US2636145A - Gaseous discharge device - Google Patents

Description

Patented Apr. 2l, 1953 `UNITED STATES `Pill'liENT OFFICE AGrA'SEQUS DISCHARGEDEVICE I'Paul `W. 'Stutsmam i Needham, Mass., assigner 'to Raytheon Manufacturing Company, Newton, \Mass.,.a corporation of Delaware Application August 31, 1949, Serial No. 113,349

(Cl. S13-198) '5 Claims.

This application relates to gaseous discharge devices Vand more particularly to structuressuitablefor subminiature tubes of relatively large current capacity. p

In the design of cold cathode tubes, Ythe problem of producing suflicient cathode area in a small tube, for example, of the sub-miniature type, has materially limited the average andpeak `current capacities of these devices. In addition `the use oi large cathodes creates a serious problem 'of shielding the cathode from the anode to prevent inverse current discharges and loss of vgrid control for forward discharges.

Applicant has produced a device utilized, by way of example, in a rectier which has a large cathode surface such that large peak and average currentsmay be drawn from this cathode. To do this applicant has made a hollow cathode substantiallylling the entire envelope of the device and has positioned the anode inside this cathode. In addition the area of the cathode has been further increased by placing a second cylinder inside the rst for a portioncf the length thereof, fboth cylinders being coated with electron emissive material. This necessitates the positioning of the anode structure inside `a hollow cath-ode and, to prevent inverse discharges between the anode and cathode for relatively high voltages, applicant provides for the anode 4to be shielded by electrostatic and .dielectric shielding structures.

Since this anode shielding substantially reduces the potential gradient between the anode and cathode, applicant provides a novel means of starting the. dischargebetween the` anode and cathode during the application of positive po tentials to the anode and negative potentials to the cathode. This starting means comprises an auxiliary electrode positioned between the anode and cathode, such that the dielectric and electrostatic shields surrounding the anode do not lie between the auxiliary electrode and the anode or the auxiliary `electrode andthe cathode. Applicant provides electron emissive material on the auxiliary electrode so thata relatively low potential gradient produced in the gap between the anode and the auxiliary electrode, or the cathode and `auxiliary electrode, will produce a discharge, thereby supplying electrons and posifthe cathode andthe anode. One species of this devicewvill now bedcscrib'ed in detaiL'reference being had to the accompanying drawings where- Figl is a longitudinal cross-sectional viewmof a device embodying applicants invention taken alongline I-I of Figuz; v

Fig. 2 is a transverse cross-sectional viewiof Vthe device shown in'Fig. 1 taken alonglinel-Z of Fig. l; and

Fig. 3 is an illustrativeexample of fa circuit wherein this device may be used.

Referring` now to 'Fig 1, "there is shown van envelope IIJ comprisingfa substantiallytubular memberwhich maybe of, for examplaglass. The upper end of the tubular envelope I Il is fused togetheras at I I and has extending therethrough a metallic conducting member I2, said conducting member being substantially coaxialwith the-tubular envelope I. Attached to thelower orl'iinside end of 'the conducting memberIfZ isa carbon rod I3 whose diameter is-substantiallyequal to that of conducting member i2, saiddiameter-being, for example, approximately one-tenth the diameterof' theV tubular envelope I0. The carbon member is held tothe conductor member-I2 by a short metallicsleeve I4 extending overlthe lower end of conductor I2 and a portionoffthe carbon rod I3. The lower end of the rod 'I3 is positioned about one-fth of the length 0i ene velope IEl down from the glass seal I I.

Surrounding sleeve Ill,` carbon rod I3 and the lower end of conducting member I2 is an electrostatic `shield comprisinga metallic cylinderl I5 slightly larger in diameter than sleeve i4. Cylinder I5.is rigidly positioned by having the upper end imbedded in glass seal II. Cylinder I5 does not touch the anode assembly I2, I3 and I4 and extends downward from Aglass seal ll I beyond the lower end of carbon button I3 for a distance approximately equal toits own diameter.

Surrounding shield I5 is a dielectrcmember I6 comprising a glasstubewhose upper end `is fused to the 4glass seal vIl and which extends downwardly therefrom coaxial with carbonbutton I3, metallic rod I2 and shield I5 for a`dis tance somewhatV less 'than the diameterci shield I5 below the lower end of shield I5.

Surrounding the glass tube 'I6 is a cathode structure il comprising aV cylinder I8 coaxial therewith and whosediameter is Vapproximately `twice the diameter of glass tube I6. The cylinder it extends from a point substantially above the `lower end of carbon button -I3 downwardly to `a point adjacent the low-er'end "offenvelope i t. The upper end ci cylinder I 8' is 'substantially closed -by -an end `plate IEhav-ing an `aperture therein suicient to allow the passage of the glass tube I3 therethrough. Above end plate I9 is positioned a mica spacer 29 in the form of a ring, the outer edge of which rests against the inside of envelope It and the inside hole of which surrounds and is in close proximity to the outside of the glass tube I3. The mica spacer 29 is attached to cylinder I8 by metallic tabs 2| welded to cylinder I8 and extending through apertures in the mica spacer 20. The lower end of cylinder I 8 is maintained in position by resting against a mica spacer 22 substantially similar to spacer 29. Extending through spacer 22 are tabs 23 which are welded to cylinder I8 and to lead-in wires 24 which extend through a glass press 25 sealing the lower end of envelope I0.

Extending upwardly from glass press 25 through mica spacer 22 is a glass tube 25 which is coaxial with envelope II) and the carbon button I3. The diameter of glass tube 25 is approximately equal to the diameter of the sleeve I4 and the upper end of tube 26 is positioned somewhat below the lower end of the tubular shield I; for example, approximately the diameter of the tubular shield I3 separates the ends of the aforementioned tubes.

Extending upwardly through tube 23 and glass press 25 is a lead-in rod 21 which is positioned concentrically inside glass tube 26 by means of a spacer 39 comprising several turns of wire helically wrapped around member 29. Rod 29 extends slightly beyond the end o f tube 26 and terminates in electrode 3I comprising electron emissive material. Electrode 3l is shown here, by

. way of example, `as al short piece of straight wire Welded to the end of rod 29 and at right angles thereto. The wire is hollow and contains electron emissive material such as barium carbonate which is exposed through the upper side of the wire through nicks cut therein. The length of the wire electrode 3| is slightly greater than the diameter of glass shield I6.

Surrounding glass tube 26 is a metallic cylinder 32 whose diameter is approximately twice the diameter of glass rod 26, the relative coaxial position of members 26 and 32 being maintained by a spacer 33 similar to spacer 30 but whose turns are somewhat larger in diameter. The lower end of cylinder 32 is attached as by welding to an end plate 34 which closes the lower end of cylinder I8.

Inside cylinder I8 at approximately the midpoint thereof, said midpoint being substantially below the upper end of cylinders 23 and 32, is positioned several turns of wire 35 of the same type used for electrode 3 I.

After the tube has been assembled but before Athe gaseous filling has been admitted, the wire turns 35 are heated in a vacuum, for example, by R. F. induction heating whereby the electron emissive core of wire 35 is evaporated. This electron emissive material then condenses on the inner surface of cylinder I8 and the outer surface of cylinder 32 .as well as upper and lower end plates I9 and 34 such that these surfaces become an active part of the cathode, thereby producing a cold cathode having an extremely large emitting surface and hence a high peak and average current capacity.

Since `the carbon button I3 is shielded by the metallic tube I5 and the dielectric tube I6 from direct exposure to any cathode surface, the potential gradient in the gaseous medium between the cathode and the anode button I3 is relatively low for high voltage differences therebetween. In

order to allow the tube to conduct readily for relatively low forward voltages between the anode and the cathode, auxiliary electrode 3I is positioned directly below the anode button I3. Since the shield members I5 and I6 are not positioned between anode button I3 and the electrode 3|, a relatively low potential between these two electrodes will produce a suiciently high potential gradient to ionize the space therebetween so that by an appropriate circuit the tube may be fired.

Referring now to Fig. 3, there is shown, by way of example, a circuit using the discharge device illustrated in Figs. 1 and 2. The cathode I'I is connected to ground through a condenser 36 of, for example, 4 microfarads across which is attached the output load 3l shown here, by way of example, as a resistor of 50,000 ohms. The auxiliary electrode 3| is connected to ground through a current-limiting resistor 38 of, for example, 10 megohms. The anode I3 is connected through a peak current-limiting resistor 39 of, for example, 2,500 ohms, to a source of alternating current which is to be rectified. This source, as shown here, is a transformer 40 whose secondary 4I is connected from ground to resistor 39 and whose primary 42 is connected to a source of alternating potential.

In this particular circuit, when the ungrounded end of transformer secondary 4I is driven positive, a discharge will occur between anode I3 and cathode Il charging the condenser 36 such that the side thereof connected to cathode I'I will be positive with respect to ground. This potential will be partially dissipated through resistor 3'I between cycles of the alternating current. The result is that the cathode II will be at all times more positive than the electrode 3| which is connected to ground through the resistor 38. This potential between cathode I'I and electrode 3! causes the electrons emanating from the electron emissive matter of electrode 3| to flow from electrode 3| to the cathode I8, thereby Aproducing a keep-alive discharge. This keep-alive discharge creates a large quantity of free electrons in the vicinity of electrode 3I, said electrons being readily drawn to the anode I3 upon the application of a relatively low positive voltage to anode I3. When anode I3 is driven negative during the negative portion of the alternating current cycle of the source, the potential of the cathode I 8 is shielded from the anode I3 by members I5 and I6 such that a higher peak inverse voltage may be applied between anode I3 and cathode I8 without an inverse current breakdown. Since electrode 3| is at a considerably lower potential than cathode Il, for example, near ground potential, the peak inverse voltage between electrode 3l and the anode button I3 is considerably less than the peak inverse voltage button cathode I8 and anode I3 with the result that breakdown does not occur therebetween.

This completes the description of the particular modification of the invention illustrated herein. However, many modications thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, the tube may be operated by attaching the electrode 3I to the anode I 3 or to the cathode Il, and various sizes and shapes of electrodes as well as different materials may be used without departing from the spirit and scope of this invention. Therefore, applicant does not wish to be limited to the particular details of the species of the invention described herein except as dened by the appended claims.

What is claimed is:

1. An electron discharge device comprising an envelope containing a gaseous medium, an anode, an auxiliary electrode, and a cathode comprising a first hollow cylindrical member substantially surrounding said anode member and said auxiliary electrode, and a second hollow cylinder positioned inside said first cylinder substantially coaxial therewith and substantially surrounding a portion of said auxiliary electrode, the inside of said rst cylinder and the outside of said second cylinder having electron-emissive material coated thereon.

2. An electron discharge device comprising an envelope containing a gaseous medium, an anode comprising a rod, a cathode, and an auxiliary electrode positioned adjacent said anode substantially coaxial therewith, said auxiliary electrode having a metallic support connected thereto, said support being surrounded by an insulating sleeve, the portion of said insulating sleeve adjacent said auxiliary electrode being surrounded by a metallic sleeve in close proximity thereto but insulated from said auxiliary electrode, said auxiliary electrode having an exposed area of electron-emissive material thereon.

3. An electron discharge device comprising an envelope containing a gaseous medium, an anode substantially surrounded by a metallic sleeve and an insulating sleeve, a cathode, and an auxiliary electrode, a supporting portion of said auxiliary electrode being substantially surrounded by an insulating sleeve coaxial therewith, said cathode comprising a iirst hollow member substantially surrounding said anode member and said sleeves, and a second hollow member having an electronemissive coating thereon and positioned inside said first member spaced therefrom, said second member having therein said supporting portion of said auxiliary electrode.

4. An electron discharge device comprising an envelope containing a gaseous medium, an anode,

a cathode, and an auxiliary electrode, said cathode comprising a iirst hollow cylindrical member substantially surrounding said anode member, and a second hollow cylinder positioned inside said first cylinder and substantially coaxial therewith, said second cylinder having therein a support member for said auxiliary electrode, said support member being surrounded by an insulating sleeve and being substantially coaxial with said anode and cathode.

5. An electron discharge device comprising an envelope containing a gaseous medium, an anode, a cathode, and an auxiliary electrode positioned adjacent said anode, said auxiliary electrode having an exposed area of electron-emissive material thereon, said anode comprising a rod, and an insulating sleeve substantially surrounding said rod, said cathode comprising a rst hollow cylindrical member substantially surrounding said anode member and said sleeve, and a second hollow cylindrical member positioned inside said first member and substantially coaxial therewith but spaced from said cathode, the inside of said first cylinder and the outside of said second cylinder having electron-emissive material thereon, said second cylinder having therein a support member for said auxiliary electrode, said support member being surrounded by an insulating sleeve and being substantially coaxial with said anode and cathode.

PAUL W. STUTSMAN.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,749,611 Schroter Mar. 4, 1930 1,986,397 Hund Jan. 1, 1935 2,033,089 Bahls Mar. 3, 1936 2,206,008 Spencer 1 June 25, 1940 2,435,246 Stutsman Feb. 3, 1948 2,462,142 Stutsman Feb. 22, 1949

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