US2948825A - Electric-discharge device - Google Patents

Description

D. F. RILEY ETAL ELECTRIC-DISCHARGE DEVICE Filed July 23, 1958 Aug. 9, 1960 2,948,825 Erasmo-DISCHARGE DEVICE Daniel F. Riley, Braintree, lSeymour Goldberg, Lexington, and Kenneth J. Germeshausen, Newton Centre, Mass., assignors to Edgerton, Germeshausen and Grier, Inc., Boston, Mass., a corporation of Massachusetts Filed July 23, 1958, Ser. No. 750,488

`4 Claims. :(Cl. 313-193) The present invention relates to 4electric-discharge devices and, more particularly, to gaseous-discharge devices of the thyratron or rectifier type, and the like.

Electric-discharge devices, of the above-mentioned character, are frequently used in pulsing circuits, such as, for example, pulse modulators and the like of the type described in United States Letters Patent Nos. 2,518,879, issued August 15, 1950, and 2,722,629, lissued November l, 1955, to the applicant, Kenneth l. Germeshausen, herein. One of the ,problems Vinherent in such use, is that of so-called inverse voltage effects; wherein, 'after `a pulse of current `has been produced in the discharge device, it is desired that the device promptlyY cease conducting Vand .remain insensitive to breakdown in `response to Vinversely applied voltages resulting from oscillations in the pulsing circuit, or otherrcause. Particular rceramic envelope discharge tubes that may lbe subject `to `such diiculty are described, for example, in application, Serial No. 599,728, now Patent No.2 j84'2'6'99 filed by. two of the applicants herein, Seymour Goldberg and the said Kenneth L .Germeshausem on July 24 ,1.956, for Gaseous Seal and Method. Y

An object of the lpresent invention, accordingly, is to providea new and improved electric-discharge device that shall not ybe subject to the Vabeve-.rne'nti'oned difficulties and thatshall, to the contrary, be=enabled to hold off fa'r greater inverse voltage 'effect-s than :hasfhereto'farejbeen feasible.

A further object is to provide a new and improved gaseous-discharge device of more general character.

`Other and further objects will be explained hereinafter -and will be more particularly pointed out in the appended claims. In summary, the invention, from perhaps its broadest point of View, resides in the provision of an electric-discharge device having a pair of cooperative electrodes defining a discharge region therebetween, and disposed in an insulating envelope, but spaced from the inner wall of the envelope. A conductive path is disposed external to the discharge region in the space between the said inner wall and the electrodes, preferably along the inner wall. Preferred details are hereinafter set forth.

The invention will now be described in connection with the accompanying drawing,

Fig. 1 of which is a longitudinal section of a discharge tube embodying the invention in preferred form; and

Fig. 2 is a fragmentary perspective taken along the line 2-2 of Fig. l, looking in the direction of the arrows and showing details of construction.

For purposes of illustration, a thyratron-type gaseousdischarge tube is illustrated in the drawing, as of the hydrogen-filled type, comprising a substantially cylindrical ceramic envelope 1 containing a cup-shaped anode-electrode 3, having a substantially planar anode surface 3 and outwardly extending heat-conducting and electrodeconnection flanges 3, solder-sealed at 2 between the upper edge of the ceramic envelope 1 and the bottom edge of a cylindrical ceramic sealing ring 1 that assists in States Patent O ICC ,2 Y giving mechanical strength Vto the seal. The seal Zmay be of the `type described 'in the said vcopending application of vGoldberg and' Germeshausen. vCooperating withthe anode electrode surface 3 is a closely-'spaced substantially parallel, preferably 'apertured, planar lelectrode surface 5' of an inverted cup-shaped controler .grid electrode 5, also provided with outwardly extending flanges "5,

similarly sealed at 2 between Vthe bottorn'edge of the fen-V in said copending application, in order to `provide longv arc-discharge paths.

vWithin the cup-'shaped control electrode :5 may -Vbe disposed a cathode electrode '7, illustrated 'as Ap'f an inverted cup-shape having similar outwardly extending fanges 7 sealed at 2 between 'the ceramic ring 1" 'and a ceramic base 9. y'l`l1ec'atlf-iode cup y7 may fcontain, at i-t's upper open end, a plurality of vane-type electrodes "f ofthe type described in -a further copendingapplication, Serial No. 580,551,'led April25, 1956, by Ithe said applicants Germeshausen and 'Goldberg for ,Electric-Discharge De-A vice and Cathode. A gas reservoir 11, ofthe type described, for example, lin application, 'Serial No. 714,086 filed February 150,- 19513, by the said applicant Seymour Goldberg, et al., for Gaseous Reservoir jand `Method,may be vdisposed within the cathode cup`7, `and may be heated by current 'passed along conductor-supports 11 and 11". Above "the upper vsurface of the cathode vanes 7 may "dispose 1a baille 13 having a central aperture 113. A :similar `.baille I5, having apertures 15" fsta'ggered so as 'to `be displaced from the apertures 4 of thesgrid-electrodefsurface 5 mayalsobeprovided. y. In operation, `dueto lthe presence of ionization in the. tube and the unavoidable existence of minutey :asymmetries, caused either -by -small -loose particles on the inner ceramic walllgordimens'ional inaccuracies, local regions :of the inner ceramic wall, such as 'the regioni between tthe fdischa-rge region defined by vthe anode surface 3 yand the control electrode surface 5', may be bombarded to a greater extent with ions or electrons (depending upon the asymmetries and the polarity of the anode potential). These local regions will thus be caused because of their non-conductive properties, to charge to considerable voltages. Since such local regions, charged to high voltage, are adjacent to other regions of the ceramic wall 1 which are substantially uncharged, severe electric-field gradients are set up. In tubes of this type, the potential at the region P on the inside wall of the ceramic envelope 1, mid-way between the anode surface 3 Aand the control grid surface 5 may be approximately l5 kilovolts. After the tube has been triggered, and inverse voltage is applied by oscillation in the circuit, or otherwise, between the anode 3 and control electrode 5, the potential at the region P has not had time to decrease or bleed off. When the inverse voltage, which may be of the order of 10 kilovolts, becomes added to the 15- kilovolt potential upon the charged region P, a resultant potential of 25 kilovolts may be produced. While the tube might hold off inverse voltages of the order of Vl0 kilovolts, the 25 kilovolts will cause breakdown in the in- Current will thus continue to flow withverse direction. out permitting the tube to recover before the next positive pulse is applied to trigger the same.

In accordance with the present invention, these prob- 3 inner wall 1 and the side edges or walls of the electrodes 3 and 5. The band C is preferably provided as a coating or layer upon the inner wall 1 itself, in the region P, and it has been found to have the effect of preventing the above-mentioned accumulative charge upon the wallsV o'f the envelope 1 in the region P. 'Such charge, to the contrary, will occur above the anode surface 3' or below the control electrode surface 5', but not opposite the Vdischarge region therebetween. To obtain best results, it has been found that the band or conductive path C is preferably of length at least equal to the length of the discharge region between the electrode surfaces 3' and 5', but preferably extending somewhat beyond, both thereabove and thercbelow, along adjacent portions of lthe side walls of the cup-shaped electrodes 3 and 5, as shown.

This construction provides for a much higher breakdown voltage in the inverse direction. Considered from -a circuit viewpoint, the RC time constant inherent in the charged-wall region P of the ceramic envelope 1 has been reduced by several orders of magnitude, permitting the potential at the point P to decrease rapidly. Even if the region P is bombarded with an excess number of ions or electrons, intense local fields can not develop since the bombarding charges are readily conducted away by the conducting path C. Instead, the potential of the entire conducting path C Will change, with no local intense fields in the actual region near the anode surface 3.

. herent simplicity. Various predetermined potentials may Since the conductive path C has greater electrostatic capacity than a local region of the ceramic Walls, variations in potential of the conductive path C over a given time will be less than that which would occur at a corresponding region of the ceramic inner wall itself.

As an illustration, hydrogen thyratrons of this type have been fabricated with two successive conductive-layer coatings C painted on the region P and fired. The coating material was liquid-bright platinum consisting of 50% platinum and 50% gold. The coating was in the form of a band 3s-inch high on the inside surface, centered in the region P between the anode surface 3' and the control electrode surface 5. The tubes were tested in a pulse modulator circuit in which prior-art thyratrons, not incorporating the conductive path C, would hold off inverse voltages up to 14 kilovolts. The tube of the present invention with the conductive path C, on the other hand, was found to hold off inverse voltage spikes of at least also be applied to the conductive path C, if desired.

Further modications will occur to those skilled in the art, and all such are considered to fall within the spirit and the scope of the invention, as defined in the appended claims.

What is claimed is:

l. An electric-discharge device having, in combination, electrode surfaces defining a discharge region therebetween and disposed within an insulating envelope with the edges of the electrode surfaces spaced from the inner wall of the envelope, and a conductor electrically isolated from the electrode surfaces and embracing the discharge region in the space between said inner wall and said edges of the electrode surfaces, said conductor extending at least the length of the discharge region between said electrode surfaces.

2. The discharge device of claim 1, said electrode surfaces including cathode, anode, and grid electrode surfaces, said conductor surrounding said discharge region and extending at least `the length of the discharge region between said anode and said grid electrode surfaces.

3. The discharge device of claim 1, one of said electrode surfaces being a substantially planar surface of a rst cup-shaped electrode, the other of said electrode surfaces being a substantially planar surface of a second inverted cup-shaped electrode, said electrode surfaces being substantially parallel.

4. The discharge device of claim 1, said conductor being mounted on the inner wall of said envelope.

References Cited in the le of this patent UNITED STATES PATENTS 2,492,666 Sloan Dec. 27, 1949 2,654,850 Smith Oct. 6, 1953 2,739,262 Watrous Mar. 20, 1956` 2,842,699 Germeshausen et al July 8, 1958

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