US1995176A - Electric discharge apparatus - Google Patents

Description

March 19, 1935.- A. GLASER ELECTRIC DISCHARGE APPARATUS Filed 001;. 17, 1952 i q 0e n ta m w a Va A .mu .6 M; H

Patented Mar. 19, 1935' UNITEDIST AraNr orricr. T

ELECTRIO DISCHARGE APPARATUS August Glaser, BerlineFrohnau, .Germanyyassigner to General Electric Company, a corporation of New York Application October 17, 1932 Serial No. 638,235

In Germany October 21, 1931 2 Claims.

The presentinvention relates to electric discharge apparatus, more particularly to hot cathode devices which contain gas or vapor and are current is caused to a large extent by the pres.-

enceof positive ions in the region of the anode which hold over from'the forward or positive half-cycle.

7 An object of the present inventionis to provide an improved tube structure which causes an immediate absorption or neutralization of the positive ions during inverse so that arc back is precluded. A tube improved in accordance with the invention is thus capable of withstanding oonsid e'rably higher voltages than prior art devices, with consequent increased output and efficiency.

'In carryingout this object, an auxiliary electrode is provided near the anode and is charged to a higher negative potential than the anode during the inverse portion of the alternating current cycle in order to attract the positive ions away 7 from the anodeand neutralize them. There is also provided a current-limiting resistance in series with the auxiliary electrode to prevent the latter f m nsover the function of the main The inven anode during the positive half-cycle. tion will be more fully understood when reference is made to the following description and the accompanying drawing in which Fig. 1 shows diagrammatically the improved tube and an energizing circuit, while Fig. 2 illustrates a portion of a modified form of tube.

In the drawing, numeral 1 designates the envelope of a tube containing a cathode which is shown as an indirectly heated member, a platelike anode 2, an auxiliary'electrode 3, and an electrostatic control member 4. The indirectly heated cathode is generically illustrated as a fila-v mentary heater 5 in heat-responsive relation to a fiat plate 6 which is electrically connected to one leg of the filament and preferably is coated with electronically active material to constitute the cathode proper. The electrodes 3 and 4 conveniently are made of'perforated material and extend transversely across the envelope, although it will be understood that these electrodes, as well as the anode 2 and the cathode 6, may take on any suitable configuration e. g. concentric cylinders; etc., depending upon the desired characteristics of the tube. The member 3, referred to hereinafter as the .auxiliary electrodef, is positioned near the anode for reasons which will appear presently. The envelope 1 contains an ionizable, medium, such as inert gas (helium, argonor'the'like) or mercury (not shown) having a pressure under operating conditions suf1-- cient to support an arc-like discharge at the impressed voltages. i 7

The heater 5 is energized by a source of alternating current through thetransformer .7, and

. thev anode is .connected to asource of current,

preferably alternatingcurrent, through atransformer, 8. One end of the secondary of transformer 8 isconnected through a load broadly indicated by rectangleQ to heater 5 and'cathode 6, while'the other terminal of the transformeris connected to the auxiliary electrode 3 through a fairly high impedance l0, resistance -or the like, also generically indicated by a rectangle. The anode 2 is connected to an intermediate tap 11. on the transformer, secondary. The grid or electrostatic control member 4 may be connected to'a source of control impulses.

In operation, when the charge on the grid 4 is sufficiently positive or less negative, an arc or, glow dischargewill be produced in the tube due. to the potential applied to the'anode 2. This are is caused by the cumulative ionization of the gas or vapor in. the tube, and when once the arc has, started, the grid fl loses control unless a prohibitory negativecharg'e is applied thereto. This loss of control extends through the positive half-cycle of the alternating current voltage. When the transformer voltage reverses so that the anode 2 becomes negative with respect to the cathode and the arc goes out,-control is restored to the grid which then determines when the arc will start during the next positive half-cycle.

During the positive half-cycle when current flow is established, the gas or vapor becomes ionized and the positive ions formed thereby, also the electrons emanated by the cathode 6, serve to reduce the impedance of the tube so that a large current flows at relatively low voltages. It has been found that when the voltage of the energizing source reverses,'i. e. during the negative half-cycle, some of the positive ions hold over fromthe previous positive half-cycle and tend to cause reverse currents, thereby reducing the translation efficiency of thedevice and in extreme cases, causing damage to the tube.

In order to eliminatethese positive ions and in accordance with my invention, there is provided the auxiliary electrode 3 which as stated hereinbefore, is connected to one of the outer terminals of the transformer. During the negative half-cycle, this electrode becomes more negative than the anode when considered with respect to the cathode. It is apparent that under these conditions, the highly negative electrode 3 will immediately absorb the positive ions which reside in the region of the anode at the beginning of the negative half -cycle and consequently, will prevent ionization of the gas or vapor taking place when the anode is negative with respect to the cathode. In order that the auxiliary electrode 3 may not itself give rise. to the, production of positive ions on account of its'high' potential with respect to the anode 2 and the; cathode 6, there may be provided in the, auxiliary electrode circuit, a current-limiting resistance 10. The space between the auxiliary electrode 3, and the anode 2 is preferably less than the free mean path of electrons in the space, which further re duces the possibility of glow discharge occurring between electrodes 2 and, 3. V

It is apparent that since the auxiliary electrode 3 immediatelyandfcompletely removes the positive ions left in the envelope when thevoltage of h e er in cu rent ourc o es he er voltage axis and starts on the inverse halzf cycle, mp dance Qff u which w s n i ere ably reduced "duringthe formation of the are or glow discharge, is now. increased and remains at a; high value I throughout the remainder of'the cycle. Consequently, the tube efilciently conducts current in the positive direction, i. e; when the anode is positive, but constitutesa substan-' tially open circuit whenthe anode is negative, It is also apparent that since the auxiliary electrode 3" is connected to the same secondary winding as theanode 2, the volta'ges applied to! these two'electrodes are inphase, so'that the auxiliary electrode 3 becomeshighly negative with. respect to the cathode 6 at the samemoment that the anode 2 is also negative. Since this phase relation remains the same, the frequency of the alternating voltage applied to the anode may be increased indefinitely without any substantial reduction of the efficiency with which the auxiliary I electrode operates. In somecases, it may be ad: vantageous to provide inftlie auxiliary electrode, circuit, an adjustable direct current voltage, ob-'' tained, for example, from abattery (not shown) in' order that the time in the voltage cycle at. P which the auxiliary, electrode absorbs the positive ions may be more accurately determined. However, it has been found that ordinarily, the auxiliary electrode may be connected directly to the transformer secondary through the non-adjustable high resistance 10.

'While I have described my invention in connection with an electrostatically controlled arc discharge device employing an indirectly heated cathode, it is to be understood that the invention is not limited to this structure but applies equally wellto a two-electrode rectifier without a control member and also to a device which employs a directly heated or even a cold cathode.

In Fig. 2, the'auxiliary electrode takes the form of a hollow cylinder 12 secured in the glass stern 13 ofthe envelope 1 in any suitable and wellknown manner, 'Ihe cylinder 12 is provided at its endfacing the cathode with a perforated metal plate 14 which, together with the cylinder, serves the purpose of absorbing the positive ions held over from the positive half-cycle. Leading-in conductorslfi and 16 may be taken respectively from the anode and the cylinder to.theexterior, for -connection tothe secondaryof an energy sup ply transformer as explained hereinbefore.

' What I claim as new and desire to secure by Letters Eatent of the. United States, is:

1. In combination, an, electric discharge device comprising an envelope containing a cathode, ananode and an inert gas at apressure sufii cientto support anarc-like, discharge at the im: pressedvoltages, an auxiliary, electrodepositioned, in the region of said anode, an alternating, cur rent supply. transformer, the outer terminals of said transformer being connected-respectively to, said cathode and said'auxiliary electrode, and a connection. between an.intermediate tap on said" AUGUS

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