US2619593A - Pulse energized gas tube circuits - Google Patents

Description

Nov. 25, 1952 1.. MALTER 2,619,593

PULSE ENERGIZED GAS TUBE CIRCUITS Filed Jan. 2, 1951 INVENTOR L ours MALTER ATTORNEY and-ionizing thetgas.

Patented Nov. 25, 1952 um TED STATES PATENT OFFICE,

Louis lMa'lter, Princeton, N. J assignor 'to Radio Corporationfof America, a. corporation l'offDela- Application January 2, 1951, Serial ,N0.."203,923

14 Claims. 7 1

This inventionrelates to improvements in gaseous electron tube systems, an particularly to :animproved method of and apparatusior-opcrating gaseous electron tubes. H Itiswell known in theelectrontube art that the limiting effect of space-charge on thecur-rent that will now in an, evacuated tube canbe overcome byadding asmall quantityof gasto thetube,

7 If a sufficiently #high voltage isapplied between theemitting andrcol-lecting electrodes .in the tube, the gaswill be ionized by electron bombardment of the gas molecules,

thereby developing positive ions which will neutralize the negative space charge of the electrons. The combinedcloud or plasma of ions and electrons will act as an excellent conductor, allowing thetube current to rise veryrapidlyuntil the full electron-emitting capacity-of the emitter is being utilized.

While the :phenomenonbriefly described above has considerable practical utility, there are ,several. characteristics of gas-filled tubes which heretofore have imposed limitations on their use.

For one thing, a certain minimum voltage is requiredto ionize the gas inthe tube. That is,-in general, a certain amount of energy must be given to an atom or moleculein order toremove an electron therefrom. In the case of a gas tube, this means that the ionizing (bombarding) electrons must be given a certain minimum velocity to sustain ionization. To give the ionizingyelectrons this minimum velocity, a corresponding minimum potential or are drop must be maintained between an electron emitterelectrode and 'anelectron collectorelectrodeimmersedin the gas. In conventional gas tube systems, this are dropgis wasted in'any case where aprincipal objective is to transfer voltage from a source to a load with the 1east possible voltage loss in the transfer circuit.

Another difiiculty is the problemof controlling gas tube current efliciently. In a conventional vacuum tube, acontrol electrode placed between the emitting and collecting electrodes provides a very efficientmeansof controlling the :tube current. Avery small change in the control electrode voltage will have a relatively large effect on tube current, it being possible to vary the tube current smoothly and continuously within relatively wide limits simply by varying the control electrode voltage.

In the case of the conventional gas tube, however, a:s.0mewha.t difierent situation exists. It is found-that a control electrode in a conventionally operated gas tube has only a ,trigger type con-- trol action. The .proper amount-of negativeivolit- ,2 age on such control electrodew-ill prevent tube current from 'fiowing, and tube current liow '.can be started .by a suitable decreasein the negative control-electrode voltage. However, once theco'nventionally operated gas tube begins to conduct current, the control electrode loses. practically all control, and the tube current'becomes substantially independent of the control electrode -voltage.

In a copending application of. "0. Johnson, Serial No. 185,745, filed September'ZO, 1950, assigned-to the assignee of the present invention, there is described a gaseous electron tube system in which a space charge neutralizing .plasma is generated 'by. an auxiliary ionizing discharge of electrons. In saidcopending Johnson application, a system is described wherein an auxiliary emitter electrode provides the ionizing'currjent. With this arrangement, two very important .advantagesare attained.

First, it is found that very high current can be passed between the main emitter and collector electrodes at potentials 'far below those requireolf'to ionize the gas. Second, it .is found that the current fiowbetween main emitter and collector can be controlled in various Ways, one of which is by means of a-control electrode similar to that used in the conventional vacuumtube.

'Wh'ile gas tube systems of the. type just describedhave many useful and important applications it has been found that random oscillatory voltages originate in the plasma when the latter,

is maintained'by a continuous auxiliary discharge.

In some instances, the e'iiect of these oscillatoryvoltages-on'the'mainftube current is objectionable, particularly in the case where the gas 'tubeused has only one emitter electrode. 7

It is a general object of the present invention to provide an improved method of and apparatus for operating gaseous electron tubes.

A more specific objectofthe invention is the provision of a method .of and apparatus :for op erating aigaseous electron tube under conditions.

such that relatively 'high currentcan be passed through the tube at a voltage-lower than-the are drop required to sustain ionization ofthe gasfin the tube.

A further object of the invention is :thelprm' of an improved method of and apparatus ior. separating the functions of gas ionizationfandi high current discharge in a gaseous' electron 'tube system in a. manner such that a substantially noiseless current can be drawn through the as tube.

In accordance with the invention, the foregoing and other related objects and advantages are attained in a method and system wherein space charge neutralizing ions are generated in a single emitter gas tube in spaced bursts by applying suitable voltage pulses between the emitter and another tube electrode. The plasma so created will conduct very high, substantially noiseless currents at voltages considerably below the gas ionizing potential. Furthermore, this current can be substantially continuously controlled in a number of different ways as, for example, by means of a control electrode.

A more complete understanding of the invention can be had by reference to the following description of illustrative embodiments thereof, when considered in connection with the accompanying drawing, wherein:

Fig. 1 is a schematic diagram of a gaseous electron tube circuit illustrating the general principles of the invention,

Fig. 1a is a sectional view of a modified form of gas tube,

Fig. 2 is a schematic diagram of a grid-controlled gas tube system arranged in accordance with the invention,

Fig. 3 is a schematic diagram of a gas tube rectifier system arranged in accordance with the invention, and

Fig. 4 is a schematic diagram illustrating application of the principles of the invention to a frequency modulated wave detection system.

As was previously stated, an ordinary gas tube operated in the conventional manner does not have as much utility as might be expected. Consider, for example, the gas tetrode tube Hl shown in Fig. 1. This tube, which may be a commercial type 2050 tube for example, has an electron emitter or cathode I2, usually heated by a filament (not shown), a control electrode 14, a shield electrode 16, and a collector electrode or anode [8.

In the usual case, the anode l8 would be connected to the cathode l2 through a work circuit including a load device and a. source of voltage at least-equal to and usually greater than the arc drop required to sustain ionization of the tube gas. The shield electrode I6 usually would be operated at the same voltage as the cathode 12. The control electrode l4 normally would be at a potential sufficiently negative to keep the tube cut ofi, and the tube would be fired by decreasing the control electrode voltage.

Once the tube had been fired, the electrode [4 would lose control of the tube current. This loss of control is believed to come about from the fact that positive ions collect and form a sheath around the control electrode. This sheath builds up to a thickness such that, at the outer boundary of the sheath, the negative control electrode voltage is balanced by the positive field from the sheath. The main part of the discharge is thereby shielded from and unafiected by the control electrode. If the control potential is increased in an effort to restrict the main discharge area by increasing the sheath thickness, the result is a temporary increase in potential drop through the restricted area. This causes an increase in electron velocity and an increase in ionization, with the result that the sheath density increases without appreciable change in the sheath thickness.

In the conventional arrangement Just described, the work circuit voltage must initially be high enough to cause ionization. Even after ionization occurs, the arc drop between the work circuit electrodes must be kept high enough to sustain ionization. The voltage required to sustain ionization in the tube is, of course, wasted as far as the load is concerned. Frequently it would be very advantageous if the high currents characteristic of a gas tube could be obtained with a voltage loss of, say, one volt or less in the tube. Furthermore, if the work circuit voltage could be reduced, then the electron velocity changes which interfere with the control electrode influence on the tube current might be eliminated.

In Fig. 1 of the drawing, there is shown a circuit with which certain of the basic principles of the invention have been tested and established.

In the circuit of Fig. 1, a pulse generator 20 is connected to apply voltage pulses between the anode l8 and the cathode l2 of the tube ID. The shield electrode [6 is connected in a work circuit which includes a load device 22 (e. g. an ordinary resistor), a voltage source shown as a battery 24,.and the cathode l2. The control electrode I4 is allowed to float in this circuit.

Specific example of suitable pulse sources are given hereinafter. For the moment, it will sufiice to state that the pulse source 20 should be adapted to provide pulses of amplitude at least suflicient to ionize the gas in the tube l0.

In the circuit of Fig. 1, the pulses applied be tween the anode l8 and the cathode 12 will ionize the gas in the tube l0. It has been found that the conductive plasma generated by such pulses will permit a work circuit current of the order of milliamperes to fiow from the cathode l2 to the shield electrode IE, it being noted that the latter is serving as an electron collector electrode in the circuit of Fig. 1. Currents of this order of magnitude have been obtained with a voltage drop between the shield l6 and the cathode l2 of less than 0.1 volt.

In the circuit of Fig. 1, it is not feasible to control the Work circuit current flowing to the shield electrode It by means of the control elec-' trode [4 since the control electrode l4 does not have the proper configuration. If, however, as shown in Fig. 1a, a tube Illa is provided with a mesh-type grid electrode 14a between the cathode l2 and the shield or collector I6, the current to the collector readily can be controlled by a voltage applied to the grid Ma.

It might seem that pulsed ionization of the tube gas would provide a pulsating work circuit current of comparatively limited utility. However, due to the behavior of the ion-electron plasma, it is found that a substantially continuous work circuit current can be drawn through a pulse generated plasma under suitable conditions. This is possible for two reasons.

First, when ionizing current fiow through a gaseous electron tube is cut off, a finite time is required for the plasma to decay (i. e. removal of ions and electrons by diffusion, etc.). This decay time is primarily a function of the type of gas involved and the gas pressure.

Therefore, it can be seen that it should be possible to pass current through a decaying plasma even though the ionizing current has been interrupted. Even so, one might assume that the amplitude of the current drawn through a decaying plasma would decrease in accordance with the plasma decay curve It has been found, however, that the work circuitacurrentzis: not; a continuous sfunction; o1 plasmas densi va. Thatis; tier .a-a ivc vol a e ctweenthe work circuit electrodes 12,; t5; in .E s. he urrentrthat; wfllficw: thee-work circuit will: be propo onal to plasma ensity. n y; up to. a. certa nncint For; reater plasma densities. he work-. ir uit urrent willno f a but ill. have a; ubstan ally. nstant: ndependent of plasma density. Thereiorfi; i the on manulsesare large enouah and are re at at.-.-a hi henoll xh rate, atheworkcircu-it current canhbea continuous; current substantially unafiectedby the ionizing pulses. Also, the shorter the duration of ionizing. pulses, the less, chance there will be of generating plasma noise that might-interfere, with. the work circuit current.

While the plasma noise phenomenon just referred to1isnotentir 1yunderstood, it: s. nown that'masclong as ionizing currentis flowing, the voltage-drop across the plasma (between. the ele'cimodes carrying theionizingcurrent rises and.falls,rapidly,.and in a more or less. random fashion. This is thought tobe due, .in par-t, to the fact that as soon as lasma. is created theionizing current is able to flow at a. lower voltage,.,similar to the work circuit current flow. he plasma then may begin to decay, causing thevoltagebetweenthe ionizing electrodes to go up and repeating the ionizing process. In any event,,'it,isgknown that random fluctuations can be detected :in many instances in the current drawn through a continuously enerated. plasma. whereasthey are notfoundin the current drawn through a decayin plasma. Therefore, if ionizing current is passed through the gas invery shortsharpfbursts, followed by a relatively long decay, time, plasma, noise can be keptv at a very lowlcvel;

As was stated, the plasma decay time is a unction of the yp .ofg in he tube and h gas pressure. Therefore, it is not possible to state absolute values for the pulse repetition rate and" pulse amplitude required for continuous'work circuit current in all cases. However, a pulse amplitude, say, 100 percent greater than the arc drop required to sustain ionization, coupled-with a pulse rate such that the interval between pulses is, say, 60 percent less than the time required for complete plasma decay, ordinarily willsuffice. It will of course, be understood-that these percentages are intended to be illustrative 'and are not to be taken as absolute limits.

' Althoughthe voltage between the Work circuit electrodes will lee-much lessthan the arc drop required to sustain ionization, it is not essential that the work circuit voltage sourceitselfb so limited." Assume-tor example, in the circuit of Fig. 1 that the ionizing arc drop required for thesgas in the tube Idis 25 volts, and thatthe voltageofxthe source 24 is 100 volts. Assume also that; the-pulse generator 29 is disabled. Under these-circumstances, it has been found that thetube 1.9 will operate in rather conventional manner, with avoltage drop of about 25 volts, between the=emitter ll and-the collector. it, and WithIhB remainder of the source voltage appearingacrossthe1oad22. Now. if pulses of amplitudegreater than 25' volts and of repetition rateproperly correlated with the plasma decay rate are applied between the anode ltand the emitter itw l e found that. the, volta betweenthe collector 6 and the emitter l2. will dronto a very ow a ue. ay ofthccrdcr. of 0.1.vo1t, as p usly escribe withnra tica ly a... capacitor 48,;,in shunt with which may; I beech rodeor. rod 5; by; Q QQU W F new; -df. ohal ol l ctrode. 9 rovide djacen to h m tter 3 o eceive. on n cu 'c r om h m t r I3. Thisclcctrodc l -mav ompr sc wo o s di ed n; pn siter dcscf.andaral e th he emitter 3;- hilcthctubc shQ F g. li o. ould. be su t b foruw .11%; y tem f th y er pr e ly; e ng described th arran ement of electrodes in thetube 1 I is sornea whatbetter ,f-romithe standpoint of efiicient .ion-. ization and allows for agreater rangeof; grid control. That is, the tubeshown inFig, laihas the disadvantage that-the grid Isemay interfere to some-extent with the ionizing current.

An. ionizing pulse source. 20 is-connected between the cathode l3 andtheelectrodes l9, while awork circuitconnectingthe cathode 13,.to-the collector I! includesavoltage source,..shown as battery 24, and a load,- shown asthe -V0 ice -c9il 21. of a loudspeaker 29.

An audio frequency-signal source 26 is 00.1

nected between the ,control grid; l5-and theicath The signal source 26- .may comprises.

ode. l3.

on enti nal adl rec iver. a, ph nograph pick.-

up system, or the like.

W puls s f su ta le amp itudcland er tition rate are applied to theelectrodes'm from, the source 2ll, current .pulseswill flow from thecathode l3. tothe electrodesl9 and the gas in; the tube H will be ionizedas-already explained- Thein connection with the system of Fig. 1. plasma so generatedwillallow current to flow from the cathode, [3 to the collector l7 and through the voicecoil 21. Dueto the low voltage drop between the cathode l3 andthe-cob lector l1, thiscurrent can be modulated in accordance with the voltageapplied to-the control;

grid i5. Moreover, the pulse-generated plasma will not contribute noise voltages to thawork circuit curent flowing through the voice ,coil as, would be the case if a steady plasma generating, current were to flow from the cathode l3 tothe electrode 1 9.

Animp ortant application of;the principles of the invention isthe use of a simple two-elec trode gas tube, pulse-ionizedto.obtainhigh cur: rents with low voltage losses. A circuit exemplifying such an embodiment of the invention is.

shown in Fig. 3. l

The circuit of Fig. 3 comprises a rectifier system for converting alternating voltage to unidirectional voltage. In this case, a gas filled diode .30 is provided, having an electron emitter or cathode 32 andan electroncolectoror-anode connectedin a work circuit, which; includes the,

secondary. winding 48-01 a transformer-4 2 The transformer primary winding 44 is adapted :to be; connected to a suitable alternating voltage source;

(not shown) The. work -circuit-,-i s completedby nected a load, shown as a resistor 46. A pair of terminals 50 are shown at opposite ends of the capacitor 48 to designate points between which unidirectional output voltage can beobtained.

The pulse generator 36 is a so-called blocking oscillator of conventional design, energized with unidirectional voltage from any suitable source (not shown). A statement of the operation of such an oscillator will be found in Termans Radio Engineers Handbook, first edition, page 514. The generator 38 should provide output pulses of amplitude sufilcient to ionize the gas in the tube as and of repetition'rate selected in accordance with the previously mentioned factors of gas type, gas pressure etc.

The voltage applied to the transformer primary winding 4% may be the conventional sixty cycle commercial supply voltage. The peak voltage across the secondary winding All usually will be slightly less than the pulse amplitude, although this is not essential since there will be a voltage drop across the load.

The pulses supplied to the tube 31! from the source 36 will provide the necessary plasma to allow the tube 30 to conduct curent during every other half cycle of the transformer secondary voltage. The resultant rectified voltage will appear at the terminals 58 across the capacitor 68 and load 46, and with a voltage loss across the tube 30 of as little as 0.1 volt.

In Fig. 4 there is shown a system embodying a-further application of the principles of the invention, wherein a pulse-operated gas tube is used as an element in a frequency modulation detection system.

The system of Fig. 4 includes three elements commonly found in radio receivers adapted for frequency modulated signal reception. In block diagram form, these elements are shown as a radio frequency amplifier 52, a first detector 54, and an intermediate frequency amplifier 55. Frequency modulated signals received at an antenna 58 will be amplified in the R. F. amplifier 52 and converted to a lower (intermediate) frequency in the detector 54. The intermediate frequency signals from the detector 54 will be amplified in the I. F. amplifier 56, and the amplified intermediate frequency signal will be applied to a shaping circuit. This shaping circuit comprises a resistor Bil, and two rectifiers 62, 65 and bias cells 66, 68 connected in parallel in opposite polarity. The rectifiers 62, 64 will convert the intermediate frequency signal to a square wave of the same varying frequency, and of peak-to-peak amplitude determined by the resistance of the resistor 60, the conductive impedances of the rectifiers 62, E4, and the voltages of the bias cells 66, 68.

This square wave then will be applied to a differentiator circuit comprising a capacitor in and a resistor 12. By difierentiation, the square wave will be converted to one positive and one negative pulse for each cycle of the I. F. signal. These pulses will be applied to one of the cold electrodes of a gas tube 16.

The tube 16 may comprise a type 2050 tube, for example, with the anode 18 connected to the junction of the capacitor and the resistor 12.

The other cold electrode 82 (in this case, the shield electrode) and the cathode 80 of the tube 16 are connected in a work circuit which includes a voltage source 8| and the voice coil 8! of a loudspeaker 86.

As was previously pointed out, the workv circuit current in a pulse-ionized gas tube will be independent of the ionizing pulses, provided the latter are large enough and are repeated often enough. However, if the plasma is allowed to decay completely between pulses, thenthe work circuit current will drop to zero between pulses. Under these conditions, if the ionizing pulses are all of equal amplitude, then the average value of the work circuit current will be a function of the pulse repetition rate.

In the system of Fig. 4, the intermediate frequency and the dififerentiator output pulse amplitude are adjusted so that the pulsed plasma" can decay sufiiciently after each pulse to affect the work circuit current amplitude. Thus, the average value of the work circuit current becomes a function of the modulating frequency, and the latter will be reproduced as loudspeaker output.

It can be seen that the present invention provides a unique method of and apparatus for operating a gaseous electron tube in a manner that efficient control of work circuit current can be readily attained and with unusually low work circuit voltage loss at the gas tube.

What is claimed is:

1. In a method of operating a gas filled electron tube of the type havin a plurality of electrodes including a single electron emitting electrode, two of said electrodes including said emitter electrode being connected in a work circuit which includes a voltage source and a load device. the step of generating conductive plasma in said tube by applying between said emitter electrode and another of said electrodes voltage pulses of amplitude suflicient to ionize the gas in said tube.

2. Method of operating a gas filled electron tube of the type having a plurality of electrodes including a single electron emitter electrode, said method comprising the steps of generating voltage pulses of sufiicient amplitude to ionize the gas in said tube, applying said voltage pulses between two of said electrodes, one of said two electrodes being said emitter electrode, and applying between said emitter electrode and another of said electrodes a voltage of amplitude less than that required to sustain ionization.

3. Method of operating a gas filled electron tube of the type having a plurality of electrodes including a single electron emitter electrode, said method comprising the steps of generating voltage pulses of sufficient amplitude to ionize the gas in said tube, applying said voltage pulses between two of said electrodes, one of said two electrodes being said emitter electrode, and applying a separate voltage between said emitter electrode and another of said electrodes.

4. Method of operating a gas filled electron tube of the type having a plurality of electrodes including a single electron emitter electrode, said method comprising the steps of generating voltage pulses of amplitude substantially greater than that required to ionize the tube gas, applying said voltage pulses between said. emitter.

electrode and another of said electrodes, and applying a, separate voltage between said emitter electrode and another of said electrodes.

5. The method of controlling a flow of electrons from an electron emitter to an electron collector in a gas filled electron tube, said method comprising the steps of impressing voltage pulses of amplitude sufficient to ionize the tube gas between said electron emitter and another electrode in said tube, impressing a separate potential between said emitter and said collector electrodes, and. impressing a variable control potential between said electron emitter and an electrode adj acent to said emitter.

6. A gas tube system comprising a gas filled electron tube having a plurality of electrodes including a single electron emitter electrode, a source of voltage pulses of amplitude greater than that required to ionize the gas in said tube, a circuit connecting said pulse source between said emitter electrode and another of said electrodes to generate a conductive ion-electron plasma in said tube, a voltage source, and a work circuit including said last named voltage source connecting two of said electrodes including said emitter electrode to pass current between said two electrodes through said plasma.

'7. A gas tube system comprising a gas filled electron tube having an anode and a cathode, a source of voltage pulses of amplitude sufficient to ionize the gas in said tube, a circuit connecting said voltage pulse source between said anode and said cathode to ionize the gas in said tube in periodic bursts, a load device, and a circuit separate from said first named circuit connecting said anode to said cathode through said load device.

8. A system for operating a gas filled tube of the type having a plurality of electrodes including a single electron emitter electrode, said system comprising a source of voltage of amplitude less than that required to ionize the gas in said tube, a load device, a work circuit connecting two of said electrodes and including said voltage source and said load device, a source of voltage pulses of amplitude greater than that required to ionize said tube gas, and a circuit connecting said voltage pulse source between said electron emitter electrode and another of said electrodes.

9. In a system for passing space charge neutralized current between an electron emitter electrode and an electron collector electrode in a multi-electrode gas filled electron tube under conditions such that the potential between said emitter and collector electrodes is less than that required to sustain ionization of said gas, the combination with said tube of a source of voltage pulses of amplitude greater than that required to ionize said gas and of repetition rate such that the interval between said pulses is substantially less than the time required for complete elimination of ions and electrons from said gas after ionization thereof, a circuit connecting said pulse source between said emitter electrode and another of said tube electrodes, and a work circuit connecting said emitter electrode to said collector electrode.

10. In a system for passing space charge neutralized current between an electronic emitter electrode and an electron collector electrode in a multi-electrode gas filled electron tube under connected to said emitter electrode and to another of said electrodes to periodically ionize said gas at intervals substantially shorter than the time required for complete elimination of ions and electrons from said gas after ionization thereof, and a work circuit including said emitter electrode.

11. An electrical system comprising a gas filled electron tube having a plurality of electrodes including an electron emitter, a voltage pulse generator adapted to generate voltage pulses of amplitude at least suificient to ionize the gas in said tube, said generator being connected to apply said voltage pulses between said emitter electrode and another of said electrodes, and a Work circuit connecting said emitter electrode and a third one of said electrodes.

12. A gas tube system comprising a gas-filled electron tube having electrodes including a cathode and a control electrode surrounding said cathode, means connecting said cathode and another of said electrodes for periodically ionizing the gas in said tube, means to control the voltage between said control electrode and said cathode, and a work circuit connecting said cathode and another of said electrodes.

13. A gas tube system comprising a gas-filled electron tube having an anode, a control grid, a cathode and an auxiliary electrode, a source of voltage pulses of amplitude greater than that required to ionize the gas in said tube, said pulse source being connected between said cathode and said anode, a voltage source, a work circuit connecting said auxiliary electrode to said cathode through said last named voltage source, and means to control the voltage on said control electrode.

14. A gas tube system comprising a gas filled electron tube having a plurality of electrodes including a single electron emitter electrode, a voltage pulse source, circuit means connecting said emitter electrode and another of said electrodes to cause pulsating ionizing current to flow between said emitter electrode and said another electrode, said circuit means including said voltage pulse source, and a work circuit, separate from said circuit means connecting said emitter electrode and another of said electrodes, to draw current between said last named electrodes at a voltage between said last named electrodes less than that required to ionize the gas in said tube.

LOUIS MALTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,158,564 Meier May 16, 1939 2.213.551 Nelson Sent. 30. 1940

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