition of liquid cold cathode gas tubes.

Other objects and advantages will be apparent from the following description of embodiments of the invention and the novel .features thereof will be particularly pointed out hereinafter in connection with the appended claims.

In the accompanying drawings:

FIG. 1 is a cross-sectional diagram of a liquid cathode tube illustrating an embodiment of the invention; and

FIG. 2 is a perspective, illustrating another embodiment of the invention.

In the embodiment of the invention illustrated in FIG. 1, a closed glass envelope 1, or an envelope of, any suitable material, contains a vapor or gas filling, an anode 2. supported therein by conducting rod 3, and a liquid mercury pool cathode 4 or a gallium pool disposed at the base of the envelope or tube opposite the anode. Electrical connection from outside the envelope is made to the anode through the electrical conducting rod 3 which extends from, and'is secured to, the anode and passes through that portion of the envelope opposite and remote from the cathode for external wiring thereto. Conducting rods 5 and 6 extend through a portion of the base of the envelope into the liquid cathode 4, and electrical connection from the exterior of the envelope is made to the cathode by means of these rods. The ends of the rods disposed within the cathode project into the cathode from the base of the envelope and extend upwardly to an area well below the surface of the cathode. Electrical lead-in rods 7, and 8 extend and project through opposite vertical side walls of the envelope in a direction normal to the sides at points intermediate between the surface of the cathode and the anode, and their inner end portions are threaded. Since the tube is vapor or gas filled, the rods 3, 5, 6, 7 and 8 are peripherically bonded to the envelope wall through which they pass so as to hermetically seal the envelope which is evacuated and filled with a suitable ionizable gas or vapor, such as mercury. Retaining nuts 10 and 11 are threaded on the end portions 9 of each of the lead-in rods 7 and 8 and a sickle shaped tab 12 is supported between the tightly abutting faces of each pair of these nuts. The concave portions of these tabs face each other and meet any spring-like, electrically conductive, heat resistant material, such as for example. molybdenum. Each tab 12 may be afiixed to its lead in rod in any suitable manner providing the end of the tab so afiixed is permanently tightly confined against movement. A wire 13 of a material which will withstand high temperatures, having intermediate of its ends a horizontally undulatory portion 13a, such as of S shape is welded or otherwise firmly fixed to the free ends of the tabs to connect them. The tabs 12 support the wire 13, which may be, for example, of tungsten or molybdenum just above and spaced slightly from the mercury cathode, with the plane of the 8 portion of the wire parallel to the cathode surface, and by reason of the arouate form and resiliency of the tabs, is movable a short distance toward and away from the cathode surface when subjected to opposing forces. The S shape of the wire 13, by giving extra concentration of weight in a local zone of the wire, gives the wire freedom of motion and causes the 8 portion of the wire to sag in the direction of the cathode surface.

When a DC. potential is applied, as by battery 14, between the keep-alive wire 13 and the mercury cathode, the keep-alive wire being positive with respect to the cathode, the keep-alive wire automatically adjusts itself in spaced relation to the cathode surface under the action of two oppositely directed forces. The electrostatic force created by theapplied DC. potential tends to pull the wire in the direction of the mercury cathode, but as the wire approaches the cathode surface arcing ensues be tween the wire and the cathode, and a cathode spot forms on the cathode surface directlyopposit'e the wire. With the formation of the arc, a vapor blast or a Tanberg effect occurs which applies a repulsive or upwardly directed force to that portion of the wire directly above the cathode spot. The electrostatic and the vapor blast forces act on the wire in opposing directions and the Wire therefore automatically assumes a spaced relation above the cathode surface whereat these forces are equal and opposite so that the keep-alive wire is in mechanical and physical equilibrium. Under these conditions, an arc is continually maintained between the keep-alive wire electrode and the liquid cathode. The spacing between the keep-alive wire electrode is thus automatically adjusted to maintain the arc. If the DC. potential should decrease or temporarily extinguish the keep-alive wire would then move toward the cathode until either the spacing between the wire and the cathode was sufiicient to reignite the are or until its movement toward the cathode was mechanically limited by the tabs 12 and then when the DC. potential was again applied the arc would reignite and the wire 13 would again be repelled from the cathode surface by the vapor blast until it again assumed its equilibrium or firing position.

It has been found that successful operation under the above conditions can be maintained using a 0.0008 inch tungsten wire 13 tabed with a 0.001 inch thick tab 12, 0.005 inch wide and about one millimeter long. The keep-alive arc provides the necessary vapor ionization, though localized, in the tube so that when a voltage is applied between the main anode 2 and cathode 4, a main discharge or conduction will be accurate, reliable and immediate.

A third electrode, as for example a control grid (not shown), may be added to the above described tube embodiment. This arrangement is the equivalent of a thyratron tube with a cold liquid cathode and is extremely useful for pulse-modulation applications since the anode current exceeds that of the solid cathode thyratron.

In an embodiment of another keep-alive electrode according to this invention, which is illustrated in FIG. 2, a metallic horizontal support extends across the tube chamber, with its ends passing through and sealed to opposite walls of the tube 10, and within the tube chamber it has two substantially parallel. depending metallic hangers 21 and 22, spaced from each other. The free ends of the hangers are bent back on themselves to form hanger eyes 23 and 24 whose openings are axially aligned with one another and receive therein and support therebetween for axial rotation, a cylindrical metallic rod 25. Disposed in cross-wise relation to the cylindrical rod 25 and suitably secured or spot welded at the approximate center of the rod 25 is a metallic vane 26. The vane is secured to the rod at approximately the vanes center of gravity 27, so that the vane is balanced about the point of contact, and since rod 25 is free to rotate the vane 26 can pivot about the axis of rod 25 somewhat like a scale balance. One end portion of the vane 23 is spoon shaped with the concave side facing upwardly, such as substantially in the direction of the support 20, while the opposite end portion 29 of the vane is bent upwardly and laterally as at 29, to form an offset end 29a which is approximately parallel with the main body of the vane. This upwardly offset end of the vane extends between and beyond the arms 30 and 31 of a U-shaped member 32, that are perpendicular to the plane of the vane and substantially parallel to the hangers, thereby limiting the pivoting motion of the vane to within selected limits. One arm of the member 32, as for instance arm 31, is extended and bent, and then attached, as by spot welding, to one of the hangers 22 for support. This entire keep-alive structure is supported within the closed gas-filled envelope or tube in so that the spoon portion 28 of the vane in its lowermost position of travel is disposed just above the surface of the liquid cathode.

The operation of this balanced vane keep-alive is similar to the operation of the first described embodiment, except that the vertical travel of the spoon or electrode is limited by the U-shaped member 32 and a larger electrode (spoon) surface is employed. The component members of this last described embodiment preferably should be of tantalum or tungsten or a combination thereof. The DC. potential is applied between the cathode and the ends 33 and 34 of the support outside of the tube envelope. Since all the keep-alive components are electrical conductors, this DC. potential also exists between the vane 26 and the cathode.

The keep-alive devices described herein when used with liquid cold cathodes are means to supply a virtually unlimited electron source for tubes such as pulse modulators, and these cold cathode tubes are also valuable where high current pulse applications are required. Comparison with competitive devices such as thyratrons, ignitrons and excitrons will bear out the advantages of this keepalive electrode. Ignoring the simplicity and the lower cost of operation of the gas cushion keep-alive, it is capable of withstanding overload and fault currents over those of a thyratron. Commercial thyratrons will generally deliver about 1 ampere peak per watt of cathode heating power while the gas cushion keep-alive can operate from a volt source at 10 milliamperes. Comparison with an ignitron is quite favorable, since a tube employing the keep-alive embodiment of this invention has all the advantages of high peak anode currents, with low control power of a grid as compared to the tens of amperes at hundreds of volts required by the ignitron. Comparison with the excitron or multianode rectifier shows immediately the advantage of substantially lower excitation power and moreover, the keep-alive restrains the motion of the cathode spot to a small area directly below the keep-alive electrode, so that the major problem of excitron and multi-anode tube design, that of keeping the cathode spot off the tube walls, is avoided.

It will be understood that various other changes in the details, materials and the arrangements of parts which have been herein described and illustrated in order to explain the nature of this invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

We claim:

1. A gaseous electric discharge device comprising a closed envelope containing a gas filling and having therein spaced relation to one another, an anode and a liquid cathode with a surface exposed toward said anode, an auxiliary electrode device disposed in said envelope between the anode and said cathode surface but with a part thereof in close proximity to the cathode, that is movable toward and away from said exposed cathode surface under relatively small vapor blast and electrostatic forces but limited against contact with said cathode surface whereby when a potential is created between said electrode part and said cathode surface, said electrode part will be in mechanical physical equilibrium in spaced relation to the cathode surface due to the opposing forces created by the electrostatic attractive force pulling said electrode part toward the cathode and the opposing vapor blast rcpulsing force from the cathode facilitating thereby the establishment and maintenance of the main discharge between said anode and said cathode.

2. The device according to claim 1, wherein said closed envelope contains mercury vapor and said liquid cathode is mercury.

33. The device according to claim 1, wherein said closed envelope contains another electrode disposed between said auxiliary electrode and said anode for control of said main discharge.

4. The device according to claim 1, wherein said auxiliary electrode is a bar physically supported and balanced for pivotal movement whereby its ends are movable toward and away from said exposed cathode surface.

5. The device according to claim 4, wherein an end of said bar has a large surface area directed substantially toward said cathode.

6. A gaseous electric discharge device comprising a closed envelope containing a gas filling and having therein in spaced relation to one another, an anode and a liquid cathode with a surface exposed toward said anode, an auxiliary electrode device disposed in said envelope between the anode and said cathode surface but with a part thereof in close proximity to the cathode, said auxiliary electrode being a relatively fine wire supported at its ends to close proximity to the cathode, that is movable toward and away from said exposed cathode surface under relatively small forces but limited against contact with said cathode surface whereby when a potential is created between said electrode part and said cathode surface, said electrode part will be in mechanical physical equilibrium in spaced relation to the cathode surface due to the opposing forces created by the electrostatic attractive force pulling said electrode part toward the cathode and the opposing vapor blast repulsing force from the cathode facilitating thereby the establishment and maintenance of the main discharge between said anode and said cathode.

7. The device according to claim 6, wherein said fine wire has an undulatory portion plane which is substantially parallel to said cathode surface.

8. The device according to claim 7, wherein said undulatory portion of said wire is S shaped.

References Cited in the file of this patent UNITED STATES PATENTS

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