US1902482A - Electron discharge apparatus - Google Patents

Description

Mfi 1, 1933- M. A; AcHEsoN-Er AL I ELECTRON DISCHARGE APPA'RKTUS Filed Sept. 4, 1928 Inventors: Marcus A. Acheson; James L. Zehner, y $550M His A torney.

Patented Mar. 21, 1933 UNITED STATES? main PATEN MARCUS A. AGHESON ANT) JAMES L. ZEHNER, OF SCHENEGTADY, NEW YORK, ASSIGNORS TO GENERAL ELECTRIC COMP-AN Y, A CORPORATION OF NEW YORK- ELECTRON DISCHARGE APPARATUS Application filed September The present invention relates to electron discharge apparatus and more particularly to devices in which the current is carried principally by electrons but which contain a relatively, small amount of ionizing vapor for reducing space charge. In thermionic devices that employ, inter alia, an electronemitting cathode, an anode and mercury or other form of ion-producing vapor forthe.

purpose stated, the mercury has heretofore been introduced into the envelope as a liquid which collects as a small pool or globule at the bottom of the container. The reduction of space charge by means of an ion-producing vapor with which th-e subject-matter of the derived from a heated body, usually a filament, the magniture of the particle stream,

hence, the current-carrying capacity of the device, is limited strictly to the electronemitting power of the filament. of space charge in such devices is to produce a curtailment of the particle stream, so strong under certain conditions as compared with the limited number of electrons present,-as substantially to prevent further current flow, The introduction of mercury or other easily ionized vapor into the envelope is simply for the purpose of removing this efi'ect so as to allow the electrons emanated by the filament, to flow more freely across the evacuated space. On the other hand, mercury arc devices do not employ electron emitters of the heated solid body type and the stream is not of limited magnitude inasmuch as the electrons are formed, in a cumulative manner and in endless number from the mercury vapor by collision between the vapor moleculesand the electrons initially generated and propelled at an ionizing velocity through the vapor. Space charge thus presents no problem in devices of this sort which employ large amounts of ionizable vapor or which other- The, efiect 4, 1928. Serial No. ceases.

, the condensed form, liquid or solid, an appreciable time periodnormally elapsesfrorn the View moment the voltage initially is applied to v the electrodes until the vapor is generated and assumes a constant pressure. Under these conditions, it has been found that even after continued operation, the pressure still tends to fluctuate quite Widelywith relatively small changes of ambient temperature andbecomes exceedingly difiicult to regulate. The

vapor pressure is a critical but important factor in a tube of this'type and mustbe con-' fined to rathernarrow limits because toohigh a pressure causes arc-back or reverse current flowg-on the other hand, when the pressure is too low, the voltage drop increases, produc ing a relatively high ion velocity which causes disintegration of I the cathode material and other deleterious effects. during the transportation and operation of a tube 01": this sort,extreme care must be exer cisedto prevent the mercury or other liquid material from splashing around within the envelope thereby giving trouble from short circuits.

We have discovered in accordance with our invention, that ifthejmercury or other spacecharge-reducing'body be spread or distributed over the-surface or surfaces of one or the facility with which thepressure thereafter is maintained, are considerably, en-

hanced. In view of the fact that in the preferred embodiment there isno vapor-produc- Moreover,-

set

ingsubstance' in liquid form present in the envelope, it is evident that the improved tube maybe operated or transported in any position without subsequent danger of electrical failure. Among the objects of the present invention are'z-to provide an electron dischargedevice in whichjthe pressure of the spacecharge-reducing vapor is quickly attained and is accurately controllable within relatively narrow limits; to provide a tube in which the condensed vapor takes on the form of a solid, rather than liquid, and in general, to improve the manufacture, construction and mode of operation of electrical trans-- lators of this character.

The drawing shows the application of our invention to a two-electrode rectifier comprising an. elongated container which is highly evacuated prior to the introduction of the vapor-producing substance, preferably mercury, and in which numeral 1 designates a cylindrical anode closed at the bottom but open at the top and made of ainetal, such as copper, which readily formsan amalgam. The anode material may also consist of solid silver, silver-plate, copper-plate or any metal upon which can be formed a desirable coat, condensate, amalgam or an alloyed surface with the group of materials referred to hereinafter as representative of the substances of which mercury is typical and from which the space-charge-reducing vapor may be.derived. The anode is exteriorly arranged to facilitate cooling thereby to maintain the temperature and pressure of the vapor eithen by an air blast or water contained in a jacket or other suitable fluid having a circulation, heat radiation or heat conservation which may be regulated closely to control the anode temperature. The container is completed by a cylindrical'top portion Qordinarily of Pyrex glass and having the lower end sealed to the anode. For eifectuating a thorough seal between the glass and metal surfaces, the upper end of the anode cylinder is flared outwardly and the material tapered down to a relatively sharp edge which is encased, by fusing, into the lower end portion of the glass envelope drawn down to the same angle to coincide with the flared portion ofthe anode in the well-understood manner. For a source of electrons, there is provided a .member 3 of anysuitable design, for example, filamentary; this member also serves as a cathode. Two J-shaped strands are connected in series, to form the cathode, structure, the latter being conveniently supported from a three-rodframework a of which the two outer rods serve as leading-in conductors. In order to protect the anode seal from excessive heat radiated by the electron source and other parts and from deleterious electrostatic eifects, there is provided a metallic cone-shaped shield 5 having a rolled or turned-in upper edge. The shield is centrally aligned of the envelope and held within the anode by friction or indentation. The anode conductor conveniently may be taken from the temperature-controlling-fluid acket. It is well-known that the maximum current obtainable in a tube of this character without the use of an ionizing vapor is limitcd by space charge, i. e., the electronimpedsmall quantity of vapor, such as mercury,

from which sufiicient vapor may be derived to neutralize the restr1ct1ve negative charges referred to hereinbefore. When 1ntroduced into the envelope in the. manner employed by prior investigators for the purpose stated, the mercury ordinarily collects as a small condensed globule or pool at the bottom of the container. Under operating conditions, the derivation of the desired amount of vapor from the globule is comparatively slow due to the small heat absorbing surface involved and even after sufficient vapor is produced, its pressure may vacillate materially under relatively small changes of temperature because the source of heat which maintains the pressure is more or less localized. The slow "formation of the vapor and the non-uniform character of its pressure under the conditions stated, produce undesirable effects from the standpoint of space charge phenomena in all forms of electron discharge devices but particularly so, in high-power, high-voltage apparatus. Moreover, when the mercury is admitted directly to the envelope in. its condensed form, there is also the possibility of including impurities which render the characteristics of the tube non-uniform.

In accordance with the present invention, we propose to condition and position the mercury or other condensate within the tube in such a manner that its effective heat absorption area is considerably greater than that of a globule of the same mercury content, thereby facilitating the production of ion-producing vapor, also such that a heat radiating surface is provided sufficiently large to maintain the vapor at relatively constant predetermined pressure. As additional features, we introduce the mercury into the active region of the electrodes in a manner which will insure an extremely pure state of the'material and which will result in its being present only in a non-liquid form. The member from which the ion-producing vapor is derived preferably takes the form ofan amalgamated or an alloyed surface formed the same diameter as theglass arm and also a sharpridge extending along the bottom Lil surface, the purpose of each of which will be explained hereinafter. In manufacture, the flange member preferably consists of an extension of the side arm and is formed by cutting an aperture in the top side of the receptacle 7 of a size corresponding to the external diameter of the side tube, then sliding the receptacle 7 over the tube a distance sufiicient to form the flange, and fusing together the receptacle and the tube after the mercury or other vapor-producing substance has been introduced. l/Vhile the mercury may be conducted directly to the receptacle 7 as a liquid, for example, by running it through the tube 6 before the latter is affixed to the envelope 2, we prefer to introduce the material in the form of a closed glass capsule 9 which may be held in an upright position by the flange-8, while the member 7 is being sealed to the side arm. The capsule prior to its insertion into the receptacle 7 is filled with mercury by a distillation process to ensure pure material. After being placed in the position shown and the side tube sealed to the envelope 2 which may be thoroughly evacuated in the well-understood manner, the entire envelope structure is given one or two shakes of sufiicient intensity to cause the capsule to strike against the sharp ridge in the bottom of the receptacle and allow themercury to escape. The mercury released in this manner is then heated either by the operating currents of the device or more quickly, if desired, by an external source of heat whereby the vapor 'distils through the tube 6. into the main envelope. In any case, the distillation process should not be carried out too rapidly as this tends to form an incomplete amalgamation, indeed, if there is available suflicient time, the heat derived by reason of ambient room temperature is particularly effective in forming a uniform coat or alloy. The vapor thus procured condenses and amalgamates with the interior surface ofthe anode which is maintained at the proper temperature for this purpose by the circulatory cooling fluid in case the tube is operating, whereby a thin layer of mercury distributed over said surface is produced. After the anode has been thoroughly amalgamated the side tube 6 mayor may not be sealed ofi from the envelope, as desired. By firstutilizing a quantity of distilled mercury contained in the capsule and then later re-distilling the material into the envelope, a double distillation process, a very pure conditions'of the mercury surface is assured. It is to be noted that the second distillation step is dfi".

liberately provided for by forming the tube 6 with an approximate right-angle bend which together with trap member 7 precludes accidental movement of the liquid into the main envelope by gravity in which case the amalgamation would be only partially complete and the liquid if in excess, would enpresent application.

vention provided there is present an amal-,

gamated surface having area large enough to provide sufficient vapor for effectively reducing space-charge. 7

On test, a rectifier such as described, consistently shows a constant operating characteristic and there is sufficient amalgam present to furnsh vapor fora long tube operating-life, It is evident that the liquid 1nercury in the reservoir 7 is always available to renew the amalgam, if desired, although we have found that further distillation is not necessary even after long continued operation, hence, the side tube 6 normally is sealedoff. The vapor may be formed readily within the device upon application of suitable voltage because the amalgamated surface upon which the heat and electrostatic field act is large, hence, the tube attains its normal operating characteristics almost immediate ly. If desired, the anode temperature may be controlled independently of the tube operation, for example, by heating or cooling the circulatoryfiuidso that the proper vapor pressure is available at the same instant that the operating potential is applied.- It is found that the vapor pressure remains at a desirable value, accurately controllable, by

regulating the anode temperaturein the manner stated. The desirable anode temperature may vary over a considerable range dependdevices, i. e., those in which thecurrentis car- IlfiECl principally by electrons and which employ a plurality of elements including an electron emittingsource and a substance in the form of vapor to reduce space charge or to offset other deleteriousaction. It has special adaptation to high-voltage, high-pow ered electric discharge apparatus, for example rectifiers, also to devices of the thyratron type so-called which utilize an electrostatic control member for controlling a. dis-' charge of arc-like character as described'and claimed in application Serial 'No.-' 268,975, filed April 10, 1928, in thename of 'A.-W.' Hull and assigned tothe same-assignee as the- VVhile we have described our invention with particular reference'tomercury as the condensate or the vapor-producing component of the alloy, it is evident that other materials 'may be employed to advantage, for

example,suitable alkali metals such as caesium and rubidium, the vapor pressure of which is sufiiciently high at operating temperatures and which are capable of forming a condensate or alloy. It is also feasible to employ iodine for the purposes stated which may be applied to the interior surface of the anode by painting or in any other suitable manner. The present invention therefore contemplates the use of any substance, liquid and solid, which, at readily attainable temperatures, supplies vapor in quantity sufiicient to eradicate space charge and which is capable of adhering to a member in the device to form a vapor-yielding surface, said member responding quickly and accurately to temperature control. It is obviously necessary. to choose the metal of the anode or of other member upon which the active surface'is formed with the specific'vapor-producing material in mind so that an eifective surface be produced. In the event that materialsare employed which will give the desired vapor pressure only at temperatures in excess of the temperature which glass portion 2 normally attains during operation, it may be necessary to maintain this portion of the container at a temperature higher than the said temperatures, for example, by means of a heat-absorbing enclosure (not shown) in or der to ensure'that the condensation of the vapor-producing substance takes place at a rial from which to derive the space-chargereducing vapor; V i

From the foregoing, it is evident that the invention is not limited to rectifiers or twoelectrode devices such as has been shown for the sake of illustrating the principles involved, but maybe applied to all forms of electrical discharge apparatus, amplifiers, oscillators and the like wherein space current is carried in the absence of cumulative or substantial ionization. Accordingly, we de-.

cure by Letters Patent ofthe United States, i

1. A thermionic device comprising a filamentary cathode and a cooperating anode bet-ween which the discharge tends to be limited by space charge, said anode being 7 adapted to have its temperature controlled,

and means, comprising a substance forming a substantial coating on said anode, for reducing space charge. I

2. A thermionic device comprising an evacuated envelope containing an electron emitting cathode and' a cooperating anode in heat-receiving relation therewith whose temperature is adapted to be varied, means for reducing the space-charge which limits the current flow between the electrodes, said means comprising a vapor-generating substance spread over the surface of said anode whereby the rate of generation of the vapor may be regulated to maintain a substantially constant space-charge-reducing effect.

3. A thermionic device comprising a plurality of electrodes between which the dis charge tends to be limited by space-charge, means for'varying the operating temperature of one of said electrodes and means for minimizing the space-charge, said last men tioned means comprising a condensable vapor, the pressure of which is maintained at a predetermined value by the temperature of the electrode adapted to be varied.

4. A thermionic device comprising a plurality of electrodes between which the discharge tencs to be limited by space-charge effect, means for substantially neutralizing the space charge, said means comprising a coat of space-charge-reducing material on one of said electrodes, and means for vaporizing and maintaining substantially constant the vapor pressure of said material, said lastmentioned means including a device for varying the temperature of the said one electrode.

5. In the art of operating a thermionic device comprising-an evacuated envelope, cooperating electrodes therein including a source of electrons, one of said electrodes being amalgamated, the method which consists in varying-the temperature of the electrode to maintain a sufiicient quantity of mercury vapor in the device to reducespace charge efect;

6. A thermionic device comprising an electrode having an amalgamated surface, the temperature of-which is adapted to be varied within a temperature range including the temperature necessary to produce a mercury vapor in quantity sufiicient for reducing space charge to a desired extent and means for maintaining said surface at such vapor-producing temperature.

7. A thermionic device comprising a plurality of electrodes between which the discharge tends to be limited by space-charge,

anode having an amalgamated surface in por is evolved from the anode surface and its pressure maintained at a desired value.

10. A thermionic device comprising an electron emitting cathode and a cooperating anode between which space current is carried principally by electrons, means for reducing space charge, said means comprising a source of vapor distributed over a surface in the device, the temperature of said surface being adapted to be varied, said means comprising an amalgam on the anode.

11. A thermionic device comprising the combination of an evacuated envelope containing a cathode adapted to emit electrons and cooperating electrodes between which current is carried principally by electrons, a source of ion-producing vapor associated with said envelope for reducing space charge, the material of one of said electrodes other than the cathode being such as to allow the formation of a condensate derived from said vapor under operating conditions, said electrode being adapted to have its temperature varied.

12. A thermionic device comprising the combnation'of an evacuated envelope hav ing an exterior portion formed of a. metal comprising copper and constituting an electrode, said envelope containing a cathode adapted to emit and to propagate electrons toward said electrode, a source of mercuryyielding material associated with said envelope and forming gamated surface.

13. A thermionic device comprising an envelope containing an electron emitting cathode and a cooperating element provided with an amalgamated surface, temperature-varying means for causing thealternate release of the mercury from said surface and the condensation of the released mercury on the surface.

14. A thermionic device comprising an envelope contalnmg an electron emlttlng cathode and a cooperating element provided 'Wltll an amalgamated surface, means for varying the temperature of said surface whereby the mercury is alternately evolved and condensed on said surface.

15. A thermionic device comprising an envelope containing an electron emitting cathode and a cooperating element provided with an amalgamated surface, temperature-vary ing means for releasing the mercury from with the copper, an amal said surface and for maintaining the pressure of saldvapor at a deslred value.

In witness whereof, MARCUS A. AOHESON has hereunto set his hand this 23rd day of August, 1928, and J AMEs'L. ZEHNER has hereunto set his hand this 29th day of August,

MARCUS A. ACHESON. JAMES L. ZEHNER.

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