US2075208A - Electron discharge device - Google Patents

Description

March 30, 1937. o. KRENZIEN ELECTRON DISCHARGE DEVICE Filed July 19, 1935 INVENTOR` OTTO KRENZIEN ATTORNEY.

Patented Mar. 30, 1937 UNITED STATES ELCTRON DISCHARGE DEVICE Application July 19,

1935, Serial No. 32,200

In Germany December 22, 1933 4 Claims.

My invention relates to electron discharge devices, more particularly to improvements in electron discharge devices of the gas or vapor type.

One of the most difcult problems in the manu- 5 facture of electron discharge tubes having a gas or vapor atmosphere, especially tubes designed for relatively high voltages, is in the prevention of back-arcing, that is to say, the initiation of a discharge during the blocking or non-conducting phase. Various ways and means have been suggested to prevent back-arcing, but up to the present no really satisfactory method has been deglilsed, especially where high voltages are dealt w1 Use has been made of conducting and nonconducting screens or grids interposed between the discharge of electrodes to prevent such backarcing or to at least cut down the intensity of such arcing. The anodes (which, in the case of back-flashing or back-arcing, operate as the cathodes) have also been positioned within eX- tensions or arms of the tube envelope or disposed within shields which minimize the strength of the current likely to flow thru the arc discharge once the latter has been initiated in a reverse direction because the shields cause a restricted discharge. All of these Ways and means and others of a similar nature, however, are found to fail when the potentials to be blocked are greater than, for example, 15 to 20 kv. Backarcing with these potentials is preventable only when the initial or breakdown voltage of the gaseous discharge is increased beyond the value to be blocked or prevented in a safe and dependable manner. It is well known that the breakdown voltage of unassisted gas discharges is a function of the quantity of gas or vapor conned between the electrodes, i. e., a function of the product of inter-electrode distance and the prevailing gas pressure. It is likewise known that below a critical point of this product with decreasing values, the ignition or breakdown potentialrises very suddenly or steeply. It is diicult if not impossible to secure Values of any desired small amount for this critical product by choosing a desired low pressure for the gas lling inasmuch as gases or unsaturated vapors, at unduly low filling pressures become occluded, in the course of a few working hours, in the walls of the discharge vessel or in the electrodes.

Hence, it is necessary to choose as small as feasible a distance between the electrodes in question. However, this step involves the di'iculty that when the distance is unduly small between the electrodes between which a discharge takes place, the iiashing or arcing voltage of the discharge attains inacceptably large magnitudes in the desired or working direction. (Socalled impeded discharge.)

It is an object of my invention to provide an improved type of electron discharge device of the gas or vapor type intended for use as a rectier in which breakdown in a reverse direction during the non-conducting phase will be practically eliminated.

According to my invention, the electron discharge device is provided with an envelope having a gas or vaporcontent and enclosing an anode,V and a'cathode providing the main electron source, the cathode and the anode being so disposed and constructed that the discharge path of the electrons fromthe cathode to the anode in the working direction during the conducting phase is several times longer than the paths of the electrons released at the anode in the blocking or non-conducting phase from the anode to the cathode.

In this connection care'must be taken so that the possible paths of such secondary electrons as may have been released at the plate during the blocking phase are so small or short that the flashing or arcing potential of a gaseous discharge in the blocking phase will be above the maximum voltage liable to occur in operation; in other words, that the product of gas pressure and distance inside the discharge vessel, wherein an. electric field is set up during the blocking phase, will be kept as small as feasible.

To do this` the lines of force of the field during the blocking phase should not differ in length from each other by more than a factor of 3. In order that this condition may be insured it is necessary that such lines of force as issue from the posterior face of the plate, from the lateral surfaces or the supporting elements thereof are suppressed by suitable means such as shields or the like, that is the tendency of discharges along these lines of force should be suppressed while at the same time insuring that the cathodic parts of the discharge vessel are so shaped that lines of force along which discharges are possible will terminate only in a plane parallel to the front face of the anode. The distribution of the lines of force inside the electron discharge device during the blocking or non-conducting phase can be determined by the application of well-known electrostatic laws and methods, while during the conductive phase, once ionization of the gases has been initiated, the situation will be found to be totally different since then space-charges of positive ions cause Y an essential change in the distribution of the eld.

The novel features which I believe to be characteristic of my invention are set forthwith particularity in the appended claims, but the invention itself will best be understood by reference to the following description taken in connection with the accompanying drawing in which H Figure 1 is a diagrammatic verticalV section ofV an electron `discharge device embodying my invention; Figure 2 is a View with parts in section of an electron kdischarge device *embodyingV my in vention; and Figure 3 is aV vertical section of a modication of the anode and shield of the electron discharge device shown in Figure 2.

In Figure 1, cathode I supports an element or..

shield 2 which may be dish-shaped and is disposed at a small distance opposite the front face 3 of the plate 4. The anode or plate 4 as well as its supply lead 5 are surrounded by a shield 6. The -latter may be metal in which case it must :be either insulated or be kept 'at cathodeV portential or substantially so. Ineither case, it is necessary that the distance between anode 4 andits lead 5, on the'one hand, andthe shield 6, Yon the other hand, be such that no dischargeis likely to take place in the interstitial spaces regardless of whether this'discharge 'is brought about by a potential diiference between the' anode` and the shield or by the discharge between anode and cathode.

Referring to the schematic view Figure l,'

front surface of the anodeY and the dish partof the cathode. Along the lines of force which issue from the lateral surfaces of the anode or from the supporting elements thereof (and `which arernot indicated in the drawing) discharges are not likely because of the Ysnug fitting or. VVsurrounding of the shield -6, While nolines of force Y are established Awhich begin at the frontsurface of` the' anodeand terminate at that surface. of

the cathodefwhich is on the opposite side of the` cathode from the anode and on the supporting Velements therefore. The result is that, at the operating pressures andat the predetermined distances between the electrodes and unassisted gas discharge duringv the blocking phase cannot take place. Hence, not` only the distance between the anode andthe anode screen is 'imi Y portant, but the proper dimensionV ofthe `diameter of the planar part of the cathode turned towards the anode comparedwith thelength of the other structural parts of the cathodegand their cross sectional diameter must be selected -so that under no conditions will stray lines of force starting at the front surface of the anode terminate at parts of the cathodic structureother thanY the 'cathode surface opposite the anode frontal surface.

VIn Figure 2, the envelope i of lthe electron discharge device is provided with two presses 8 and 9, the press 8 supporting the anode, with its sible;

be placed either so close to the lead I6 that no shielding means, while press 9 carries the cathode structure. The anode consists ofY a support-` ing element I0, the anode body with frontal surface II, and a shield I2.

loop-shaped heated cathode I5 as well as the cathode dish I6. 4 issues from the cathode I5; hence, in the transmitting phase the electrons` travel from the cathode I5 to the anterior surface of the anode V.I I, while in the reverse phase or yblocking phase such electrons as may be released on II ,will have available for their travel only the short'path be tWeennII and I6 for ionization. e

In Figure 3 is shown the details of construction of the anode including the' shield. On the The press 9 supports Y two supporting wires VI3 and I4 which carryV the The thermal electron emissionA support wire Iltis secured the anodeor plate Y body I1, having the anterior surface II. A shield I2 preferably of metal is carried by the insulat#V ing tube I8.

The distance` between the shield I2 and the plate body at -the points marked a and b is so small Vthatno unassisted dischargeis pos- The cylindrical portion of the shield may discharges can take place or else as shown in the iigure, diaphragms I9, 2li', 2I, may be provided by means of which Ythe space Aformed between the anode lead I0 and the interior of the Yshield is subdivided so that inthese subdivisions no discharges can occur. The shield I2as well as the diaphragms or baiiles I9,2I) and 2| may be made,

either of insulating material or` else of some con'- ducting material. be desirable to apply to it the cathode potential. When this shield has a potential which is equal or close to thatof the cathode, it is very impor- If the shield'is metalit may' tant to make the distances between the anode or l anode lead, on the one hand, andthe shield, on1

the other hand, such that nounasrsisted discharge canrbe initiated, By impressing proper voltages upon the anode shield, the shield'canbe used for control purposes.y It may be advantageous in this connection to cover the lower open front surface of the anode screen or shield by a gridor grate-like structure which would thus be placed outside of the frontal surface of` the cathode; action of the anode screen couldV be combined with the control action of some other Y-part of i the tube.

The distance between the Vfront surface ofV the anode and the surface of the cathode'turned towards it is limited bythe fieldintensltyron the surface `of the anode which when the electrodes are very close may cause a marked auto-electronic' discharge which `may occasion van undesired breakdown or discharge; Y n Y While the preferred construction of the cathode is shown in Figure 2, it-may be madeV so that the entiredish portion I6 acts asrgthe heated cathode.

In this case the electron emission should occurv only from the face turned away from ythe frontal surface of the anode. 'Ihe electron emisslve coating may be of any conventional kind. 'Ihe cath- Vode may be a directly or `an indirectly heated type,

and it may be advantageous to provide heat insulating means aswell known in the art. It is possible to use a discharge gap or path to act as a source of electrons from which the electrons can beextracted by the action of the anode field. It is also feasible to use as the electron source the Spot of an arc discharge, as well" known'in the art. y

Tubes ofthe kind hereinbefore disclosed and described may be used not only as simple non- It will be understood that the control controlled discharge vessels, but in addition to the control action hereinbefore described and obtained by the protective shield surrounding the anode, further electrodes may be employed as suggested in the art to control actions either of a continuous or an intermittent kind. For example, possible to position on the part of the dish I6 turned away from the anode (see Figure 2) a control element adapted to regulate the initiation of 10 the discharge current during the conducting phase by providing an initial auxiliary discharge. It is essential in this connection, so far as practicing the invention is concerned, that these control elements as Well as their supply leads must be so disposed that the possibility of long stray lines of force emanating in the blocking or noncon-ducting phase from the anode surface will be prevented.

The gases or vapors used to ll the discharge Vessel according to the invention may consist of saturated or unsaturated metallic vapor, e. g., mercury vapor or else of inert gases such as nitrogen, hydrogen, iodine or else rare gases or mixtures of vapors and gases.

While I have indicated the preferred embodiment of my invention of which I am now aware and have also indicated only one specific application for which my invention may be employed, it Will be apparent that my invention is by no means limited to the exact forms illustrated or the use indicated, but that many variations may be made in the particular structure used and the purpose for which it is employed Without departing from the scope of my invention as set forth in the appended claims.

What I claim as new is:-

1. An electron discharge device having an envelope containing a gaseous atmosphere, an anode having a lead-in supported within said envelope and having a surface transverse to the longitudinal axis of the envelope, a cathode oppositely disposed to said anode and having an electron emitting surface, a shield connected to the cathode and positioned between the emitting surface of said cathode and the anode and having a surface transverse to the longitudinal axis of the envelope and extending radially beyond the anode an-d cathode, whereby the discharge path of the electrons from the emitting surface of said cathode to said anode is greater than the distance between said anode and said shield, and a shield around said anode and its lead-in spaced from said anode at such a distance that no discharge will occur between the shield and the anode and its lead-in under operating conditions of voltage and gas pressure, sai-d shield being open only at the transverse surface of the anode.

2. An electron discharge device having an envelope containing a gaseous atmosphere, an anode, a lead-in for supporting said anode from one end of the envelope, a shield surrounding said lead-in and anode and having an opening for partially exposing the surface of sai-d anode, transverse metallic shields positioned within the enlarged end of said shield and spaced from each other, and provided with aligned apertures thru which the anode lead-in extends out of Contact with said shiel-ds, a cathode supported from the other end of the envelope and having a surface transverse to the longitudinal axis of said envelope, said cathode having an electron emitting portion shielded by the transverse surface from said anode.

3. An electron discharge device having an envelope containing a gaseous atmosphere, an anode supported from one end of said envelope and having a surface transverse to the longitudinal axis of the envelope, a shield surrounding said anode except at said surface whereby any discharge is confined to said surface and a cathode assembly supported from the other end of the envelope and including an imprforate surface transverse to the longitudinal axis of the envelope and an electron emitting portion disposed on the opposite side of said transverse surface from said anode, the transverse surface of the cathode extending in a radial direction beyond the outside surface of the anode whereby the path of electrons from the emitting portion of the cathode to the transverse surface of the anode is greater than the distance between the transverse surface of said anode and the transverse surface of said cathode.

4. An electron discharge device having an envelope containing a gaseous atmosphere, an anode supported from one end of said envelope and 'naving a surface transverse to the longitudinal axis of the envelope, a shield surounding said anode and having an opening adjacent the transverse surface of the anode, and a' cathode having a dish-shaped portion transverse to the longitudinal axis of the envelope and opposed to the surface of the anode, the surface of said dish-shaped portion of the catho-de opposite from said anode being coated with an electron emitting material and a heater for said cathode,

OTTO KRENZIEN.

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