US2081714A - Electron discharge device - Google Patents

Description

May 25, 1937. RQTHE ET AL 2,081,714

ELECTRON DISCHARGE DEVICE Filed April 25, 1954 INVENTORS HORST ROTH E WERNER KLEEN ATTO RN EY Patented May 25, 1937 iJNlTE STATES T ones ELECTRON DISCHARGE DEVICE rnany, a corporation Application April 25,

of Germany I 1934, Serial No. 722,223

In Germany May 1'7, 1933 4 Claims.

Our invention relates to hot cathode gas rectifiers which are used to'change alternating current into direct current. In order that a maximum efficiency may be secured it is necessary 5 that the rectifier should present as high as possible a resistancein one direction and as low as possible a resistance in the opposite direction.

While the high-vacuum hot cathode rectifiers known in the prior art have a practically infinitely high resistance in the non-conductive direction, their resistance in the so-called conductive direction is also quite high. The voltage required to produce a certain current by neutralizing the electronic space charge about the heated cathode, according to the well known space charge law, is less, the smaller the distance between cathode and anode, and the larger the surface area ofv the cathode. However, for constructional reasons it is not feasible to make the intervening distance between the cathode and the anode so small or to make the surface of the cathode so large, that the internal resistance in the conductive direction will become sufficiently low.

In order to diminish this internal resistance the rectifier tubes are frequently filled with a vapor or gas atmosphere. With such a rectifier, as soon as the plate potential is sufiiciently high, the electrons are able to ionize the molecules of this vapor or gas atmosphere. The resulting positive ions move toward the cathode and traverse the electronic space charge around the cathode, thereby releasing a large number of electrons. Thus, for instance, one mercury ion will set free from 100 to 200 electrons from the space charge.

These ions, however, occasion a very troublesome secondary action. Because of their great mass, they have very low speeds, particularly at their points of origination in the neighborhood of the anode. As soon as the current flowing thru the rectifier exceeds a certain value, there appears in front of the anode an ionic space charge which becomes correspondingly denser, and extends correspondingly farther toward the cathode, as the current strength becomes greater. With increasing current strength therefore, the ionic space charge drifts to the cathode, and causes an increase in the field intensity about the cathode, but primarily as a result of the change in the voltage gradient along the discharge path between anode and cathode there is an enlargement of the space within which ionization is possible. Primarily because of this increase in possibility of ionization with increasing current strength, such gas filled tubes have a discharge characteristic similar to that of an arc; that is, portions with a negative internal resistance are found. If such tubes are used in rectifier apparatus, the associated circuits and control elements may be caused to oscillate when used in receiving circuitsfor radio installations, recourse must be had to expensive and complicated ways and means to prevent trouble.

According to our invention this negative resistance part 'of the discharge characteristic is avoided by means of an electrode construction based upon the following considerations.

The purpose of. the gas or vapor atmosphere is to supply, by means of impact of the electrons or gas molecules, enough positive ions to release from the electronic space charge the required number of electrons. The gas pressure and the space in which ionization is possible must, therefore, be chosen so large that the fall of potential occurring in the rectifier tube during the conductive phase is sufficient to produce the re quired number of ions. On the other hand, it is necessary to prevent the resulting ionic space charge from causing any essential increase either in ionization or in the field intensity around the cathode. How this purpose is attained will be explained by v a number of practical examples which, however, are not intended to imply any limitation.

The novel features which we believe to be characteristic of our invention are set forth with 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:

Figure 1 is a diagrammatic representation of a section taken transversely to the longitudinal axis of a rectifier tube embodying our invention; and Figures 2, 3 and 4 are diagrammatic representations of a similar section taken of modifications of the tube shown in Figure 1.

Referring to Figure l the cathode a, preferably of the indirectly heated or unipotential type, is surrounded by a mesh electrode b and a solid or even apertured electrode 0. The two electrodes 1) and c are at the same potential and directly interconnected; for example, by the wire 11. These electrodes are mounted in a sealed envelope which contains gas at the proper pressure. Now, if the potential drop between the cathode a and the two electrodes 1) and c is greater than the ionizing voltage of the gas in the envelope e, then the electrons will be able to ionize the gas molecules. This ionization will occur primarily between electrodes b and c, for inside this space the electrons in this case have a velocity which is adequate for causing ionization. If the distance between a. and b is made smaller than the distance between I) and c then it occurs that the major portion of the ionization will take place between b and 0. Since the cathode a has a certain pull thru the mesh or apertured electrode b, there will exist a certain potential gradient in the space between D and c which will convey ions towards the cathode, altho a certain number will bev collected by the electrode 17. In the space between D and 0 there will doubtless be at higher current strengths an ionic space charge also, but if b is made of appropriate dimensions, this will no longer cause any pronounced change in the ionization. By providing the proper intervening space between a and b any ionic space charge which may form between a and b can be made svmciently small to be negligible, and thus have little effect on the field intensity at the cathode.

Rectifiers that have been built in accordance with this principle, possess a current-voltage characteristic having no signs of negative resistance or only slight traces of the negative resistance characteristic.

Of course, the above construction may be changed and modified extensively and still obtain the desired characteristics. Figure 2, for example, shows a simpler construction in which each of the two electrodes 17 and c consist of two parts which are welded together. 7

Figure 3 shows another modification of our invention. In this case the electrode b is replaced by four electrodes f in the form of fins or ribs which are disposed on the electrode 0. These ribs produce the same effect if they are not in the longitudinal axis of the cathode, but lie in a plane transverse to this axis.

Figure 4 shows an anode g of star-like crosssection which is directly derivable from the construction shown in Figure 3.

All of the above forms of electrodes have the same purpose. They provide that there is sufficient space available in which ionization can take place without the resultant ionic space charge exerting such a marked influence upon ionization and the field strength at the cathode that there are portions of the discharge characteristics which have negative resistance.

In high-vacuum discharge tubes electrodes of somewhat similar shape operate in a different way and serve wholly difierent purposes; as, for example, to obtain a high saturation voltage and an adequately large radiation surface for the dissipated energy, or for the suppression of secondary electron emission. However, from the preceding description it is obvious that between such high vacuum tubes and the gas filled rectifier tubes here disclosed there are fundamental differences.

-While we have indicated the preferred embodiments of our invention of which we are now aware and have also indicated only one specific application for which our invention may be employed, it will be apparent that our 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 our invention as set forth in the appended claims.

What is claimed to be new is:

1. A hot cathode gas filled rectifier tube having a straight cathode, a tubular mesh electrode surrounding and concentric with said cathode and a second tubular electrode surrounding and concentric with said cathode and the mesh electrode, said mesh electrode and said second electrode being directly electrically connected.

2. A hot cathode gas filled rectifier tube having a straight cathode, a tubular eleo-trode'surrounding and concentric with said cathode and a second tubular electrode positioned between the cathode and the electrode surrounding and concentric with said cathode, said second tubular electrode being of mesh material, said tubular electrodes being directly electrically connected together to be at substantially the same potential.

3. A hot cathode gas filled rectifier tube having a straight cathode, a tubular anode surrounding said cathode, a tubular electrode of mesh material positioned between said cathode and said anode and directly electrically connected to said anode to be at substantially the same potential.

4. A hot cathode gas filled rectifier tube having a .straight cathode, a tubular mesh electrode surrounding and concentric with said cathode and a second tubular electrode surrounding and concentric with said mesh electrode, said mesh electrode and said second electrode being directly electrically connected, the spacing between said cathode and said tubular mesh electrode being less than the spacing between said tubular mesh electrode and said second tubular electrode.

HORST ROTH'E. WERNER KLEEN.

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