US1931299A - Gaseous conduction apparatus - Google Patents

Description

Oct. '17, 1933. P. L. SPENCER GASEOUS CONDUCTION APPARATUS Filed Aug. 24, 1928 w T m W l M TTOQNEY Patented l 1,991,299 GASEOUS CONDUCTION arraaa'rus Percy; L. Spencer, Medford, Mass.,-assignor to Baytheon, Inc., Cambridge, Mass., at corporation of Massachusetts Application August 24, 1929. Serial no. 901,99

1 Claim. (01. 250-215) My invention relates to gaseous conduction apparatus and particularly to improvements in rectifiers of the gaseous conductiontype. Rectifiers of this type have been known and used to 6 a large extent. The type of rectifier to which my invention pertains is particularly characterized by the fact that the electrodes are in general non-thermionic. Such rectifiers have ordinarily been used in circuits where the voltage was 300 or less between cathode and anode. Although this type of rectifier may, and very often does, successfully rectify higher voltages, such rectification is ordinarily beyond the capacity of the tube and generally results in greatly shortened life. For many purposes it is highly desirable that voltages up toseveral thousand be successfully rectified. The simplicity of mechanical construction, ease of starting and operation, and efilciency of this type of rectifier make it highly suitable for pur- 20 poses where currents under one ampere are required. My invention aims at so improving the gas type of rectifier that it will successfully withstand voltages of 2000 without losing its unilateral conductivity.

In gaseous conduction devices it is well known that an increase in the pressure of gas used results in a heavier discharge current and lower potential drop across the electrodes. n the other hand, such high pressure is accompanied by low resistance to back voltage. This is because with a given electrode spacing, a high pressure gas has on the average more gas particles in the inter-electrode space to be ionized by electrons from the cathode. Such ionization results in a cumulative'buildin'g up of a heavy discharge.

In order to obtain desirable insulating characteristics for reverse potential, a tenuous and highly rarefied atmosphere is desirable. By my invention, I am enabled to combine in. one tube the advantages of the presence of a gas at high pressure between electrodes when discharge ocours and a low pressure between electrodes on member from ionic bombardment. This shield reverse potential. By thus combining these two features, advantages inure to the tube to give it highly desirable characteristics.

An additional feature of my invention resides in the construction of the container, especially near the seals. The proximity of the region of discharge to seals results in raising the temperature of the glass at those points so that suflicient conductivity to result in electrolysis at the seals,

is brought about. Furthermore, the mass of glass at the seals, as well as the presence of metal, renders it highly desirable that they be kept cool.

552 'By my construction, the container is-so shaped that the seals are protected from any undesirable action.

In general my invention comprises an insulating vessel in'which are at least two electrodes spaced apart from each other in an atmosphere 6 of some gas, preferably of the rare group, such ashelium. The anode may be of any shape whatsoever and preferably is so shaped that it presents a relatively small amount of active surface. Spaced apart from this anode is a cathode. The spacing between the cathode and anode should not be too great because the starting voltage as well as voltage drop become undesirably high. 0n the other hand, the spacing should not be too small because the gas pressure in the tube as a whole is low and hence, but little current could pass through the tube. The cathode is a thin member and has a concave active surface and preferably such a surface as might be formed by revolving any plane figure about an axis.

The anode may be constructed of iron, carbon, tantalum or any other suitable material. The cathode may be of suitable refractory material, the active surface of which is treated in such manner that it has a low .work function. Preferably the cathode consists of a thin sheet of tantalum which has been specially treated. The active surface of the tantalum iscoated with solutions of nitrates of various metals of the alkali and'alkaline earth group, such as barium and strontium. These nitrates are thereafter burned into the tantalum by an intense flame. This process is repeated several times causing the tantalum to become somewhat brittle and assume a whitish and crusted appearance. Cathodes treated in this manner have been found to be very eflicient and desirable, not only in this tube but in othertubes as well. The cathode and process of makingit is claimed in a copending case of mine, Serial No. 289,845, filed Ju1y2,1928. The anode-is preferably protected by a shield member of metal actsnot only to protect the anode, but also the extreme edges of the insulation around the anode. A shield also protects the cathode insulator. 1

The seals are protected from harmful influences by causing the container to assume a 1'9. entrant shape-near the seals. An insulator fills 105 up the space adjacent the seal on the inside. The glass surface near the seal is so extended that there-is little possibility of the seal ,becoming hot. i

Electrons emerging from the surface of a 9 repulsion go off in all directions.

cathode leave itin a generally normal direction. It is obvious that space charge due to other electrons as well'as the direction of the electrostatic gradient may change in some degree the angle of emission. Electrons leaving the entire surface'of the cathode as disclosed here, in this general way will tend to meet in a region along the axis of the concave surface of the cathode. This focal region in a geometrical sense may be anything from a point to a solid region depending upon the shape of the active surface. The actual electronic focal region can never be very sharp because of the tremendous repulsion between electrons. Electrons in going to the focal region cause ionization. 4 Both the electrons and ions will congregate in the focal region resulting in a dense conglomeration of electrons and ions. Such a condition will make for more intense ionization by electrons coming from the cathode. The electrostatic gradient will draw the electrons to the anode. Since the focal region is a region of intense ionization, a copious supply of electrons is assured and a heavier current will be passed through the tube.

Electrons in leaving the cathode surface and traveling toward the focal region have a tendency to push all gas particles and ions, which they encounter, into the focal region, thus setting up a region of comparatively high pressure there. As stated above, this is conducive to the establishment of a heavy current through the tube.

On reverse potential any electrons leaving the anode surface are not focused and due to their Most of the electrons are, therefore, rendered harmless and useless as far as initiating a reverse discharge is concerned.

Furthermore, whatever ionization may occur is scattered and ineffective. This is equivalent to having a gas at very low pressure on reverse potential.

A tube of this character has been found to rectify a current of over a quarter of an ampere' at 2,000 volts.

In operation, the tube is characterized by a luminescence which is glow-like as far as characteristics are concerned. When starting under no load or very light load, the tube exhibits a diffused glow extending beyond the confines of the inter-electrode space. This glow is most 1ntense at the center in the space between the cathode and anode. This intense spot is generally located well within the concave active surface of the cathode and appears to be distinct therefrom. As the load is increased, the diffused portion of the glow appears to shrink while the intense portion enlarges. At the same time this intense portion of the glow comes closer toward the anode along the axis of the cathode. At full load the entire discharge through the tube is concentrated in an intense ball of fire between the cathode and anode and distinct from both. There is little or no glow visible out- The drawing shows a sectional view of a tube embodying my invention, the tube being approximately one half size.

A container 1 of glass or any other insulating material has elongated ends 2 with reentrant portions 3 and 4. There is thus a considerable cooling surface near the seals, keeping them cool. Mounted in portions 4 are insulators 5 of any suitable material such as lava or the like. Theseinsulators may be disposed in any suitable manner and are preferably so disposed as to fill up and snugly lit the space within portions 4. Passing through the center of one of insulators 5 in an anode 6 of any suitable material. At one end of the anode is connected a lead wire 17 suitably sealed as it passes through the glass. Anode 6 projects a short distance beyond the end of insulator 5. Within a circular groove 7 around insulator 5 and near one end thereof, is retained an outer shield member 8 and an inner shield member 9. Outer member 8 has-a hole 10 which is slightly larger than the diameter of anode 6. Inner shield 9 has its edge adjacent the anode bent over so that the edge forms a hole somewhat larger than anode 6. Anode 6 preferably is disposed with its end below the hole 10 of shield 8 and a little 'above the upturned edge of inner shield 9. 4

Through other insulator 5, lead 18 suitably sealed where it comes through the glass, emerges beyond the insulator and supports a cathode 15. This insulator also has a groove 7 supporting a shield member 11. The cathode may be supported on the wire in any su table way, as by welding. As shown here, the cathode consists of a conical member, the inner surface of which a has been rendered active as previously stated.

However, the shape of the cathode is not restricted to that of a cone. The cathode may be ellipsoidal, parabaloidal, or any other desirable shape. The distance between the tip of anode 6 and cathode 15 is such that anode 6 is substantially at the tip of cone 15 reversed. Anode 6 is at the axis as shown. However, if more than one anode is to be used, they may be placed within a short distance of each other and occupying approximately corresponding positions.

The tube is exhausted in accordance with usual practice and the electrodes are freed of occluded gases. Thereafter, any gas at a low pressure is introduced within the vessel. Preferably helium at a pressure of about 6 m. m. is used.

When the tube operates, it is evident that the portions of the glass stem nearest the region. of discharge protect the seals. By making the stems reentrant, a large surface is exposed to the air allowing the heat to be dissipated and keeping the seals cool.

What is claimed,

A unidirectional gaseous discharge tube of the type wherein the discharge .is initiated in the form of a glow, comprising an evacuated en-

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