US2171215A - Gaseous discharge tube - Google Patents

Description

Aug. 29, 1939. A. KAUFFELDT GASEOUS DISCHARGE TUBE Filed June 1 2, 1937 POTFNT/Al kbnSQ INVENTOR ALFONS KAUFFELDT ATTORNEY Patented Aug. 29, 1939 PATENT oFFIcE GASEOUS DISCHARGE TUBE Alfons Kauffeldt, Berlin, Germany, assignor to Telefunken Gesellschaft fiir Drahtlose Telegraphic in. b. H., Berlin, Germany, a corporation of Germany Application June 12,

1937, Serial No. 147,852

In Germany July 4, 1936 4 Claims.

My invention relates to electron dischargedevices, more particularly to improvements in such devices of the gaseous discharge type.

The invention is concerned with tubes possessing a so-called drooping characteristic, for instance, tubes operating with a gas atmosphere or filling. The difiiculty residing in the control of gaseous tubes is due to the fact that electrodes operated with a negative biasing potential are at once surrounded with a neutralizing positive space charge so that, even at extremely small distances from the electrode, control action is entirely precluded.

This difficulty has in the past been circumvented by disposing the electrodes at such close proximity to one another that their mutual distance was less than the mean free path of the electrons, thereby precluding all changes of any appreciable ionization taking place in the intervening space. While it is true that this affords a means to control large currents, the efiiciency of tubes of this kind is not particularly high.

The object of my invention is to provide an electron discharge device of the gaseous type having improved characteristics and a circuit therefor.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims, but the invention itself willbest be understood by reference to the following description taken in connection with the accompanying, drawing in which Figure l is a diagram illustrating the fundamentals of my invention, Figure 2 is a schematic diagram of a circuit employing my invention, and Figure 3 is a schematic diagram of an electron discharge device in section embodying my invention and a circuit therefor.

Now, the present invention is predicated upon the idea that every'gas discharge is controllable by its plate potential. Of course, directly applied, such a control would serve no practical purpose at all for it would lack amplification. But thecontrol action following is feasible, that is connecting in parallel relation to a gas or glow tube, a device the resistance or current conductivity of which maybe controlled in some suitable way without consumption of power. In the presence of a definite resistance of the par allel connecteddevice a summational characteristic for both devices is obtained by adding, for the same potential, the corresponding currents. Hence, for difierent resistances there results a family of curves or characteristics, and

this family of curves comprises a controllable range.

The principle of my invention follows from a study of Figures 1 and 2 of the attached drawing. Referring to Figure 1, Gdenotes the schematic characteristic of a glow discharge, while P is a family of characteristics of the parallel connected device. As regards the latter, devices possessing such characteristics are known in the prior art, and the various graphs are obtainable in the absence of energy dissipation, G+P is the family of summational curves resulting from a parallel connection of the two devices.

It is known in the art that a glow discharge is stabilizable by the aid of a series resistance, the latter having, however, to be so proportioned that its characteristic will intersect the glow discharge characteristic at only one point if plotted as a function of E-U, where E is a constant D. C. voltage of suitable value, and U the potential prevailing across the resistance. It can be readily seen from Figure 1, that according to the choice of the parallel resistance P, the discharge is stabilized at another potential, namely at a. voltage for which the load line W will intersect the corresponding summational characteristic G+P. Upon the whole there results an operable range marked by J1 U1 and J2 U2.

No special assumption has been made in regard to the parallel device P, But the same may consist either of a high vacuum tube or else it may consist of a controllable gas discharge. The output resistance W (Figure 2), for instance, could consist of the primary winding of an output transformer. I

Now, according to this invention the two devices P and G are united into one discharge system in such a way that in a gas or vapor filled vessel (B) a non-aperturedanode A and an apertured cathode Kare fitted into a frame J made of a suitable insulation material in such a way that between them a confined or closed space results, and that the mutual distance between them is less than the mean free path of the electrons. Between anode and cathode, finally, is a control electrode S which is also apertured and which, inside the space, mutually covers the two first named electrodes. The cathode is preferably coated.

If by way of a useful resistance W a suitable n im E b a ie "to the two Out electrodes, a glow discharge about the insulation frame may be struck and maintained between the outer surfaces of the cathode and the anode since these surfaces are separated a distance greater than substances. as to insure a biasing tension, in other words, the

the mean free path of an electron in the gas within the envelope. Evidently, in this instance, however, an electronic discharge also occurs from the cathode to the anode across the inner space. At the cathode, as a result of impacts of the positive ions from the negative glow discharge,

electrons are produced, and inasmuch as the field intensity prevailing in the inner space exceeds that in the outer space (as a result of prevailing distances), part of the electrons originating at the cathode will be directly withdrawn to the plate. Referred to the main discharge about the insulation part J, this electronic discharge, therefore, represents a shunt just as in Figure 2. The current flow (transmissibility) of this shunt is regulable by control grid S so that exactly the case of Figure 2 results. Under certain circumstances it may be preferable to dispose anteriorly of the control grid a screen grid which is operated on a suitable positive bias in order to preclude from the control grid such positive ions as happen to fly through the cathode apertures.

It will be seen from Figure 1 that the efficiency will be greater the smaller the current flowing through the parallel resistance P. If the resistance line characteristic W is made steeper, the range of current which can be controlled becomes greater.

In lieu of a cold cathode K shown in Figure 3, it would, of course be feasible also to use a thermionic type of cathode. The incandescing thereof may be direct or indirect, and the same may be coated with emissive oxide. Moreover, this cathode could be either apertured, say, in the form of a grid, or it could be impermeable, i. e., nonapertured (or solid). Further, only one side or face of the cathode could be coated with oxide, and the heat dissipated on the cathode as a result of the main discharge could be used for heating.

Inasmuch as the summational characteristic of the arrangement is of a drooping nature, circuit arrangements can be assembled which are predicated for their operation upon a device with a drooping characteristic, above all, for de-attennation (regeneration) of an oscillation circuit or the production of oscillations.

The material from which frame J may be made consists preferably of low-loss refractory ceramic The frame properis so constructed frame imparts to the electrodes at least in one direction of their surfaces a mechanical tension with a view to'keeping them taut.

While I have indicated the preferred embodiments 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 limitedto 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.

I claim:

1. An electron discharge device including an envelope having a gaseous atmosphere, electrodes within said envelope having surfaces spaced from each other less than the mean free path of an electron in said gaseous atmosphere, and a control element positioned between said surfaces, in-

sulating means for supporting said electrodes and control element in spaced relationship, said surfaces and said insulating supporting means enclosing a space in which a gaseous discharge cannot take place, said electrodes having surfaces outside of said enclosed space exposed to the gaseous atmosphere within the envelope and spaced apart a distance greater than the mean free path of an electron in the gas for providing an ionizable path between the electrodes on the outside of said space whereby a gaseous discharge may take place between the outside surfaces of said electrodes.

2. An electron discharge device including an envelope having a gaseous atmosphere, electrodes of sheet material each having a surface spaced from the surface of the other electrode less than the mean free path of an electron in the gaseous atmosphere and a control member positioned between saidsurfaces, insulating meansfor supporting said electrodes and control member in spaced relationship, said surfaces and said insulating means enclosing a space in which a gaseous discharge cannot take place under operating conditions, the other surfaces of said electrodes being exposed to the gaseous atmosphere within the envelope, said other surfaces being spaced apart a distance greater than the mean free path of an electron in the gaseous atmosphere whereby a gaseous discharge can take place between the other surfaces of said electrodes.

3. An electron discharge device including an envelope having a gaseous atmosphere, a plurality of fiat electrodes having surfaces spaced from each other less than the mean free path of an electron in said gaseous atmosphere, a control grid positioned between said surfaces, insulating means for supporting said electrodes and said control grid in spaced relationship and providing with said surfaces an enclosed space in which a gaseous discharge cannot take place during normal operation of the device, the surfaces of said electrodes outside the enclosed space being exposed to the gaseous atmosphere within the envelope and spaced a distance greater than the mean free path of an electron in the gaseous atmosphere whereby a gaseous discharge may take place between the surfaces of said electrodes outside the enclosed space.

4. An electron discharge device including an envelope having a gaseous atmospher.e, a plu-v rality of fiat electrodes having surfaces spaced from each other less than the mean free path of an electron in said gaseous atmosphere, a control grid positioned between said surfaces, insulating means for supporting said electrodes and said control grid in spaced relationship and providing with said surfaces an enclosed spacein which a gaseous discharge cannot take place during normal operation of the device, the surfaces of said electrodes outside said enclosed space being exposed to the gaseous atmosphere within the envelope and spaced a distance greater than the mean free path of an electron in the gaseous atmosphere whereby a gaseous discharge may take place between the surfaces of said electrodes outside the enclosed space, one of said flat electrodes being an anode and the other of said electrodes being a perforated cathode.

ALFONS KAUFFELDT.

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