US2362937A

US2362937A - Electric discharge device

Info

Publication number: US2362937A
Application number: US458389A
Authority: US
Inventors: William G Shepherd
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1942-09-15
Filing date: 1942-09-15
Publication date: 1944-11-14
Anticipated expiration: 1961-11-14

Description

Nov. 14, 1944. w} G SHEPHERD 2,362,937

ELECTRIC DISCHARGE DEVICE Filed Sept. 15, 1942 FIG.

FIG. 2

- INVENTOR n. G. SHEPHERD 4 TTORNEV Patented Nov. 1944 William G. Shepherd, Summit, N'..J., assi'gnor to 1 Bell Telephone Laboratories, Incorporated, New I .York, N. Y., a corporation of New York Application September 15, 1942, Serial No.'45s,ss9

' 5 Claims.. (01. 250-275) This. invention relates toselectric discharge idevices and more particularly to gaseous discharge devices'of-the grid controlled type.

.One. object of this invention'is to-decrease the deionization. time of gaseous discharge. devices, of the grid. controlled type whereby the operating trequen-cy range thereof is increased. and their efiicacy in pulse generating systems andthe like,v for example in harmonic producers for carrier supply in telephone systems such as disclosed l2, the inner surface of which is coated with a thermionic material, and a heater filament l3 embedded in an insulating, preferably ceramic,

in my Patent. 2,314,739, granted March 23, 1943,

is enhanced.

Another object of this invention is to increase the. operating life of gaseous discharge devices of thegrid-controlled type.. H I

In one illustrative. embodimentof this invention, a gaseous. discharge device comprises a cathode, an. anodeand a control e ectrode or grid having an apertured portion between the cathode and the anode.

In accordance withone feature ofthis invention, thev cathode is an open-ended hollow memher, for example frusto-conical in form, theinner surface of whichis electron emissive and in axial alignment with the anode, and an auxiliary or deionization electrode is provided adjacent the end of the cathode furthest from the anode. The

auxiliary or deionization electrode is maintained at a fixed negative potential with respectto the cathode during operation of the device and serves to decrease the deionization time of the device and also to reduce positive ion bombardment of "the cathode emissive surface and thus to increase the operating life'of the device.

The invention and the above-noted and other features thereof will be understood more clearly and fully from the following detailed description with reference to the accompanying drawing in which:

Fig. 1 is a perspective view of an electric discharge device illustrative of one embodiment of this invention, portions of the enclosing vess'eland of the control electrode and cathode being broken away to show the internal structure more clearly;

Fig. 2 is a sectional view of the electrode structure in the device illustrated in Fig. 1.

Referring now to the drawing, the electric discharge device there illustrated comprises an enclosing vessel l0 provided with a stem 1 I and having an ionizable filling, such, for example, as argon at a pressure of the order of 0.25 millimeter of mercury.

Supported from the stem is a cathode structure comprising a frusto-conical metallic member body 14, the cathode structure being mountedgby the leading-in conductors H) for the heater filament l3' and the leading-in conductor ['6 for thecathode. The cathode is encompassed by a control electrode or grid having a cylindrical wall I1 coaxial with the cathode and adisc. end

wall. l8 having therein a central aperture l9 axially aligned with the emissive surface of the cathode and of materially smaller diameter than the adjacent end of the cathode. The control electrode or'grid is supported bya plurality of rigid metallic supports 20 embedded'in the stem Mounted opposite the end wall It in axial alignment with the cathode is adished anode'i2l,

which is supported by the leading-in conductor 22 therefor sealed in and extending throughthe end of the vessel Ill.

Adjacent the smaller end of the cathode, coaxial with the cathode and Supported bya rigid leading-in conductor 23embed'ded in the'stem l I is an auxiliaryor deionization electrode 24; which may bea. metallic disc of substantially the same diameter as'the smaller end ofv the cathode.

The initiation of the discharge between the cathode and the anode is effected by the application of asuitable potential to the control electrocle or grid ll, l8. Because of the form of the cathode emissive surface, the electrons emanating therefrom are directed toward the opening l9 and a concentrated electron flow is realized.

Inasmuch as the cathode emissive surface is out of direct line with the anode 2| through the aperture l9, it is shielded to some extent by the disc I8 from bombardment by positive ions produced in the region between the control electrode or grid and'th'e-anode. The auxiliary or deionization electrode 24, which is maintained at a negative potential with respect to the cathode during operation of the device, attracts positive ions and thus protects the cathode emissive surface from bombardment whereby deterioration or de struction in this surface by bombardment is substantially prevented and the operating life of the 1' device is increased. This protection of the oathode emissive surface by the auxiliary or deionization electrode is particularly effective when ioni-\ zation is first initiated in the device. During the period of, and immediately following initiation of ionization, the ions acquire large energies inasmuch as the voltage across the device is high and their bombarding effect upon the cathode begin until the potential of the control electrode becomes negative with respect to the cathode and this condition may not occur until some time interval after the main discharge has been interrupted so that a relatively long deionization time results. The auxiliary or deionizing electrode in devices constructed in accordance with this invention provides an additional deionizing surface which is negative with respect to the cathode so that it is effective immediately upon cessation of the main discharge for deionization purposes whereby the deionization time is reduced. It may be noted also that the deionization electrode obviates the use of large negative biases upon the control electrode to realize short deionizing time. The use of large biases upon the control electrode results in impingement of positive ions upon this electrode with large energies and this in turn may result in sputtering of material from the control electrode and consequent deterioration of the cathode and emissive surface.

Although a specific embodiment of the invention has been shown and described, it will be understood that it is but illustrative and that various modifications may be made therein without departing from the scope and spirit of this .invention as defined in the appended claims.-

What is claimed is:

1. An electric discharge device comprising an enclosing vessel having an ionizable medium therein, a hollow cathode within said vessel and having its inner surface electron emissive, an

anode opposite one end of said cathode, a con-;

trol electrode adjacent said cathode, and a deionization electrode immediately adjacent a portion of said inner surface remote from said one end of said cathode.

2. An electric discharge device comprising an enclosing vessel having an ionizable medium therein, a hollow cathode within said vessel and having a flaring inner surface coated with electron emissive material, an anode opposite the larger ,end of said surface, a control electrode adjacent said cathode, and a deionization electrode adjacent the other end of said surface.

, 3. An electric discharge device comprising an enclosing vessel having an ionizable medium therein, a hollow cathode within said vessel and having its inner surface electron emissive, an anode opposite one end of said surface, a control electrode having a portion between said anode and said one end of said surface provided with an aperture of smaller diameter than said end of said surface, and a deionization electrode adjacent a portion of said surface removed from said end.

4. An electric discharge device comprising an enclosing vessel having an ionizable medium therein, a cathode within said vessel and having a flaring inner surface coated with electron emissive material, an anode opposite the larger end of said surface, a control electrode having a portion between said anode and said end and provided with an aperture in alignment with said surface and of smaller diameter than said end, and a deionization electrode adjacent the other end of said surface.

5. A electric discharge device comprising an enclosing vessel having a gaseous filling therein, a hollow open-ended thermionic cathode within said vessel, the inner surface of said cathode being 'frusto-conical and coated with electron emissive material, an anode opposite the larger end of said surface, a control electrode including a cylindrical portion encompassing said cathode and an end portion extending between said anode and said end of said surface, said end portion having therein an aperture in alignment with said cathode and said anode and of materially smaller area than said end of said surface, and a disc-shaped deionization electrode adjacent the other end of said surface.

WILLIAM G; SHEPHERD.