US2072979A - Tube and system for electron discharges - Google Patents

Description

March 9, 1937. H. G. CORDES 2,072,979

TUBE AND SYSTEM FOR ELECTRON DISCHARGES Filed April 50, 1930 2 Sheets-Sheet l INVENTOR March 9, 1937.

H. G. CORDES Filed April :50, 1930 2 Sheets-Sheet 2 P Lwl 6 ww-$--l**- INVENTOR Patented Mar. 9, 1937 PATENT OFFICE TUBE AND SYSTEM FOR ELECTRON DISOHARGES Henry G. Cordes, Palo Alto, Calif.; Bertha L.

Cordes, executrix of said Henry G. Cordes, deceased, assignor to Bertha L. Cordes, widow Application April 30, 1930, Serial No. 448,613

16 Claims.

This invention relates to a container of condensable gas in which electrodes are provided to pass intermittent unidirectional electron discharges to an anode located in a low pressure part of the container. It pertains particularly to a container of mercury vapor having an electron-emitting cathode, such as a pool of mercury or an incandescent filament in vapor, in addition to the anode, and to a system in which it is used.

One object is to provide the container with an anode chamber in which the required high rareiaction is simply, efiicaciously and efliciently maintained. Another object is to initiate an electron discharge thru the highly rarefied part of the discharge path, and also to control the electron fiow when it is desired to produce high frequency discharges. A further object is to provide a system, comprising suitable sources of current and potential, to utilize the highly rarefied anode space.

These objects are attained by providing the container with a novel condensing chamber adjacent to the discharge path near the anode chamber, by varying the gas pressure in the anode chamber, by reducing the arc-initiating voltage with suitably disposed conductors, by introducing a periodically variable electrostatic field into the discharge path, and by providing other features of the system which will be pointed out in the following detailed description of the invention.

The term, condensing chamber, is used herein to refer to a space in a tube provided primarily for condensing vapor, hence it contains neither an electrode nor a discharge path which heat the chamber and thereby tend to prevent condensation. The word, cathode, refers to a conductor capable of emitting electrons and anode refers to a conductor in the tube capable of collecting and absorbing electrons.

I vary the breakdown value of the discharge path by placing a charged surface adjacent to the path so as to suitably influence its space charge independently of, or in addition to, that produced by its terminal electrodes. Decreasing the negativity of the space charge decreases the potential required to break down the path and increasing it has the reverse effect. Any means for collecting electrons or positive ions from the path will influence its breakdown value for any given electrical state of the electrodes at the terminals of the path.

The drawings, forming part of this specification, illustrate the novel features of the invention. Figure 1 shows a tube in a system for initiating, sustaining and controlling electron discharge. Figure 2 shows a modified form of the anode chamber. condensing chamber located adjacent to the discharge path of a rectifier tube.

In Figure 1 the Pyrex glass tube 2 consists principally of a mercury cathode 3, a main condensing chamber 4, an anode arm 5 terminating in a nozzle 5, an auxiliary condensing chamber I having a mercury trap 8 at its lower end, av condensed mercury return tube 9, an anode chamber I0, and a float chamber H. Adjacent to the cathode 3 is an arc-starting arrangement which includes mercury |2, glass float l3 in chamber M, an iron solenoid-core I4 in the upper part of l3, a leading-in conductor [5, and a solenoid winding IS. The anode chamber l0 contains an electron-supply anode 20, a control conductor 2|, and a diverted-electron-fiow anode 22. The control conductor 2| is water-cooled by water passing thru tubing to, and from, a jacket 25 sur- I rounding the metallic tube 2|. The metal- toglass seals 23 and 24 are also water cooled. The source of water flow is insulated from anode 22 and from anode 20 which is grounded.

The anode arm 5 is provided with conducting bands 30 and 3|. The band 3|] consists of a high resistance metallic film on the glass of nozzle 5 and is connected conductively to the band 3| by the leading-in wire 32.

The circuit for producing a starting are between mercury I2 and mercury cathode 3 includes a switch 35, a battery 35 and a current limiting resistance 31.

The circuit for starting and sustaining the ionizing are between anode 20 and cathode 3 comprises a direct current generator 40, an ironcore inductance 4|, an air-core inductance 42. and a resistance 43 in series between anode 20 and cathode 3. A multi-contact oil switch 44 is placed in parallel with the discharge path between 20 and 3 and part of resistance 43. The anode 20 is connected to bands 30 and 3| thru condenser 45. The current supply conductor 45 to anode 20 is insulated by quartz tube 41 inside the anode chamber.

The diverted-flow-anode supply circuit comprises a direct current generator 50, an ironcore inductance 5|, an air-core inductance 52, and a resistance 53 connected in series between anodes 20 and 22. Condenser 54 in series with inductance 55 are placed in parallel with the dis- Figure 3 shows an auxiliary charge path between anodes 20' and 22. An energy absorbing circuit 56 is coupled to inductance 55.

series between anode 20 and control conductor 2|. The primary of transformer 60 is connected to a source 64 of high frequency current which has a lower frequency than the natural frequency of a simple circuit consisting of condenser 54 and inductance 55 in series.

The auxiliary condensing chamber 1 is placed in a liquid bath comprising the container 10, liquid ll, coils l2 and 13 of tubing immersed in the liquid, a source 14 of heat from which hot fluid can be passed thru coil 12, and a source 15 of cold from which a cold fluid can be passed thru coil 13. Water or a refrigerant gas provides a suitable cold fluid.

A heat-insulating cap is provided to flt over the main condensing chamber. The vapor pressure in arm 5 may be varied by raising or lowering this cap.

The operation of the tube and associated equipment consists in starting an are between mercury l2 and cathode 3, initiating and sustaining electron discharge from cathode 3 to anode 20, and producing intermittent electron discharges in the anode chamber between anodes 20 and 22. A more detailed description of the function and operation of each part of the tube and of each exterior unit of the system follows.

A starting arc is formed between mercury l2 and cathode mercury 3 by energizing winding ii to pull down the float l3 which displaces mercury l2 thereby making contact between l2 and 3 so that current flows from the battery 36 thru resistance 31 and switch 35; then I6 is de-energized, the float l3 rises, and mercury l2 breaks contact with mercury 3 thereby forming a cathode spot on mercury 3.

An arc is next initiated between electron supply anode 20' and cathode 3 by first heating coil 12 to increase the vapor pressure in the auxiliary condensing chamber 1; then the direct current generator is loaded by closing switch 44 to pass a relatively large current thru iron-core inductance 4|; and, finally the current is broken so that a high rate of change of current in 4| produces a sufllciently high positive potential on anode 20 with respect to cathode 3 to initiate a discharge. The potential required to initiate a discharge is reduced by the relatively high vapor pressure in chamber 1 and by the decreased negativity of the space charge produced by the bands 30 and3l. After a sustained discharge of constant value has been established between 20 and 3, the switch 35 is opened, heat supply to coil 12 is stopped, and cooling fluid is supplied to coil 13 to cool chamber I to the desired temperature. A relatively small amount of vapor is condensed in chamber 1 compared with the amount condensed in chamber 4; this greatly reduces the amount of cooling medium required to keep I at the proper temperature. The amount of cooling medium required is further reduced by the mercury condensed in 1 being returned to the cathode thru tube 9 instead. of thru arm 5 where re-evaporation would take place. The diffusion pump action of the vapor flowing from nozzle 6 to chamber 1 reduces the pressure of non-condensable gas which may exist in the anode chamber. In the discharge path a high vapor pressure exists between the nozzle and the cathode compared with the pressure between the nozzle and the anode;tubes having this feature have been used in the past but the pressure used in both the high and low pressure parts of the path was much greater and no special means, such as conductor 30, heat source 14, or switch 44, were required to initiate electron flow to anode 20. One of these novel features may be provided to operate the tube described by Szilard in Patent 1,697,210 in order to reduce the required operating voltage or to make the tube operate at lower gas pressures surrounding the grid and anode. The auxiliary condensing chamber 1 which is adjacent to the discharge path is heated comparatively little by heat radiated by the discharge. The lowest temperature of any part of chamber 1 largely determines the vapor pressure in the anode chamber In so that the pressure surrounding the anodes 20' and 22 can be varied by varying the temperature of chamber 1. As the temperature of 1 decreases below a certain value, the arc-drop thru the low pressure part of the discharge path increases due to decreased vapor pressure until electron-supply anode 20 becomes incandescent and constitutes a source of secondary electron emission; as the arc-drop increases the tendency for the arc to become extinguished increases; this tendency can be overcome, to a certain extent, by increasing the potential of source 40 and also by re-- ducing the capacitance between anode 20 and the cathode to a minimum.

The anode 20 may be placed in anode arm 5 or in the main chamber 4 to reduce the voltage drop between 20 and the cathode but the potential required on anode 22 to divert electron flow will thereby beincreased;

The diverted-flow anode supply circuit supplies the energy for the high frequency current output of the system. From generator 50 a direct current flows thru choke coils 5| and 52 to either the anode 22 or to condenser 54 to produce linear-sinoidal oscillations in the discharge circuit comprising 54 and 55. The energy of the oscillations is absorbed by an antenna, an absorbing circuit 56, or other energy consuming arrangement. These oscillations are produced by making the gas-space between anodes 20 and 22 alternately conducting and non-conducting at a high frequency. When the space is conducting, electrons flowing from the cathode to anode 20 are diverted to anode 22; any secondary electrons emitted by 20 may also flow to 22. When the space is non-conducting, all electrons flowing from the cathode are collected by anode 20 and no electrons flow to anode 22. When the control conductor 2i is connected by switch 62 to anode 20, the conductor becomes charged -sufliciently inegative with respect to anode 22 to prevent initiation of electron flow to anode 22 due to -the increase of negativity of the space discharge produced by the negative bias. By superposing an alternating potential on the negative bias the potential of control conductor 2| becomes sufl'iciently positive during a high frequency cycle to instantaneously overcome, or neutralize, the negative effect to permit intiation of electron flow to 22. It is thus seen that the frequency of electron discharges to diverted-flow anode 22 is determined by the frequency of the constant amplitude current source 64. The leakage resistance 6! allows the positive ion current, that is, the current due to the positive ions collected by 2|, to leak to anode 20 which is grounded. The proper value of the resistance depends on the degree of rarefaction inside of 2i, on the potential impressed on conductor 2! by transformer 60, on

the value of the bias voltage of 20, and on the senseand value of the additional bias of battery 63. k

The control conductor 2| has the novel feature of having a single opening as distinguished from a grid having numerous mesh oT'bpenlngs thru which the electrons may flow; this construction assures that electron fiow' takes place always thru the same opening instead of fortuitously thru alternative openings. An-

other characteristic feature isthe comparatively large ratio of length to effective diameter of the discharge path thru the conductor; by constrioting the path its length can be reduced and the tendency to intermittent flow is increased. The collection of positive ions by conductor 2| during a greater part of a cycle causes it to become heated which may result in undesirable secondary emission; this is prevented by watercooling the conductor and by keeping the vapor pressure low by means of the auxiliary condensing chamber 1. Cooling the conductor 2| tends to make it immune to undesirable efiects of positive ion bombardment while reducing the gas pressure adjacent the conductor by chamber 1 reduces the number of positive ions present. The electrostatic field, inside of conductor 2| upon which the breakdown value of the space depends, increases in effectiveness as the gas pressure decreases. The total electron flow from the cathode remains constant while the electron flow to anode 20 is periodically diverted to anode 22 by periodic variations of the electrostatic field. The magnetic field in conductor 2| is maintained constant by passing the sum of the currents to anodes 20. 'and 22 thru 2|. The variations of magnetic field produced by variations of electron fiow to I anode 22 are neutralized by variations of magnetic field produced by variable current fiowing thru conductor 46.

To produce high frequency intermittent flow of electrons to anode 22 in the presence of a constant flow of electrons from the cathode to anode 20: Close switch 62, start generator 50 and then start generator 60. The voltage required of generator 50 depends on the rarefaction, eifective diameter, and length of the discharge path thru 2|; it increases with decrease of diameter and with increase of length and rarefaction.

It is thus seen that electron-supp y anode 20 functions as a virtual main cathode but does not become disintegrated in which respect it differs from an electron-emitting electrode. Among-the advantages of a virtual over an actual cathode are avoidance of disintegration or consumption of electrode material due to cathode sputtering and the consequent ability to maintain a relatively low and uniform gas pressure adjacent to the electrode. Other advantages such as control of initial velocity of electrons, constant rate and rapid de-ionization, etc., are obvious to those skilled in the art.

Figure 2 shows a modified arrangement of the anode chamber ID with respect to the electrodes and especially the control electrode. The chamber l0 contains an electron supply anode 20', a positive ion collecting grid 26, control grids 22|, and diverted-flow anode 22. A number of grids are connected internally or'externally (as shown) in parallel thru resistances 21. A battery 28 is provided to charge grid 26 negative with respect to anode 20 and the ground.

The electrical connection to control conductor 22| is similar to the connection to control conductor 2| of Fig. 1. Two types of electron-flow to anode 20 being diverted to anode 22.

control can be produced by conductor 22|. I will refer to these types as voltage control and currespect to anode 20 at which electron flow to 22 begins. Current control is the type which takes place in three-electrode thermionic tubes; the control conductor determines the current flow to anode 22 which depends on the voltage-drop thru the tube while current is flowing. Current control in gas tubes is generally limited to relatively low voltages. The properties of such tubes have been described by Liibcke in the Zeitschrift fiir technische Physik, Nr. 11 of 1927 and also in the Zeitschrift fiir Hochfrequenztechnik of July, 1928.

Assume that electron-flow to electron-supply anode 20. is taking place and that a somewhat smaller electron-flow passes to anode 22; under this condition a high frequency voltage of proper value impressed on current control conductor 22| will vary the electron-flow to anode 22 periodically at the same frequency and thereby transmit energy to circuit 56. The grid 26 may be added to collect positive ions before they reach the lower grid of 22|. The anode 20 is made of two parallel perforated plates having. staggered perforations to reduce the velocityof electrons at 20 which pass to anode 22. The control grid 22| is made of screen having a suitable size of wire and mesh so that the electron discharge does not-concentrate and flow thru a single opening or mesh.

. To produce voltage control grid 26 is charged sufficiently negative to prevent any electron-flow A sufficiently high positive potential on grids 22| will neutralize the increased negativity of space discharge produced-by grid 26 so that by making 22| periodically positive electron discharge will be diverted to anode 22 at the same frequency.

Figure 3 shows the upper part of an anode arm 305 of a multi-anode rectifier tube. The arm is provided with an auxiliary condensing chamber 301 whichconstitutes the novel feature of this' construction. The temperature of the part of chamber 301 most remote from the discharge path determines, to a large extent, the vapor pressure surrounding anode 320 in the anode chamber |0 tact with the discharge path.

In a rectifier tube the mercury cathode emits electrons continually either by overlapping of phases or by a keep-alive current. It is known that in the presence of this continual emission a very high positive potential must be impressed on the anode with respect to the cathode to initiate an electron discharge when a part of the discharge path is highly rarefied. This phenomenon is called fading. The part of the path from the anode to the nozzle 306 is highly rarefied so that means must generally be provided to reduce the voltage required to initiate electron flow at the beginning of each half cycle or transient flow period. For this purpose I provide a number of piloting electrodes- 34 which are charged thru condensers 33!. This arrangement functions similarly to the band 3| of Fig. 1 to produce longitudinal piloting in the manner that I have described in my copending v application, Serial Number 228,233; each piloting electrode 3 primes a discharge from the electrode 31 nearest above it.

The improvement illustrated by Fig. 3 has a number of advantages when compared with the usual arrangement of immersing the whole tube in oil. I have found that it is not desirable to cool the mercury of the cathode nor the cathode end of the discharge path in order to increase the voltage which can be rectified but that it is necessary, however, to reduce the vapor density near the anode. When a tube is immersed in oil all of the tube is cooled; the cathode which preferably should remain hot transmits heat to the oil which should remain cold. A continuous hot path is provided by the discharge from the cathode to the anode so that the vapor pressure surrounding the anode is determined by the temperature of the coolest part of the path and this temperature is relatively high due to the discharge. Compared with oil cooling a much smaller amount of cooling medium applied to chamber 301 will more effectively and eiiiciently produce the .de-

sired low density of vapor adjacent to the anode.

I have set forth the novel features of my invention in the following claims.

I claim: 1. A vacuum tube comprising a cathode having vapor adjacent thereto, at least two anodes, a vapor condensing surface between the cathode and one of said anodes arranged to be heated only by vapor condensing thereon, and a control surface capable of controlling electron flow to at least one of said anodes combined with a source of unidirectional current connected to divert electron flow from one to the other of said anodes.

2. The combination of a mercury vapor tube comprising two anodes, means for maintaining the first of said anodes and the ground at the same potential, and means for maintaining the second of said anodes at an average positive potential with respect to the first of said anodes.

3. A vacuum tube comprising a discharge path having adjacent thereto a conducting surface in combination with means for varying, at high frequency, the electron-flow thru said path, and means for neutralizing the variation of magnetic field in said surface produced by said varying flow.

4. In a system for electron discharge a vacuum tube comprising an anode, a discharge path terminating at said anode, and a cooled control conductor capable of increasing the breakdown value of the space charge of said path, and electrical energy supply for charging said conductor with a potential varying at a. radio frequency and having an average negative value with respect to any positive ions adjacent thereto.

5. In a vacuum tube for electron discharge a condensing chamber, an anode, and a discharge path terminating at said anode, containing vapor, and divided into high and low pressure parts by said chamber combined with a composite surface comprising a plurality of elemental surfaces disposed in said high and low pressure parts, each capable .of decreasing the breakdown value of the space charge in said path.

6. In a system for electron discharge a vacuum tube comprising a cathode having vapor adjacent thereto, two anodes, a discharge path between said electrodes, and a condensing chamber, a source of potential between the cathode and one of said anodes, and a second source of potential arranged to maintain an average difference of potential between said anodes.

7. A mercury vapor tube having at least two anodes combined with a low impedance to high frequency current disposed between one of said anodes and the ground.

8. In a system for electron discharge a vacuum tube comprising two anodes combined with at least two conductors in parallel between said anodes; one of said conductors comprising capacitance in series and the other of said conductors comprising the main source of unidirectional current energy supply to said tube.

9. In a system for electron discharge a vacuum tube comprising an anode and a discharge path terminating at said anode and containing vapor, means for starting and maintaining a continuous electron flow thru said path, and cooling means for decreasing the pressure of the vapor, after said flow has been started, to the extent that the voltage drop thru the vapor adjacent the anode is thereby increased to a sustained fixed high value.

10. In a system for electron discharge a vacuum tube containing vapor at a pressure of less than twenty microns of mercury and an anode surface adjacent thereto a continuous electron flow to said surface, and means including a source of electrical energy for making said surface become a virtual source of electrons.

11. A vacuum tube comprising a cathode having vapor adjacent thereto, an anode charged to a positive average potential with respect to the cathode, a second anode, a discharge path ter-- zninating at said second anode, and a cooled sur- ,a source of potential arranged to charge said second anode to a positive average potential with respect to the first-mentioned anode. 12. A vacuum tube comprising an electronsupply anode capable of suplying electrons by di-.

version, a diverted-flow anode, and a plurality of control surfaces separated by impedance and capable of influencing electron flow to said diverted-flow anode combined with a source of varying potential connected to said surfaces.

13. In a system for electron discharge a vacuum tube comprising two electrodes adjacent to gas capable of becoming a source of positive ions and a control surface therebetween arranged to avoid undesirable secondary electron emission therefrom caused by positive ion bombardment, an inductance and a capacitance in series connected between said electrodes, and a source of potential containing two components connected to said surface; the first of said components being constant and the second being alternating at a frequency less than the natural frequency of said inductance and capacitance.

14. The method of operating a system for electron discharge which comprises passing a dual current thru rarefied gas by simultaneously producing electron flow to two surfaces and superposing an oscillatory current on the dual cur.- rent during at least part of a cycle of the oscillatory current by producing a periodic flow of displacement current with continuous current energy.

15. The method of operating a vacuum tube provided with a discharge path terminating 'at an anode and containing vapor which comprises producing a vapor pressure in at least part of the path, in the presence of continuous electron flow to the anode, of less than one half of its saturation value by diverting the flow of vapor from the path at a plurality of points along the path to surfaces having suitably low temperatures.

16. A vacuum tube comprising a cathode having vapor adjacent thereto, an anode surface having a continuous flow of electrons impinging thereon, cooling means including a vapor-condensing surface arranged to reduce vapor pressure adjacent said anodesurface to the extent that the minimum potential drop between said electrodes is at least doubled, anda second anode surface charged to a. positive average potential with respect to the first-named surface.

HENRY G. COR-DES.

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