US1880014A - Gaseous conduction device - Google Patents

Description

Patented Sept. 27, 1932 UNITED STATES PATENT OFFICE VANNEVAR BUSH, WEST MEDFORD, MASSACHUSETTS, ASSIGNOR TO RAYTHECN, INC., 0] CAMBRIDGE, MASSACHUSETTS, A CORPORATION OF MASSACHUSETTS GASEOUS connocrron nnvrcn Application filed April 14, 1925. Serial No. 22,988.

752,867 and particularly to gaseous conduction rectifiers adapted for small currents and low voltages such as used in radio receiving circuits.

Objects of the invention are to provide a device which can be manufactured economicall which may be installed and used by unskil ed operators, and which is economical and durable in operation.

In one aspect the invention involves a hollow cathode or other electrode having openings therein to which are presented anodes 'or other electrodes together with means for causing the electronic discharge between electrodes to pass through the openings. Said means comprises insulating material surrounding the anodes and substantially closing the spaces between the cathode and anodes around said opening. Said spaces or the gas spaces between the anodes and the peripheries of the openings or both preferably have a dimension which is comparable to the mean free path of electrons in the gas or at least so short that electrons traveling across the space roduce insuflicient ionization to initiate substantial conduction. The anodes are preferably disposed on the same side of the hollow cathode so that all the electrodes may conveniently be mounted on a common support and connected to the base of the tube.

In another aspect the invention involves an obstruction having openings therein, anodes presented to the openings from one side of the obstruction and a cathode or other electron emanating means disposed on the other side of the obstruction as hereinafter disclosed. By the clause anodes presented to the openings is meant the establishment of a'discharge path through the openings regardless of the relative position between the latter and each of the electrodes. The obstruction is preferably a part of the cathode. in which case, the surface of the obstruciion may function as an active cathode surace.

For the purpose of illustrating the genus the stem 8 by means of a ring 13 surrounding of the invention typical concrete embodiments are shown in the accompanying drawmg in wh ch 1g. 1 1s a side elevation with portions broken away;

Fig. 2 is a longitudinal central section on line 2-2 of Fig. 1;

Fig. 3 is a transverse section on line 3-3 of Fig. 2;

Fig. 4 is a central longitudinal section of a modification; and

Fig. 5 is a transverse section on line 55 of Fig. 4.

The particular embodiment of the invention shown in Figs. 1, 2 and 3 comprises a tube 1 which may be formed of glass, a hollowcathode 2, anodes 3, a block of insulation 4 which is preferably lavite, and a base comprising pressed metal shells 5 and 6 secured together by insulation material 7 The glass tube 1 has a reentrant stem 8 provided with two tubular projections 9 which extend into recesses in the bottom of the insulation block 4, the block 4 being slipped over the projections 9 and held in position by the cathode 2. The anodes 3 are mounted in openings in the block 4 concentrically with the projections 9 and the openings 10 in the cathode. The cathode is preferably formed in two parts, the upper part comprising an inverted cylindrical cup and the lower part 11 comprising a cover fitting over'the open end of the cup, the openings 10 being provided in the cover 11. The insulation block 4 is provided with circular recesses 12 adjacent the openings 10, the distance between the walls of these recesses and the anodes preferably being of the order of the mean free path of electrons therein. The peripheries of the openings10 are preferably bent downwardly to fit into the recesses 10 as illustrated in Fig. 2. While the cathode may be supported solely upon the block 4 it is preferably supported at least in part directly upon the stem and legs 14 extending to opposite sides of the cathode, the upper ends of the legs preferably being spot welded on the cathode cup at 15.

The rings 5 and 6 of the base are inter- 10c connected by being molded in the insulation material 7 and the tube 1 is mounted in the ring 5 by means of fusible material 16. The ring 5 is connected to one anode through lead 17, the ring 6 is connected to the other anode through lead 18, and the cathode is connected to the central contact 19 of the base throu h lead 20. With this arrangement all of t e electrodes are mounted upon the lower end of the tube and all of the leads connect with separate contact portions of the base. The device may be mounted in an ordinarfi socket 21 having contacts engageable wit the contacts 6 and 19 by provlding an additional contact 22 for engagement with the rinlg 5.

he modification shown in Figs. 4 and 5 comprises a tube 31, cathode 32, anodes 33, insulation 34 and a U-shaped wire 35 for anchoring the cathode on the block of insulation 34, the ends of the wire 35 being secured to the block by means of a wire ring 36. The lower end of the cathode is provided with openings 37 concentric with the anodes 33, the peripheries of the openin s being turned upwardl to form flanges. e insulation 34 is provi ed with recesses 38 surrounding the ends of the anode. The parts are mounted upon reentrant stem 39 in a manner similar to that described in Figs. 1, 2 and 3, and the tube may be provided with any suitable base as for example a bayonet type or a base such as shown in the former figures.

For rectifying purposes the anodes may be connected to opposite sides of the'secondary 'of a transformer 40 and the direct current circuit 41 ma be connected to the cathode and a central tap of the transformer secondary as shown in Fig. 4.

The interior of the tube may be filled with a suitable gas or gases, preferably monatomic gases at suitable pressure, for example, the

gas may comprise helium at 13 mm. pressure.

The inner surface of the cathode is preferablly coated with an oxide of an alkali earth meta such as calcium, strontium or barium to decrease the voltage dro at the cathode.

One method of applying t e coatin is as follows: The on is coated on the insi c with a layer of meta lic calcium which may then be oxidized in order to provide an oxide coating, although it is not essential that the coating be oxidized. Inasmuch as calcium melts at about 800 C. and sublimes in a vacuum at about 720 C. it will va orize onsequently a small piece of calcium is placed in the cathode cup, which may be formed -of iron or copper, and the device is then connected to suitable pumping apparatus. The tube is exhausted to a hard vacuum and the cup and other metal parts heated to about 650 C. by means of a high frequency coil surroundin the tube. At this temperature the gas w1 leave the metal parts and temperature.

the impurities will be removed from the surfaces, leaving the metal parts clean. However the calcium will be unaflected at this The tube is then filled with helium to the operating pressure, say 13 mm. and a hi h frequency field is again applied to heat t e cu to about 850 C. for a short period.' At t is tem crature the calcium melts and flows over t e internal surface of the cup by virtue of surface tension. However the calcium does not vaporize in substantial degree because its vapor pressure is only about 10 mm. and the vapor can only difi'use slowly through the protecting atmosphere of helium. Incidentally the calcium absorbs impurities during this process, leaving the helium free from active gases. The tube may then be sealed off for use. However in case an oxide coating is desired a small amount of pure oxygen is admitted to the tube before sealin it off. If this is done before the tube is coo ed the oxygen will combine with the surface calcium and make a hard coating of oxide. Other metals of the oxide group such as strontium or barium may be employed, but for most purposes calcium is superior. If it is desirable to coat the cathode at lower temperature or a. lower gas pressure in the tube this may be accomplished by using a coating material, such as calcium m gnesium alloy, which has a lower melting tem inerature.

An alternative method of coating the cathode consists in dipping the cup in molten calcium or other suitable material in an inert atmosphere such as argon, thus coating the cup with a thin layer of calcium. A similar process consists in enclosing the cup in a tight container with the alkali metal and heating the whole, the metal combining with the small amount of air present and then sublimes over the surface of the cup. The cup is then assembled in the tube, the tube exhausted and then filled with helium to working pressure, and then sealed off. After bein sealed off the tube is raised to a red heat, eit er by aseous discharge between the electrodes or y use of a high frequenc field. The gas which is driven ofi from t e metallic parts will then be absorbed by the alkali earth metal, leavin pure helium. The lower part 11 of the cat ode may be similarly treated.

This coating has a unique function in a glow-discharge tube (lin contradistinction to a high vacuum tube) raving a metallic cathode operating at a temperature below that at which conduction is largely dependent upon thermionic emission (in contradistinction to an incandescent thermionic cathode?l in that it serves the two-fold purpose of hot reducing the voltage drop of the tube and also restraining gas clean-up, that is the permanent entrapment of gas molecules in the metal of the cathode due to ion bombardment of the cathode as a result of the comparatively high voltage drop in tubes of this type. This function is, of course, peculiar to tubes of this character since the problem of clean-up does not arise in thermionic tubes in which the incandescent cathode is comparatively free from deleterious ion bombardment because of the low voltage drop resulting from the use of an incandescent cathode. In my prior Patent No. 1,617,181

without the use of special cathode material as in my prior patent.

In operation space current flows between the cathode and one of the anodes when the cathode is negative and the anode is positive.

- Inasmuch as the anodes are alternately positive current flows alternately between the cathode and the two anodes respectively. Current is prevented from flowing in the reverse direction by causing substantially all of the electronic discharge to pass between the ends of the anodes and the interior of the cathode. Current is prevented from flowing between the anodes and the periphery of the openings in the cathode by making these gaps so short that electrons flowing across t e spaces produces insuflicient ionization to initiate substantial conduction. Gaseous conduction between the anodes and the exterior of the cathode is prevented by the insulation block 4; and by providin recesses such as 12 and 38 the tendency of t e current to flow between cathode and anodes along the surface of the insulation is prevented or reduced to a negligible factor. It has been found that the a effectively by roun mg the ends of the anodes as shown in Figs. 2 and 4.

From the foregoing it will be evident that the cover 11 of the cathode cup 2 (or the bottom of the cup 32 in Fig. 4) constitutes the obstruction herein referred to by virtue of which gaseous conduction is restricted to the space between the ends of the anodes and the interior of the cathode.

Owing to the fact that the regions ad aeent the ends of the anodes intercommunicate inside the hollow cathode the device produces less disturbing noises when used for radio or telephony ur oses than in the case of a separate catho e c amber for each anode.

I claim:

1. In a glow discharge device comprising a sealed container containing a cathode, an anode, and a gas at a pressure sufiiciently high to support a dischar e between said cathode and anode with su stantial ionizaaratus functions more tion, said cathode bein of metal and operathe cathode, and then oxidizing said material to produce a surface for the purpose of .reducing potential drop and also of restraining gas molecules from being permanently embedded in the metallic cathode of sufiicient degree substantially to reduce the gas pressure durin prolonged operation of the tube.

2. In a g ow discharge tube containing gas at a pressure of the order of magnitude approximating 13 millimeters of mercury to transmit current by gaseous conduction and having a metallic cathode o rable at a temperature below that at which conduction is largely dependent upon thermionic emission, the method which com rises applfying alkaline earth material to t e surface 0 the cathode and oxidizing said material to produce a hard surface for the purpose of reducing potential drop and also of restraining as molecules from being permanently embed ed in themetallic cathode in suflicient degree substantially to reduce the gas pressure durin prolonged operation of the tube.

igned by me at Cambridge, Massachusetts, this tenth day of April, 1925.

VANNEVAR BUSH.

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