US1714407A - Gaseous conduction apparatus - Google Patents

Description

May 21, 1929.

c. G. SMITH QASEOUS CONDUCTION APPARATUS Filed July 30, 1923 hatnitr QWM mm. m g xm evu Patented May 21, 1929.

UNITED STATES CHARLES G. SMITH, OIi MEDFORI); MASSACHUSETTS, ASSIGNOR, BY MESN E ASSIGN- MENTS, TQ RA'YTHEON INTI, OF CAMBRIDGE, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS.

GASEOUS CONDUCTION APPARAT'ITS.

Application filed July 30,

The present invention relates to gaseous conduction apparatus.

The principal object of this invention is to provide certain improvements in gaseous conduction tubes in order to stabilize the gas pressure within the tube and to reduce the voltage drop through the tube in operation.

It has been found thatin the usual types of gaseous discharge tubes involving the ionim zation of a gaseous medium between electrodes the discharge becomes erratic after a comparatively short time. This has been found to be principally due to the fact that various quantities of the gas are actually is absorbed by the material of which the electrodes are composed, thereby seriously affecting the characteristics of the tube and finally tending'to reduce the gas pressure below the value required for stable operation. It is believed-that this effect is brought about through the bombardment of the cathode by positive ions, which are enabled to progress a considerable distance between the molecules of the cathode material and become thus entrapped. Since the conducting property of the gaseous region takes place by virtue of the formation of positive ions from the molecules of the gas, it will be seen thatcontinued operation of the apparatus results in loss of a. considerable amount of the gas, leading to disadvantages above described.

VVith the above object in view, the principal feature of the present invention contemplates the provision of an electrode provided with a liquid surface and immersed in a gas for electrical conduction. It has been found that disappearance of the gas is very materially reduced by the use of such a liquid electrode, supposedly due to the factthat ions and molecules driven into the liquid are enabled to force. theinway back through the liquid and return to the gaseous region. Further -more,this type of device has been found to possess the distinct advantage of operating with a very low voltage drop.

Other features of the invention consist in certain novel features of construction, combinpt-ions and arrangement of parts hereinafteridcscribed and. claimed, the advantages of which will be apparent to those skilled in the art from the following description.

In the accompanying drawings Figure 1- is an elevation in section of a rectifier tube embodying the features of the present invention netic field is actin 1929;. Serial No. 654,647.

ing apparatus, the former relating to a type of gaseous conduction apparatus which depends upon the employment of a non-uniform magnetic field for operating upon the paths of electrons in the gas to obtain the rectifying action and the latter relating to the type of apparatus depending upon the formation of a spaced charge of positive ions. According to the present invention these devices are provided with a cathode having an active surface which IS in the form of a liquid under normal operating conditions. This active material must be electrically conducting and is preferably of such nature as to solidify when the tube is not in operation. Furthermore,

in order that conduction may be allowed to take place principally through gaseous ionization and conduction, it is desirable that the liquid electrode material be of such nature as not to present an excessive vapor pressure at normal operating temperatures.

The rectifying apparatus shown in Fig. l employs two electrodes separated by a distance comparable to the mean free path of electrons in the gas, conduction between the electrodes being caused to take place by the application of a magnetic field which is stronger adjacent one electrode and becomes progressively weaker toward the other. Such an apparatus will conduct only when the electrode in the region of the stronger magas cathode and will become insulating w en. the electrode in the 'weaker magnetic field is acting as cathode.

The anode 12 is made cup shaped and has a PATENT OFFICE. f

plane active surface 14. This electrode is supported within a sealed tube 10 of insulating material such as glass. The tube is provided with an annular trough 18 which is filled with the material 16 composing the liquid electrode. The material of the liquid electrode may be of any suitable conducting substance which takes the form of a liquid without excessive vapor tension under operating conditions. To this end, an alloy of sodium and potassium may be conveniently employed. In particular, one alloy of this character which solidifies at 10 below zero approximately, and boils at a temperature near 700 C. has been found suitable for the purpose. The vapor pressure of such an aly at normal operating temperatures is low and permits use of the alloy without the probability that the gaseous conduction effects will be seriously altered by any vaporization of the electrode material. According to the invention disclosed in the first of the co-pending applications above referred to, the upper surface of the liquid should be separated from the face 14 of electrode 12 by a distance comparable to the mean free path of the electrons in the gas, that is a distance such that electrons traveling directly across the gas s ace between the electrodes produce insufcient ionization to initiate substantial conduction, the mean free path of the electrons being understood to be the average distance traversed by the electrons without ionizing impact with gas molecules or atoms. Conduction is caused to take place through the action of a magnetic field produced bya magnet 22 having an internal pole and an ex- 7 ternal annular pole 21 arranged in such a manner that the surface of the liquid electrode is in a stronger magnetic field than the anode. To this end, the top of the magnetic poles are placed on a level slightly below the surface of the liquid electrode, as indicated in Fig. 1. Since the above mentioned alloy of sodium and potassium is liable to attack glass in its heated state, it is desirable to conne the operative part of the electrode to a portion which is removed from the glass walls. To this end, an annular cup-shaped electrode 30 is inserted in the liquid material. This electrode is provided with openings 32 to allow a slight circulation of the alloy. In this manner that part of the alloy which is heated to a high temperature by the discharge is confined by the cup 30 and the remainder of the alloy which is in contact with the glass is maintained at a safe temperature. The receptacle 10 may be filled with any type of gas of such pressure as to have its mean free path corresponding to the distance between the electrodes, as previously described. It has been found that the most suitable gas for this purpose is helium. In order to allow the apparatus to be connected in electrical circuits, suitable lead wires 24 and 26 cooperate with electrodes 12 and 16, respectively.

The apparatus shown in Fig. 2 de ends upon the formation of a space charge 0 positive ions for its rectifying action. .The apparatus includes a suitable'receptacle 50 of insulating material such as glass, in which are immersed cooperating electrodes 52 and 54. The cathode 54 is provided with an opening 58 which communicates with a hollow space completely surrounded by a shell 56 ergcept for the opening 58. This electrode is normally adapted to act as cathode. opposing faces of the two electrodes are spaced apart a distance which is short and of the order of magnitude of the mean free path of electrons in the gas, the receptacle being filled, as before, preferably with helium. The liquid material for the cathode is indicated at 60 and in this case is preferably pure tin substantially unalloyed with other materials. This metal has a melting point of ap proximately 232 C. and a boiling point of approximately 2270 C. The electrodes are preferably constructed with downwardly The sloping opposing faces as indicated in the current generatorv 40, a transformer 41 and a suitable load in addition to the rectifying tube. The load'will be supplied with electrical energy only when the direction of the current is such as to make the hollow electrode 54: negative.

Although the present invention has been shown as embodied in rectifying apparatus employing electrodes spaced apart a distance comparable to the mean free path of electrons in the gas, it is understood that the invention is not limited to these constructions but may be embodied in any apparatus cmploying an ionized gaseous region as a medium for electrical conduction, as, for example, in amplifiers, oscillators, etc. regardless of the spaces between the electrodes.

The invent-ion having been. described, what is claimed is:

1. Electrical apparatus comprising an elec trode which is liquid at operating temperature, an opposing electrode, the electrodes having therebetween a gas space sufliciently short to prevent substantial ionization by electrons traversing the shortest paths between the electrodes, and means distinct from current carriers to cause electrons to follow longer paths in one direction of applied potential between the electrodes.

2. Electrical apparatus comprising an electrode which is liquid at operating temperature, an opposing electrode, the electrodes having therebetween a gas space sufliciently' short to prevent substantial ionization by electrons traversing the shortest paths between the electrodes, and electron controlling means to cause said electrons to traverse paths sufficiently long to initiate ionization when potential is applied between the electrodes in one direction, whereby current flows predominantly in one direction when alternating current is applied to the electrodes.

3. Electrical apparatus ctmprising an electrode which is liquid at operating temperature, an opposing electrode, the electrodes having therebetween a. as space comparable in length to the mean ree path of electrons in the gas, and magnetic means to cause elec trons to follow longer paths in one direction of applied potential between the electrodes.

4. Electrical apparatus comprising an elec trode which is liquid at operating temperature, an opposing electrode, the electrodes having therebetween a gas space comparable in length to the mean free ath of electrons in the gas, and means below t e plane of the surface of the liquid electrode to cause electrons emitted therefrom to traverse longer paths thflclll electrons emitted from the other electro es.

CHARLES G. SMITH.

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