US2435246A - Gaseous discharge device containing perforated starting electrodes - Google Patents

Description

Patented Feb. 3, 1948 GASEOUS DISCHARGE DEVICE CONTAINING PERFORATED STARTING ELECTRODES Paul W. Stutsman, Needham, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application February 14, 1946, Serial No. 647,463

4 Claims. (Cl. Z50-27.5)

This invention relates to gaseous discharge devices, and more particularly to such devices employing, in addition to a cold cathode and an anode, a starting electrode.

Apparatus such as television, radar, electron microscopes and kindred devices employing relatively high potentials and comparatively small currents, usually entails the use of power supplies incorporating, in addition to the high tension transformer, rectifying devices which require a filament supply, said filament supply being heavily insulated against the high pote-ntials used in the aforementioned apparatus. It can be readily observed that such combination adds considerable bulk to the apparatus under discussion, greatly increases the cost and limits the portability of same.

The expression relatively high potentials refers to a range of such potentials which may be at least 1,000 volts and higher.

It is a principal object of this invention to provide a device of the type described which shall be diminutive in size with respect to its ability to handle relatively high voltages.

Another object of this invention resides in the use of a cathode which has a diameter substantially that of the envelope enclosing same, said cathode having an electron-emissive material affixed thereto which can be evolved at a temperature which is lower than the softening point of said envelope.

A still further object is to provide a device of the type described having, besides the two main electrodes, a third electrode spaced a distance from the effective area of one of said electrodes substantially equal to the minimum breakdownpotential distance of said device, the distance between the effective area of said main electrodes being substantially diierent from the minimum breakdown-potential distance.

Another object of the device provides for the use of an electron-emissive material affixed to the starting electrode and placed in the path of discharge between the main electrodes whereby said discharge evolves the electron-emissive material and prolongs the usable life of said device.

These objects are attained in accordance with the general aspect of the invention by providing a device having a cylindrical envelope containing a cathode whose diameter is substantially that of said envelope and because of this close spacing between said envelope and cathode, providing, in one embodiment thereof, a device having overall dimensions which are approximately three quarters of an inch in diameter and two and one eighth inches long, and a second embodiment in which the arrangement of the electrodes therein provide a device which is approximately a half of an inch shorter than said first-mentioned embodiment. Despite the relatively small size of the aforesaid device, it is capable, in this particular embodiment, of withstanding inverse voltages of the order of 2,700 volts and can furnish a rectified output of about 1,000 volts, the device being a cold cathode type that does not require a filament transformer or other source of lilament supply. This feature, coupled with its diminutive size, permits construction of power supply units of relatively small dimensions. By wiring the tubes in cascade, rectification of potentials employed in television, radar, electron microscopy and related high potential operated systems is readily accomplished.

These and other features and advantages of the invention are more clearly set forth in the following detailed description which, together with the accompanying drawing, represent various embodiments of the device of this invention.

In said drawing:

Fig. 1 illustrates one embodiment of the device in perspective and partial cross-section;

Fig. 2 represents a second embodiment presented in the same manner as Fig. 1; and

Fig. 3 is a schematic diagram of a rectifying circuit employing the present invention.

Referring now more particularly to Fig. 1, the device comprises a vitreous envelope Ill, containing an ionizable gas, preferably xenon, at a, pressure of about 14 mm. of Hg. A base I I of similar material is fused to one end of said envelope Ill for supporting various electrodes within said envelope and a plurality of conductors I2 are sealed in said base i I for conveying energy to said electrodes. The other end of said envelope is provided with a central conductor I3 placed Within a sleeve member lli and both sealed in said end of envelope. An output electrode or anode I5 which cooperates with the electrodes supported in said base Il is connected within the other end of sleeve member It.

The anode I5, as illustrated, comprises a rod, preferably composed of carbon. It Was observed that carbon has a lower sputter rate than refractory metals, although the anode may, if desired, be formed of a refractory metal. Surrounding the anode yIii is an electrically-conductive member I6 which is insulated from the anode I5. Member I 6 acts to shield the cathode IB from having deposited thereon sputtered material which may be released from the anode I5. Such 3 material, if deposited on the cathode I8, greatly diminishes the emlssive life of said cathode. The distance between the last-named members I5 and I6 is sufiiciently small so that a discharge will not ordinarily occur in the space between them. A vitreous sleeve I'I surrounds the members I5 and I6. The function of member i1 will be treated further along vin this specification. The member I1, in this particular embodiment, is integral with the envelope Ill.

The hollow metallic member or cathode I8, preferably made of nickel, is maintained in axial alignment with respect to the other electrodes by spacers I9. Fixed within said cathode is an annular metallic member made of nickel (other metals such as cobalt steel or iron may be used) for supporting, on its inner surface, hollow iron wire members 2| which contain therein an electron-emissive material (not shown). Means for readily releasing said electron-emissive material is provided by regularly spaced apertures 22. Positioned within said cathode I8 is a third electrically-conductive electrode 23 which will be referred to hereinafter as the starting electrode. The starting electrode 23 is connected to conducting member I2 through a helical metal spring member 24. The member 24 serves a two-fold function; first, as a positioning means to maintain starting electrode 23 in axial alignment with respect to the vitreous sleeve 25, and second, to permit expansion and contraction of member 24 without undue strain on said sleeve 25. Member 25 prevents sputtered material from members 2l and 26 being deposited on electrodes I8 and 23 and forming short circuit paths therebetween. How this feature is accomplished will be explained further along.

Aflix'ed to and extending at right angles from starting electrode 23 is a hollow iron wire member 26, said member being a part of said starting electrode. Within said hollow iron Wire memberv 26 is placed a quantity of electron-emissive material (not shown) which is released through the apertures 21 shown in said hollow iron wire member 26. The method by which the electron-emissive material is released will be pointed out hereinafter,

In the particular embodiment illustrated in Fig. 1, the vitreous sleeve member 25 is fastened to the base II by means of a suitable cement 2,8. However, the sleeve 25 can be fused to the base II directly, in which case, the positioning member 24 could be eliminated. f

The particular arrangement of electrodes illustrated in Fig. 1 is known to the art as a doubleended device, Whereas, Fig. 2 illustrates what is now known as a single-ended device, the latter expression indicating that connections to all the electrodes are made at one end` in contra-distinction to the double-ended device shown in Fig. 1.

With the exceptions of the position of anode I5 in Fig. 2, the use of only one spacer I9, and the use of a reentrant tubular member I 8A, the second embodiment is substantially the same as illustrated in Fig, 1. Therefore, the reference numerals applied to Fig. 1 areA equally applicable to of the device in order to present a more detailed view of the structures therein. l

A principal feature of the present invention is its diminutive size and the advantages accruing to such construction. The relatively small space between the cathode and the envelope presented a problem inasmuch as it was necessary to apply v tron-emissive material, Aand to drive out the gases from the supports holding said electron-emissive material andthe other electrodes. It was found necessary to evolve only a relatively small amount of the electron-emissive material during the manufacturing process, the balance of the activating material being evolved during the operation o f the device by bombardment from the 'positive ions present in the discharge. This arrangement serves to simplify the manufacture of the device with respect to time required for processing the tube. It was observed that the use of a exible metal strip 20 made of nickel for example, as a support for the hollow iron wire members 2 I, provided a more satisfactory means of attaching said hollow iron wires 2l to the inner surface of the cathode I8. To attempt to weld the wires 2l directly to the cathode I8 would result in serious damage to said cathode as the heat required to make this weld causes a reaction between the iron wires 2i, the cathode I8, and the active material within the iron wires 2| that results in burning a hole in the cathode material. This condition would permit the emissive material to leak outside of the cathode chamber I8 Where its usefulness would be lost and in addition such burns would impair the appearance of the cathode. However, by first welding the iron wires 2I to the annularv strip 2Il,.it was then possible to weld this strip 20 to the cathode I8 without destroying the surface of the cathode I8 at the point of weld. In addition, it was less awkward to weld the iron Wires 2I to the strip than it would be to weld the iron wires 2I directly to the inner surface of cathode I8. The prior art teaches the use of methods in which the cathode is sprayed with the activating material such as barium or strontium carbonates or is dipped in such active material. This method requires the application of temperatures in the range of 1,000 or 1,100 degrees centigrade to drive out the unwanted gases and must be applied over extended periods of time. Temperatures such as these when used to heat the base metal, upon which the electronemissive material is coated, radiate enough heat to soften the envelope if it were not spaced a suiiicient distance from the heated metals. The advantages of the present device are readily appreciated in view of the recited prior art.

Another feature which gives added life to the device is the use of a starting electrode having aiiixed thereto a quantity of electron-emissive material. On the inverse or negative cycle, the starting electrode behaves like a cathode and is consequently subjected to positive ion bombardment. This action evolves the active material onto the cathode surface. Added cathode surface is made available by the reentrant tubular member IBA as illustrated in Fig. 2, said tubular mememissive material from the starting electrode extension member 2B.

Still another feature ofthe present invention is the space relation of the starting electrode 23 l amazes with respect to the cathode I8 and. anode I5.

The starting electrode is spaced a distance from the effective area of the cathode, substantially equal to the minimum*breakdown-potential disf tance of the device. The minimum breakdownpotential distance is deiined herein as that distance at which a discharge will be initiated between twol electrodes for a minimum applied potential. However, the anode is spaceda distance from the effective area of the cathode substantially different than the minimum breakdown-potential distancebetween the starting electrode and the effective area of the cathode, the distance being such with respect to the cathode that the anode can handle large inverse voltages. The aforementioned arrangement of the starting electrode with respect to the cathode permits a lower starting voltage for the device.

In connection with the spaced relation of the electrodes, particular attention is called to the novel construction of the starting electrode. The member 26 which is part of the starting electrode is spaced with respect to the anode l so that, when the initial glow discharge takes place between itself and the cathode, the potential on the anode becomes greater than the potential on the starting electrode, and the anode` consequently pulls electrons out of the plasma surrounding said starting electrode, and as a result the main glow discharge is more readily accomplished. In order to maintain the initial glow discharge between starting electrode and cathode,

in the vicinity of the anode, a vitreous sleeve member 25 surrounds that portion of said starting electrode 23 which is parallel With respect t0 the cathode I8. This arrangement contines the glow discharge to the portion 26 of the starting electrode and brings about the desired result mentioned above. The sleeve member 25 appreciably surrounds the entire starting electrode 23 to the junction of said electrode and the extended member 26. This sleeve arrangement prevents the deposit of sputtered material on lsaid starting electrode 23 and therefore inhibits the possibility of an electrical short circuit between itself and the cathode I8. l

In explanation of the difference of potential between the anode I5 and starting electrode 23, reference is had to Fig. 3. During those portions of the cycle when no appreciable current flows between cathode and starting electrode, the potentials on'the anode and starting electrode are the same. However, when the glow discharge between the starting electrode 23 and cathode I8 takes place, current flows through resistor 30,

which can have a value of about ten megohms,

so that the resulting potential drop across said resistor lowers the potential on said starting electrode 23 with respect to said anode I5. The resistor 30 also serves to protect the member 25 from excessive currents during the inverse or non-conducting period of the device which may easily destroy said member 26.

A further advantage of the member 2S attached to starting electrode 23 is the use of this member as a support for electron-emissive material. The position of said member 26 in the path of the discharge enables it to increase the emissive capabilities of the cathode, especially that of the 6 effective area of the cathode represented bythe reentrant tubular member I8A, Fig. '2. The electron-emissive material is readily` released from the apertures 21 by the ionic bombardment during the discharge period and is sputtered therefrom on the cathode area IBA.

While Fig. 3 .illustrates the use of four devices in cascade. it can readily be observed by those skilled in the art that at any desired magnitude of voltage rectification, the requirement would be n times 1,000, where n equals the 4,number of tubes and 1,000 equals the rectified voltage output of each tube in this particular embodiment. Y The use of gaseous discharge devices as rectiiers in connection with commercial power supply line frequencies is well known. However, attempts to use these devices in' connection with radio frequencies have not met with much success. One of the limiting factors has been the time required for ionization and deionization. This limitation is quite marked in gaseous discharge devices operating at high pressures, for example, at pressures of about 14 mm. of Hg. At such pressure the deionization takes place at a relatively slow rate, so that the deionization time v may be as long as 1,000 microseconds or longer.

Ordinarily, the ionization time ranges from 1 to 50 microseconds.. In both instances the element of time above mentioned would represent a severe limitation to the operation of gaseous discharge devices at radio frequencies.

In the present device the design and correla tion of the electrodes permit the handling of current at radio frequencies regardless yof the limitations above recited, such limitations being overcome in the following manner. When the device is made conducting the starting electrode 23 initiates the discharge and the anode I5 subsequently takes over the function of the main discharge. As a result, the plasma in the region between the anode I5 and cathode I8 will have a substantial positive ion'population. When the anode becomes negative, the electrons are repelled therefrom, and positive ions in the vicinity of said anode I5, the anode shield i6 and sleeve member I'I will form a positive ion space charge. As a result, the field strength of the inverse potential of the anode will be greatly nullified exteriorly of member I'I, this condition in turn reducing the mobility of the positive ion popuknon-conducting cycle, in the present case this condition is used to advantage. On the positive cycle, the presence of the previous positive ion population serves to lower the reionization time and required voltage. It can be readily discerned that the process of reducing the mobility of the positive ions, brought about by the creation of the positive ion space charge inthe vicinity of the anode, prevents destructive bombardment of the anode during the non-conducting portion of the cycle and so conditions the interelectrode space that, upon the succeeding positive portion of the cycle, conduction of current is provided.

It follows that regardless of the rapidity o! change of polarity lon the anode, adequate protection on the inverse or negative portion of the cycle is provided and suilicient ions to provide a conducting path on the forward or positive portion of the cycle will always be present.

Although several embodiments of this invention have been described and illustrated, it is of course understood that many modifications and alterations may be made wherein the relation of the electrodes may be altered to effect the primary conception of this invention. For example, the eiective cathode area can be made larger, en-

abling the device to handle heavier current, this alteration being possible without substantially increasing the overall size of the device.

1..A gaseous discharge device comprising an envelope containing an ionizable gas, a plurality of electrodes supported within said envelope, said electrodes comprising an anode and a cathode therefor, and a third electrode, said last-named electrode having aiixed thereto a hollow metallic tubular member, perforated at intervals, and containing an electron-emissive material therein, said last-named member being disposed in the path of a discharge between said anode and cathode, whereby said electron-emissive material is evolved by reason of the temperature normal in a discharge between said anode and cathode.

2. A gaseous discharge device comprising an envelope containing an ionizable gas, a plurality of electrodes supported within said envelope, one of said electrodes comprising a relatively large hollow metallic cathode, a at annular member attached to the inner Wall of said last-named electrode, and a perforated hollow wire containing an electron-emissive coating material therein. said wire member being attached to the inner surface of said annular member.

3. A gaseous discharge device comprising an envelope containing an ionizable gas, a plurality of electrodes supported within said envelope, one of said electrodes comprising a relatively large hollow nickel cathode, a nat annular member of nickel attached to the inner wall of said lastnamed electrode, and a perforated hollow iron wire containing barium metal therein, said wire member being attached to the innersurface of said annular member.

4. A gaseous discharge device comprising an envelope containing an ionizable gas, a plurality of electrodes supported within said envelope, one of said electrodes being surrounded by an electrically conductive shield extending above said first-named electrode and open at its upper end, means for insulating said shield from said firstnamed electrode, an insulating member, open at its upper end, surrounding said first-named electrode and shield member, and another of said electrodes adiacent the openings of said shield and insulating member and facing said rstnamed electrode.

PAUL W. STUTSMAN.

REFERENCES CITED The following references are of record in the 111e of this patent:

UNITED STATES PATENTS Rentschler Aug. 30, 1932

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