US2190079A

US2190079A - Gas discharge tube

Info

Publication number: US2190079A
Application number: US171637A
Authority: US
Inventors: Wilber L Meier
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1937-10-29
Filing date: 1937-10-29
Publication date: 1940-02-13
Anticipated expiration: 1957-02-13

Description

w. 1.. MEIER GAS'DISCHARGE TUBE Filed Oct. 29, 1937 j Feb. 13,1940,

2 Sheets-Sheet 1 INVENTOR W/LBER L. MEIER ATTORNEY Feb. 13, 1940.

w. MEIER- GAS DISCHARGE TUBE Filed Oct. 29, 1937 2 Sheets-Sheet 2 -aoo INVEN TO R WILBER' L. MEIER wvw ATTRNEY Patented Feb. "13, 1940.

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Delaware Application October 29, 1937, Serial n 171,631 '7 oi 'imss olQzsoa'zasy My invention relates to electron discharge de'i vices, more particularly to grid controlled gas discharge tubes. v

In one form of gas discharge tube employing a vapor atmosphere, particularly mercury vapor, the tube is provided with a thermionic cathode and anode and acontrol electrode positioned. between the two,the gas discharge being controlled by the voltage applied to the control electrode. In this type of tube the control electrode or grid controls the starting of the discharge but normally has no effect upon stopping the discharge. The anode voltage'is usually'removedto stop the discharge and return control to theg'rid. With this conventionalarrangement the voltage applied-to the grid is'usually just sufiicientlyj nega; tive to prevent the tube from breaking down to permit a gas discharge until such time as dej-I" sired by the application of a positive voltageto 20, the grid to overcome its bias. This negative voltage must be increased as the condensed mercury temperature and vapor pressure increases to prevent an 'undesired discharge. This change in the grid breakdown voltage with change of 5 temperature and gas pressure is particularly undesirable since the constants of thecircuit elements are usually fixed and a change in the grid starting voltage interferes with the .proper operation of the tube and circuit with which it is employed. It has been customary in order to prevent this erratic operation with chan ing temperature and pressure to provide some means i for controlling the temperature of the tube so that its characteristics would remain'constant. 5 These arrangements usually result in additional apparatus which is not always simpleincreasing the cost and complicatin-g the apparatusv in which the tube is used.

It is, therefore, a principal object of myinv ention to provide a grid controlled gas. discharge tube having improved characteristics, more particularly a gas discharge tube having a grid voltage breakdown characteristic which issubstantially independent of varying condensed mer- 5 cury temperature and vapor pressure.

The novel features which I believe to be char acteristic of my invention are set forth withiparticularity in the appended claims, but the in-' vention itself will best be understood by "refer 59 once to the following description taken inconnection with the accompanying drawings in' which Figure 1 is a perspective with part of the envelope broken away of an electron discharge device made according to my inventionrFigure 2 K is a section taken along the line 2-2 ofFigure 1, jand Flgure 3 is a longitudinal section taken along the line 3-3 of Figure 2, Figure 4 is a'l circuit diagram including an electron discharge device made according to my invention, and Figure 5 is a graph showing the characteristics of 5' a conventional grid controlled gas discharge'tube and a gas discharge tube made according to my invention. Q

Referring to Figures 1. and ,2, an electron, dischargedevicemade according to my invention is provided with'the usual enveloped!) having a'v base H and press l2 from which the'electrode mount'assembly is supported. The mountjassembly may comprise an indirectly, heated cathode l3 surrounded bya solidmetal control eleca U trode 14 of cylindrical, shape coaxial uwiththe" cathode and provided with 1a longitudinally ex'g tending aperture l5 parallel to thecathode.

Mounted on. theoutside of the control electrode M and on the opposite side from said longitudi-j 20? nal slot is a semi-cylindrical anode l6, which is outfof a direct'line with the aperturewjl 5," the electrode serving also as'an. electrostatic shield and segregating the cathode from the anode and preventing the field fromthe anode extendingto .253:

supply source 2| beingthathrequired for mega- 35 tively biasing the I electrode 14 to prevent discharge until voltage from source I9 is applied. "I'heanode i6 is connected through an output 20 to onesideflof the voltage supplyrsource'zz. A switchlli may beused to remove'the anode volt- 4 ageand stop the discharge after it has oncebeen started. With a tubevrnade according tomy in,-" vention temperature and pressure changes have substantially: no effect on the biasing voltage required to prevent breakdown with the anode voltage selected. This biasingrvoltage is substantially the same underdifferent temperature and pressure conditionsso'that the circuit constants for" a*given anode voltage need not be changed 5 andthe circuit will operate satisfactorily under substantially all conditions of temperature and pressure'within the tube: I a g -While I donotwish to be limited to anyper ticular theory, I believathat the su'ccessful'op 55.

eration of a tube made according to my invention can be explained as follows:

In the conventional grid controlled gas discharge tube, as the temperature and vapor pressure increase, ionization takes place more readily so that the number of electrons necessary to cause suificient ionization for a gaseous discharge is decreased. Thus with aigiven ,negative bias sufiicient electrons may be" present in the grid-anode space at the higher temperatures and pressures to cause breakdown where this number would be insuflicientat the lower temperatures and pressures. It is, therefore, necessary to reduce the number of electrons in this space to prevent a discharge at these higher vapor temperatures and pressures. To obtain this condition it is necessary to increase the negative bias on the grid to prevent breakdown. Inv

\ by the cathode assume a distribution such that theelectron density is greatest near the cathode and less at a greater distance from, the .cathode except at the opening 15. This results the formation of a cloud of electrons on the outside of and adjacent the opening [5 in the control electrode [4. Since the cathode .isshieldedlfrom the anode field, only the electrons in this :cloud are affected by theffleld from the anode andare attracted to the anode. With proper voltages applied to the grid and anode, a sufficient number of electrons will .be attracted from-the cloud to provide the ionization necessaryof the mercury vapor within the tube to cause breakdownjof the tube. With a tube made according to my inven-j tion the grid breakdown voltage for any selected anode voltage is substantially independent of the mercury vapor temperature and pressure. It is believed that as the temperature of the mercury vapor and its pressure increase the cloud of electrons'is in effect compressed toward the cathode through the opening in the control'electrode I .4 so that the available electrons for providing the starting cathode-anode current is decreased.

However, at higher vapor temperatures and 'pres-.

sures ionization takes place "more readily so that fewer electrons will produce the ionization necessary to cause breakdown. Thus, these two effects balance each other, and by'p'roperly designing the elements of the tube'it 'ispossible to provide a tube such that the electrons available inthe electron cloud are just sufflcient at various mercury vapor temperatures and pressures'to cause breakdown of the tube at substantially the same grid voltage for a selected anode voltage. In this way the grid'breakdown voltage is made independent of the mercury vapor temperature and pressure. In the conventional type of tube, wherethe'ano'de is not completely shielded from the cathode, as the mercury vaporpressure is increased it is necessary to increase the negative bias on the grid t prevent breakdown, as described above.

A comparison of the grid voltage breakdown characteristic of a conventional grid controlled gas discharge tube and a tube made according to my invention is shown in Figure 5; The. dotted lines represent the characteristics of the conventional tube and the solid; lines a tube made accord- :-;60 C. is substantially zero. I 60 and 80..C. in a tube made according to my ining to my invention. It will be noted that with the conventional tube that with difierent tempertures of the condensed mercury vapor that the difierences in the grid breakdown voltage vary considerably and increase with an increase in anode voltage, at 500 volts the diiierence between 45 and 60 C. being substantially .8 of a volt, this difference increasing at higher anode voltages. In a tube made according to my invention the difference between the starting voltages at 45 and The curves for 45,

vention substantially overlie each other. The differencekin starting voltages is less than minus thusbe apparent in a tube made according to my invention, that the grid breakdown voltage is substantially independent of changes in condensed mercury temperatures and corresponding pressure.

tion for whichmyinvention may be employed, it

Will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that manyvariations may be made in the particularstructure used and the purpose for which it is employed without departing from the .scope of my invention as set forth in the appended claims.

What I claim as new isi 1. An electron discharge device having an envelope containing a vapor atmosphere, a thermionic cathodewithin said'envelope for emitting electrons,discharge control means surrounding andenclosing said cathode but electrically insulated therefrom and provided with a single opening through which said electrons may pass, and an anode outside of said control means and outside of adirect line with said opening but symmetrically positioned with respect to the control means and said cathode whereby the control means shields said cathode from the anode so that the field from the anode does not extend to said cathode,

2. An' electron discharge device having an envelope containing a vapor atmosphere, a straight thermionic cathode within said envelope for emitting electrons, 'a solid discharge control electrode surrounding and enclosing the cathode but electrically insulated therefrom and having a single longitudinal opening parallel to the cathode, an anode outside of said control electrode and symmetrically positioned with respect to the solid control electrode and the cathode and so disposed with respect to the opening in said conrol electrode that said control electrode shields said cathode from said anode whereby the field from the anode does not extend to the cathode.

3. An electron discharge device having an envelope containing a mercury vapor atmosphere, a straight thermionic cathode within said envelope for emitting electrons, a solid cylindrical discharge control electrode having closed ends surrounding said cathode and electrically insulated from said cathode and provided with a single longitudinal slot parallel to said cathode and an anode outside'of said control electrode and on the opposite side of said control electrode from said slot and symmetrically positioned with respect to the solid cylindrical control electrode and said cathode.

4. An electron discharge device having an envelope containing a mercury vapor atmosphere, at

thermionic cathode within said envelope for emitting electrons, a solid discharge control electrode electrically insulated from but surrounding and enclosing and coaxial with said cathode and provided with a single opening through which electrons can pass to form a cloud of electrons outside of said control electrode adjacent said opening and an anode outside of said control electrode and positioned symmetrically with respect to the solid control electrode and the cathode and so disposed that the field from said anode extends to said cloud of electrons but not to said cathode.

5. An electron discharge device having an envelope containing a vaporatmosphere, a single thermionic cathode within said envelope, a cylindrical discharge control electrode electrically insulated from and surrounding and coaxial with said cathode and provided with a longitudinal opening, insulating members closing the ends of said control electrode whereby the cathode is completely enclosed except through said opening, an anode outside of said control electrode and positioned on the other side of said control electrode from said opening and symmetrically with respect to the control electrode and the cathode.

6. An electron discharge device having an envelope containing a vapor atmosphere, a straight thermionic cathode within said envelope, and a closed by insulating members whereby the oathode is completely enclosed except through said opening, said control electrode confining the electrons from said cathode within the -space between the cathode and the control electrode except for the opening adjacent which and outside of which control electrode a cloud of electrons forms, and an anode positioned symmetrically with respect to the control electrode and the cathode and outside said control electrode and out of a direct line between the cathode and said opening whereby the field from said anode does not extend to said cathode but does reach the cloud of electrons adjacent the opening insaid control electrode.

'7. An electron discharge device having an envelope containing a vapor atmosphere, a single electron emitting cathode within said envelope, a solid metallic cylindrical electrode surrounding and enclosing said cathode but electrically insulated from said cathode and having a single longitudinal opening in the side wall thereof for controlling initiation of the discharge through said device and an anode outside of said control electrode, said metallic control electrode segregating said cathode from said anode to provide a discharge barrier between the cathode and anode except through the opening in said control electrode, said anode being positioned symmetrically with respect to the cathode and cylindrical electrode surrounding the cathode and disposed so that the field from said anode cannot extend L. MEIER.