US2508529A - Gaseous electronic discharge device - Google Patents

Description

May 23, 1950 P. R. MENZEL ETAL GASEOUS ELECTRONIC DISCHARGE DEVICE 3 Sheets-Sheet 1 Filed March 6, 1948 hams/v25; INVENTORS KLRONCI R. L. VANC BY 4 A T IORNEV May 23, 1950 P. R. MENZEL ETAL GASEOUS ELECTRONIC DISCHARGE DEVICE 5 Sheets-Sheet 2 Filed March 6. 1948 P. R. MENZEL uvvgurons m. RO/VC/ R. L. VANCE By ,.%M

A r TORNEV May 23, 1950 P. MENZEL ET AL GASEOUS ELECTRONIC DISCHARGE DEVICE 3 Sheets-Sheet 3 Filed March 6, 1948 m mwwmw mivw l v l n FIG. 9

L g MN Mw RA RV. m M w m R. L. VANCE ATTORNEY 3 configuration of the control path in the trigger element to reduce the internal impedance to the flow of electrons between any point on the oathode area to the anode surface. This is accomplished by forming a plurality of equally spaced crossing slots in the fixed baflie disc element which forms a "uniform bifurcated multiarmed or star-shaped passageway for the projection of electrons along the discharge path between all portions of the cathode and anode areas. The

restricted slots permit control of the electron discharge since the control potential developed in the field of the slots assures a positive blocking action on the electron flow yet permits direct flow of electrons when the grid is biased less negatively to allow the electrons to flow to the anode over a, low impedance path between any point on the cathode area to any point on the anode area.

A further feature of the invention relates to the mounting assembly of the cathode to protect the active coating thereon from poisoning and deactivation. The highly emissive hot filament ribbon is enclosed ina heat conserving casing which is so constructed that copious electron flow is projected toward the anode but spurious back emission or bombarding electrons from the anode are substantially deflected before reaching the active coating on the filament. This is accomplished by providing a double-walled cage around the cathode, the cage havinga baffle cover which permits egress of electrons from the filament through [a restricted annular orifice. However, electrons ment prevents deactivationof the coating and achieves longer operating life forthe device. These and other advantages of the invention will be more clearly setforth inthe following detailed description of a particular embodiment of the invention shown in the accompanying drawings. In the drawings:

Fig. 1 is a perspective view showing the external appearance of a device made in accordance with this invention and embodying the features set forth above; n r v v Fig. 2 is a view in elevation showing the crosssection of the device of Fig. 1 and illustrating the detailed assembly of the components of the device;

Fig. 3 is a perspective view of portions of the "main sections of the. device; shown in exploded fashion to illustrate the details of the construction;

. Fig. 4 illustratesa section view in elevation of the detailed assembly of the components of the cathode construction-taken onthe line 4-4 of Fig. 2, showing the protective casing and the mounting of the filament therein;

Fig. 5 is a perspective vie'w'in exploded fashion .showing the array of parts entering into the assembly of the cathode mounting as employed in the device of this invention; v

Fig. 6 is a viewiri elevation, partly in crossiii) 4 section, of a modified construction of the cathode portion of the device of Fig. 2;

Fig. '7 is an enlarged plan view of the cathode casing with the cover removed and showing the configuration of the cathode ribbon;

Fig. 8 shows the cathode unit casing in elevation view, in section taken on the line 8-8 of Fig. 7, to illustrate the detail assembly of the elements therein, and

Fig. 9 is a perspective view of the cover and shielding assembly of the cathode casing of Fig. 6, with a portion broken away to show the detail construction.

Referring to the drawings, and particularly to Figs. 1 to 5,'inclusive, a specific constructionofone form of the invention is embodied in an allmetal thyratron or grid-controlled electronic discharge device of the vapor conduction type which is sturdily constructedto provide a highly efficient device having a long operating life at high power ratings.

The device, as developed, is composed of three elemental components, namely, a cathode section. an anode section, and a barrier control element. which are integrated in precise relation to facilitate the fabrication of the device on a mass pro duction basis and to achieve dynamic characteristics which are uniform and efliciency which is stable over long operating periods.

-The cathode section of the metal casing of the device is composed of a cylindrical steel shell Ill open at one end i i and having an inturned flange l2 at the other end, asshown in Fig. 3. A disc closure plate I3, of similar material, is welded to the exterior of the flange to form a deep cup receptacle for the mountingof the cathode therein. The closure is provided with a pair of large apertures in parallel relation across a main diameter of the disc and a smaller aperture offset from the center of the larger apertures, to provide the coupling of tubular extensions to the bottom of the cathode section, as will be described hereinafter. In addition, a pair of threaded studs 14 are brazed to the plate I 3 in symmetrical relation onthe opposite side of the large apertures. A deep-drawnsteel well I5 is brazed or welded to the plate [3' and extends downwardly from the offset smaller aperture therein while a pair of nickel-iron-cobalt alloy sleeves l6 and I1, preferably of a metal such as Kovar, are welded and brazed to the inner surface of the plate through the large apertures by means of flange portions 18 on the contacting rimsof the sleeves, as shown in Fig. 2.

The outer ends of the sleeves l6 and I! are hermetically sealed to short sections of hard glass tubing l9, preferably of boro-silicate glass, which ,has the same thermal expansion characteristics a tubular extension or tubulation 23 for connection to a pumping station for evacuating the device and forms a seal-off after the desired filling of mercury is injected into the device.

The tubulation 23 is preferably formed of Kovar alloy to readily seal the device to a glass header on the pumping station, although any other metal may be used, suchras steel, copper or brass if the facilities 'for' connection'to the pumping 5 station header are suitable for attaining a tight Joint at the 'jun'ction'of the'tubulation and header. The-device is-inverted when connected 'tothe pumping station so that the'tubulation 23 is at the top; In this position, the desired amount of mercury-- may be'injectedinto thedevice after the des'ired vacuum condition is secured therein and" the mercury flows-through the casing to thebottom. Uponsealing the tubulationand removal of the devicefrom the station, the mercury flows back to the well [5. When the desired final processing of the-device-is attained, the "tubulation '23 is pinch-sealed close to the bottom of the well l5 and a cooling radiator-M having a plurality of fins 25, and advantageously of cast-brass, is mounted on the well by'brazlng to'enclose and protect the exhaust 'tubulation tip ffom damage to theseal. i V The details of the elemental cathode assembly are shown more clearly in Figs. 4 and -5'while Fig." 2"shows the mounting of the cathode'assemb ly in the cathode casing or section. This construction involves an emission source of large capacity enclosed in a double-walled protective andheat conserving housing or enclosure. The cathode assembly is composed of an inner cylindrical metallic shield 26 and an outer shield 21 of larger diameter and both advantageously formed of polished pickel. Theseshields are spaced in coaxiarrelation' by 'a plurality of arcuate wire spacers28 located between the bottom edgesof the shields in such relation thereto that the inner'shield is extended beyond the lower edge ofthe'outer shield. The inner shield is closed at the bottom by a double-walled shielding having one portion formed of an inner flanged disc 29 having a large central opening 30 and a pair of smaller apertures 3| disposed symmetrically across one diameter between the periphery and the opening of the disc. The large opening is closed by a rectangular plate 32 of a gas-absorbing" metal, such as zirconium, so that a large surface of the plate is exposed to the interior of the shield enclosure. An anchor hook 33 is also mounted on the inner shield disc and is equally spaced from the apertures 3|. The other portion of "the bottom shielding assembly is formed of a shield disc 34 having a short peripheral rim 35 an'da pair of apertures 33 adjacent the edge in suchrelation that they are aligned with the apertures 3| in the inner disc. The disc 34 is mounted in nested relation within the inner disc seem their circular areas are in spaced relation equivalent tothe spacing of the cylindrical shields ofthe housing. The nested discs are welded within the lower end of the inner shield 26 and the bottom disc 34 is provided with a plurality of perforations 31 to permit the release of entrapped gases or air within the space between the disc shields.

--' The assembled cathode shield housing, as

above-described, is mounted on a ceramic plate 38'- oi' generally rectangular form with arcuate recessed end portions to accommodate the cylin- "drical'shield housing of the cathode which is -'plate is also provided with holes to receive the terminal conductors 2! which pass through the apertures 3| and 36 in the shield discs and are insulated therefrom by ceramic sleeves or bushings The plate 38 is aifixed'to the con- 'd-uctors by wire clips or staples 4|, as shown in 4: The cylindrical space betweenthe walls 6 oi-=" the---liousing'-may-be filled with: nickel lfoii ribbon l2; as shown in Fig. 2; toincrease -tlie heat conserving properties of the housing? A mesh ribbon-cathodeor filament 43 having an electron 1 emissivecoating,- for example of barium and strontium oxides, is mounted within the housing and ls'formed in zigzag-'orserpertine fashion with the 'plane' surface-ofthe ribbon parallel tothe axisof the housing and the ends formed-to embrace the conductors -2l projecting into the housing. The'ends of the filament are welded to theconductors and'the' center point thereof is secured to the anchor hook 33, to centrally mount the cathode in' the shield housing. In" this position, the mesh filament abuts against the insulating bushings'dil extending into the shield housing with the-edgewis'e mounted folds distributedin' spacedrelation; so that a'copious supply of electrons is emitted from the surfaces ofthe filament' and the emission temperature is maintained substantially uniform by the heat conserving structure of the housing;

A cover or closure portion'isalso provided for the cathodehousing and includes a, pair of annular discs 44 and 45 having flanged rims to fit with in the walls 26 and 21, respectively: Thedepressed position of the inner shild23provides a space equal to the 'spacingbetween the side walls of the housing tocomplete the doublewalled construction surrounding the filament 43 mounted therein. In addition-,- a-pair of 'centrally spaced discs 45-and'41 are mountedwithin the aligned large openings-in-the-closuremem bars by three interposed spaced wires 48 to form an annular channel or passageway 49 for the egress of theelectrons projected'fromthe-"filament under the applied potentials employed in the operation ofthe device.

This construction notonly conserves the heat energy Within the housing fortheeificient operation of the cathode-but also eliminates contermination of the active coating material on the filament by the presence of the gas-absorb ing metal plate 32. The latter is exposed to the interior of the'cas'ing; toreadily'attract spurious gases evolved by the metal parts-when raised to elevated temperatures and preventssuch gases poisoning 1 the activity-7* of the cathodecoating. The e'missive coating on 'the'cathode is also pro-'- tected from bombardment by high potential ionic emission from the otherelectrodesin the de= vice, particularly the anode; since-the construction of'the housing closure forms a protective shield-across the exposed cathode surfaces and thebombarding ions or electrons will strikethe larger areas of the'discs "45 and Hand substantially no projected ions will enter the-restricted annular orifice 49' in the closure-shield portion of the housing. The highly activefilament is therefore protected physically and chemically from injurious 'contaminationsothat along life is "attained in operation.

Another main component'of'the device which forms a part of the casing is the anode section which has a deep-drawn steel cup to with a cenwithin the aperture orthe cup 'fic soth-at'aglass ring 53 may be hermetically sealed to the opposite end, the ring being sealed to a Kovar cup terminal 54 similar to the cathode terminals, previously described. A long central rod 55 extends downwardly from the terminal and has a threaded portion which enters a bushing 56 on the anode, the rod being staked to secure it to the anode. A threaded stud 51 is fastened to the exterior of the terminal to provide attachment for the conductor for the anode. A conical hood shield 58 surrounds the anode lead-in construction and is Welded to the closed end of the anode casing.

The final component of the device is the control or trigger electrode. This involves a relatively thick circular metallic disc 59, preferably of nickel, which forms a separating partition or baiile between the anode and cathode in the device. The disc is provided with circular recesses or grooves 60 and 6 I, as shown in Fig. 3, adjacent the outer edge and on opposite sides thereof, to receive the rim H of the cathode casing and the rim of the anode casing 50 to complete the junction of these casing sections into an integrated enclosure. The heavy disc is brazed to the electrode casings by copper rings inserted in the grooves and fused to the contacting surfaces of the disc and casing sections by heating. The baflfle disc is also provided with a plurality of bisecting slots 62 which form a restricted multiarm passageway of special design in which the width and thickness of each radial arm of the slot provides a control gap having a high gradient characteristic. The discharge current path between the anode and cathode is accurately controlled by providing a conduction discharge gap between any point on the cathode and anode surfaces.

After the slots are formed in the bafile disc and prior to brazing the disc electrode between the other sections of the device, all the surfaces of the disc within the confines of the inner edges of the grooves 60 and GI are carbonized to increase the heat radiation properties of the metal lic electrode. Another distinguishing feature of the control electrode construction, is the exposure of the periphery of the baille disc to the surrounding atmosphere through the rim 63 entirely external to the device whereby the heat dissipating properties of the disc are considerably improved so that the disc runs cooler during operation and secondary emission is decreased. This enhances the control characteristics of the electrode 59 so that a sharp negative cut-off is attained in the operation of the device. Furthermore, the sectional fabrication of the device provides a construction in which the spaced relation of the various electrodes can be accurately controlledduring manufacture since the control electrode disc 59 may be held within close tolerance limits with respect to the cathode and anode and the over-all characteristics of the device will be consistently uniform and stable even though the devices are mass-produced.

Another feature of the construction of the device of this invention is concerned with the mounting support of the device during operation to facilitate the coupling of the device to spaced current conducting bus bars in operational equipment. While the cylindrical casings Ill and 50 surround and enclose the cathode and anode, respectively, within the container of the device, these sections are insulated from the main input and output electrodes by their terminal constructions and the sections form part of the control electrode 59 which is integrally joined thereto at the common intermediate seal between the sections.- Accordingly, the low voltage terminal of the control electrode may be positioned as far as possible from the high potential anode terminal. This is accomplished by placing the terminal studs l4 on the lower closure plate 13 of the device and attaching a heavy steel angle bracket 64 to the studs, as shown in Fig. l, to form the main support for mounting the device in equipment. The filament studs 22 are con nected to flexible copper straps 65 by crown nuts and the anode stud 51 is joined to a similar strap 66. The angle ends of the bracket and straps are all in line and are slotted to facilitate attachment to suitably spaced bus bars and to hold the device in vertical position with sufficient space all around the device to permit free circulation of a cooling medium which dissipates the heat energy expended in the device during operation.

While the complete construction, previously described, forms an efiicient assembly of the device of this invention, some added improvements may be gained from a production standpoint in the fabrication of the cathode section of the device, as shown in Fig. 6. In this arrangement, the casing l8 and closure plate are formed integral by a deep-drawing operation of the steel shell, the closure portion being perforated, as previously described, to attach the terminal assemblies and mercury well thereto and afiix the terminal studs I4 to the closed end of the shell.

An important feature of this embodiment is the prefabrication of the cathode shield housing as a separate unit, shown in Figs. 7 to 9, inelusive, prior to mounting the unit on the conductors 2! in the cathode section. This construction involves an outer cylindrical nickel member 8? which is partially closed at the bottom by a. flanged metallic ring 68 having a large central aperture and a pair of oppositely dis.- posed smaller apertures therein. A thick ceramic ring 69, of high dielectric material, such as a magnesium-silicate composition known as steatite, or other insulating composition, is mounted on the closure ring and carries a pair of metallic sleeves Hi having flanged ends cemented in the recessed apertures in the ceramic ring in alignment with the smaller apertures in the closure ring. A zirconium disc H is superimposed on the insulating ring and fitted over the sleeves and a short inner shield cylinder 12 of smaller diameter than the outer shield is concentrically mounted around the sleeves and provided with a flanged rim [3 which encloses the insulating ring and the flange of the closure ring. When the abutting flanges of the shield and ring are welded together, the disc H and insulator as sembly are securely locked in position. After the folded mesh ribbon filament 43 is secured to the sleeves "Hi the whole assembly is inserted into the bottom of the outer shield 61 and welded to the lower edge thereof. In this construction the disc H performs the same function as described in connection with the plate 32 in Fig. 5 since its surface is exposed to the interior of the shield housing close to the active cathode coating.

The cathode housing is completed by a closure disc M having a flanged rim 15 welded to the inner edge of the top of the outer shield 61 and carrying a depending inner shield cylindrical portion 76 which enters the housing and is in telescopic relation to the shield cylinder 12. The portion 16 is secured to the closure disc by raised emboss ments 11 distributed in spaced re,-

.9 latio'n .onnthe toptohztheeshieldrportions andf thesezemhossmentszareavelded tocthesiowemsure face otthe iclosurezdisc imccncentrim'relation; so: that. theicylindricalzwalle ofuthe' shield-sis zuniel for-mlypspacedzwith respecti-to thercoaxial sur. faces :of the'ehi'eld portionrnnmttthe ou-tenshieldov cylinder 8?; Both: the :closurer disc :14 a11d:.de-; pendingshieid-rportiom.T'Erareeprovided .w-ith. ans-- nular segmental aligned orificesirl8; shownzimore clearly-infE-ig'. 9; binfcentral disc portions 19 and 80,.,re'spectively', 'which are integrally joined to theiemain' parts :byiclfannel-shaped radial arms at. These arms may be formed by bending the sides on each arm in opposed relation so that tlieiiumeeting; edges ,formziatclosedor split Joint to increase the structural strengthof [the small.- spaced disc portions l9 and 8d and provide a discharge gap of 'annular configuration for the projecticnzof the electrons fromthe cathode. en:-

clusediin the-; housing....

' The Fcathode unit .is. mQIlBtB'dQOII the acomiu'ce tors] extending, intothelcath'ode. 'sectioniof the device shy, :wslding .the sleeves: I I3 .to the ccondu'cet tQP-SS' An additional gas-.absorbingi'strip 82;: prefr erably of pure zirconium metal, may be attached to the inner wall of the cathode casing, as shown in Fig. 6, to absorb gases given up by the casing walls and other elements and thereby preserve the purity of the vapor employed as the ionic conducting medium in the device.

While the disclosure is of certain specific embodiments to show the various features and advantages of this invention, it is, of course, understood that structural modifications may be made in the constructions shown to attain the results of this invention without departing from the scope and spirit of this invention as set forth in the appended claims.

What is claimed is:

1. A shielded cathode assembly for electronic discharge devices comprising a double-walled cylindrical metallic casing having apertured end closures, folded ribbon filament mounted therein, supports for said filament extending through one of said closures, and a gas-absorbing metal element extending across an opening in said closure and exposed to the space within said casing.

2. A shielded cathode assembly for electronic discharge devices comprising a double-walled cylindrical metallic casing having end closures, a folded ribbon filament mounted therein, supports for said. filament extending through one of said closures, and a strip of zirconium metal attached to one of said closures and exposed to the space surrounding said filament.

3. A shielded cathode assembly for electronic discharge devices comprising a metallic casing having spaced cylindrical double-wall portions, spaced disc platform members closing one end of said portions, said members having aligned pairs of apertures and the inner member having a central opening, spaced annular disc cover members extending across the opposite end of said casing portions, a pair of central bafile plates supported in concentric position in said cover members, a pair of supports projecting through said aligned apertures, a folded ribbon filament mounted on said supports and enclosed in said casing, and a layer of zirconium metal secured to the inner platform member and clossaid central opening.

4. A high power grid-controlled mercury vapor rectifier device comprising a cylindrical metallic casing formed of two superimposed sectionazan ancdevsupported within ones section: and insulatingly mounted: fromaa: terminal at: theaclosed? end thereof; a'zshielded filament :as-

sembly extending into the "other section: and superported-.1 on: insulated terminals projecting from-5: the closed end: remote-fromzsaid anode terminal; armeroury well joined. to the; same: closed end: and-cofiset with respect to-saidihsulat d termin rials; a imetallic ,igrid :disc having. a central openeing r'sealed between. said "sections and .formingrar. partionsaidcasing; terminal posts on the closed: end! of the' filament:supporting rsectionaforisaidc grid: and iofisetzangularzmounting con-ductorsrsee cured? to saidwian'ode: terminal, ofiset angular? mounting conductors' securedsto eachnof'; saids filament terminals; .and ."a-zheavy bracket securedi toesaid Fgrid 1- terminals-posts, said bracket bein'g'i adjacent said second-mentioned" mountingycon ductorsa. 1 1 I 52-.A high" power gridecontrol'ledz mercunye vapor rectifier. 1* device; comprising a cylindrical; metallic casing; formed of twowsuperimposedsec-e tionsaarranodezsupportedrwithinsone section and-1 insulatingly' 'mounted? from 1 as. terminal at closedendcthereof; a shielded: filament sassemblyr;

extending into the other section and supported on insulated terminals projecting from the closed end remote from said anode terminal, a mercury well joined to the same closed end and offset with respect to said insulated terminals, a metallic grid disc having a central opening sealed between said sections and forming a part of said casing, and a conical hood shield surrounding said anode terminal and secured to said casing.

6. A shielded cathode unit for electronic discharge devices, comprising a cylindrical metallic casing, a perforated closure on one end, an apertured insulating disc superimposed on said closure, a pair of sleeve members mounted in said disc and aligned with the openings in said closure, a gas-absorbing metal plate abutting against said disc, a folded ribbon filament disposed within said casing and attached to said sleeve members, and an apertured cover on the opposite end of said casing.

7. A shielded cathode unit for electronic discharge devices, comprising a cylindrical metallic casing, a perforated closure on one end thereof, an apertured insulating disc superimposed on said closure, a pair of sleeve members mounted, in said disc and aligned with the openings in said closure, a zirconium plate abutting against said disc, a folded ribbon filament disposed within said casing and attached to said sleeve members, an apertured cover on the opposite end of said casing, and a cylindrical shield within said casing joined to the closure assembly.

8. A shielded cathode unit for electronic discharge devices, comprising a. cylindrical metallic casing, a perforated closure on one end thereof, an apertured insulating disc superimposed on said closure, a pair of sleeve members mounted in said disc and aligned with the openings in said closure, a folded ribbon filament disposed within said casing and attached to said sleeve members, a plate of zirconium metal within said casing and opposite said filament, an apertured cover on the opposite end of said casing, and a pair of oppositely disposed telescoped shield 'members within said casing surrounding said filament.

9. A shielded cathode unit for electronic discharge devices, according to claim 8, in which 11 said shield members are supported by said closure and cover respectively.

10. A'shielded cathode unit for electronic discharge devices, comprising a cylindrical metallic' casing, a perforated closure on oneend thereofian apertured insulating disc superimposedfon said closure, a pair of sleeve members mounted in said disc and aligned with the openings in 'said closure, a gas-absorbing metal plate abutting against said disc, a folded ribbon filament disposed with said casing and attached to said sleeve members, an apertured cover on the opposite end of said casing, said'cover having a central aperture and a flanged rim, an integral disc within said central aperture, and reinforcing arms extending radially between said latter disdand cover, said rim being joined to the inthe bottom of said shell, afpair of metallic members'f having flanged rims disposed on opposite sides of said disc, the rim of one of said members overlapping said disc and the other member and being Joined to the inner surface of said shell, a zirconium plate superimposed on said disc, a pair of metallic sleeves mounted on said disc and extending within said shell, a ribbon filament of zigzag formation attached to said sleeves, and a double-layer cover having an annular orifice connected to the opposite end of said shell, said cover having a depending shield portion surrounding said filament.

PAUL R. MENZEL.

VICTOR L. RONCI.

ROBERT L. VANCE.

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

UNITED STATES PATENTS Number Name Date 2,078,123 Cage Apr. 20, 1937 2,206,710 Tonks July 2, 1940 2,292,081 Maser Aug. 4, 1942 2,306,808 Hutchings Dec. 29, 1942 2,356,566 Clark et a1 Aug. 22, 1944

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