US2492666A

US2492666A - Hydrogen-filled thyratron

Info

Publication number: US2492666A
Application number: US654564A
Authority: US
Inventors: Howard B Sloan
Original assignee: Sylvania Electric Products Inc
Current assignee: GTE Sylvania Inc
Priority date: 1946-03-15
Filing date: 1946-03-15
Publication date: 1949-12-27
Anticipated expiration: 1966-12-27

Description

Patented Dec. 27, 1949 UNITED, STATES "PA-TENT "OFFICE Howard B. Sloan, Swampscott, Mass., assignor to Sylvania Electric Products Inc., Salem, Mass., a corporation of Massachusetts Application March 15, 1946, Serial No. 654,564

This invention relatesto electron tubes such as thyratrons and particularly to hydrogen-filled thyratrons. The invention is especially applicable to tubes for producing short, sharp pulses, such as shown in my co-pending application Serial No. 585,491 filed March 29, 1945.

To increase the electron emission of such tubes, the base material, usually nickel, of the cathode should be extremely pure, much purer than any commercially available in the past. In addition, I have found that the addition of zinc to the tube is necessary to secure a low voltage drop, although the exact function of the zinc is not fully understood. The zinc may be added to the tube in any convenient manner, and some will generally remain on the glass of the tubeunless driven ofi, but some of the zinc must be condensed on the part of the tube to secure the desired results. In one case, for example, where all the zinc was condensed on the glass, the voltage drop was 1 57 volts; when the zinc was driven back onto the electrodes of the tube by vaporizing it from the glass wall, the voltage dropped to 88 volts, about half its former value.

Other objects, features and advantages of the invention will be apparent from the following specification taken in conjunction with the accompanying drawings, in which:

Figure 1 is a vertical cross section of atub according to the invention; and

Figure 2 is a perspective view, partly in section, of an alternative construction for the top of the tube.

In the figures, the glass tube I has the lead-in wire 2 sealed through and closing one of its ends with the stem 3 through which additional lead-in

wires

4, 5 and 6 extend, sealed to and closing the opposite end. The tungsten filament coil 1 is attached at one end to the conductor 8 which supports it from the leadin wire 5 to which it is electrically connected. A coating oi refractory insulating material such as aluminum oxide is used on the filament turns to prevent short-circuiting thereof on sagging. The other end of filament coil 1 is connected by the metal tabs 9 and ID to the disc ll whose flanged edges l2 are attached to nickel cylinder l3, which is coated on its outside diameter with an electron emitting mixture of barium and strontium oxides.' This coating is best terminated a short distance from each end of the cylinder. The bottom of the cylinder is attached by the disc l4 through which the conductor 8 passes and from which it is spaced or insulated. A disc of larger diameter I5 is attached to'the disc I4 and extends beyond the 7 Claims. (Cl. 250-275) diameter of the cathode cylinder I3, to support the cathode shields l6 and l'l-which may be attached to the flange or rim ill at the outside-of the disc. The two cathode shields arepreferably spaced apart a short distance. The collar I 9 supported from the top of shield ll inturn supports the

shielding discs

20, 2| and 22 which are spaced from each other and attached to the collar I9 by the

conductors

23 and 24. The cathode shields l6 and H may be supported by the Wires extending from a collar 27 around the base of stem 3, to insure rigidity. I

Anode '28 is a circular metal disc attached to and supported by the lead-in wire 2 over which the glass bead 29 extends from seal3ll to a point close enough to the anode 28 to prevent flash over. The glass tube 3| concentric with the bead and spaced therefrom, extends along the entire length of the bead and merges with the bead into the seal 30 through which the lead-in wire 2 extends to be attached to the contact 32 by the solder 33. A collar 34'around theiree end of glass tube 3| is attached to the transverse disc 35 which shields the top of the anode 28. The grid 36 of metal gauze is attached to the flange edge 31 of disc 35 at the top of anode 28 and to the collar 38 below anode 28 from collar 38. The perforated disc or grid 39 is aflixed to collar 38. The additional collar 40 connects the disc shield 4| to the grid 39 and spaces it therefrom. The anode 28 is thus completely surrounded by a structure comprising the

grids

36 and 39 through which electrons from the cathode 3 must pass to reach said anode 28. The spacing between the anode 28 and the metal cylinder 42 which helps to support it and also acts as an addition head shield for the cathode l3. Cylinder 42 is supported at its bottom by the wires 43and 44 which are sealed into stem 3. The conducting

ribbons

45 and 46 connect lead-in

wires

43 and 44 with the cylinder 42 to insure good electrical contacts therewith. Tabs such as 41 may be used to assist in connecting lead-in

wires

43 and 44 to the cylinder 42. The base 49 may be cemented to the bottom part of the tube l by the cement 50 and the lead-in

wires

4, 5 and 6 may be connected to the contact prongs known. short-path principle. not, for the. bead. 29,..jfiash.over icouldfloccur be- 5|, 52, 53, 54 of the base which are insulated from each other. Prong 52 may be connected inside the base to prong 5| by the jumper connection 55.

The tube is of course, evacuated and filled with hydrogen at a pressure of mm.

In operation current is passed through the filament 1 which serves to heatthe nickel cylinder l3 and the emitting vcoating upon it. The electrons emitted therefrom passthrough the gas in the tube and eventually through the

grids

36 and 39 to reach the anode 28. Thegridstfi and 39 can thus be used to control the'star'ting of the discharge as in the usualthyratrons andb'ecause, of the use of hydrogen asthe gas'filling the dis-'- charge will deionize rapidly when the anode'v'olt age is removed.

Prior to my invention the' eail uii iiydisgen in tubes of this sort was a serious problem. I find that in a tube of my novel construction however,

: e. h dr e isnct l ned. up a p ec ab y.=-. h

appears ibe e dth et .the..1e ee ro are. all. emittedf o t e o tsid -Q. e c i l3. and-passed threuslithe e fin space e w e the ,cylinder and, the shield Barium or strontium particl es. sputtered from the cathode willj be picked up jbythe inside surface of the shield I5. The combination. of-these barium and strontium ,..parti,cle s withthe hydrogen to form a hydride may be the cause of ,the-hydrogen clean upand in ,my particular construction the particles fall on the shield close to the tcathode, apparently un- .der suchequilibrium conditions as cause the hydrogen to e ;r mcved..th re rom. T e absence ofcathodecoating fromthe top 120 i the cathode insures that all the sputtered particles will come .from the. sides .of, the cathode ,Intubes prior to my invention .the. put ered par cl app r to ,have hadqa, comparatively free path through the interiorrofthe tube. a

Lfind also that 117.15 Well gimme the tube at currentsin exces ofthe n rmallt e m ni ..ele tr n emission, .oi-the cath de iorthe. t mp rature at which-it is operated. For eXample, -thecylinder l3 mayehave a...diarnet.e1:, oiltzinch aud.a,.hei 11t at each end of .the cylinder.-. Thisgivesa coated for. example. 0.8.0 inch, and will. notfiash ,over with the, gas pressure used, because of the well Howevenflwere it tween the grid structure.35,36;fiilandthemore remote parts of the lead-in wire, 2 inside the tube. The beading. prevents'thisIflaslrover and should may use an anode voltage. as high as,16,000.v olts jwithout flash over underithose conditions. The distancefrom the anode28 to the outered e, 56

floftheseal 30shou1dlbe, quite longto prevent ele tr lysis. at. he.. .;Eo he 9 eseu I find a distance of about 7.2 cm. to be sufiicient.

4 The distance inside the tube from the anode 28 to the inner edge 59 of the seal is more important, and should be about 5.3 cm. for the voltage used. The tube may be made somewhat shorter by making the seal in a reentrant form as shown in Figure 2. In this case the tube 58 extends into the enclosing envelope and outward again as tube v3| to be sealed to the bead29 at point 59, which hen extends upwardjout of the tube. lThe grid support collar 34 is theri'at'tached to thereentrant tube 58 as shown.

The oxidesin the coating on cathode 13 may,

. to. the oxides: by. heating during exhaust in the mannerwen-known to the art.

When"not"'ca'rrying current the voltage drop across the. tubemay be 16,000 volts, but when apion of su'ificient voltage to the grid 36 causes the'tube to fire and pass current, the voltage across the tube may be as low as 88 volts or less for a urrent. M1 00. ampere t remainin v lt- .age appearin in uel adi circuit...... e.sr .d. volta e....for-.fi 3i.thelt bemay be a ut. 150. volts n emejce althoush itisg uerall appl d. in

such transient form as to make its measurement difiicult. -s

, Thevoltages, andcuriientheregiven arefor the peak value of .thepmse. throuehthe, t as vtar as they. can be ascertained. I he averagecurrent through. he tube maybe lesstnenempere- The, zinc,.60is.shown on the glass/envelope I j in the.,-drawing, butsome .Qf..i,t will be present on he ele tr des cipthe tube-.....I.. some..cases,e s f- ..ficient. tracev of zi m y adhere.. 0 itheruarts if somezinevaporis present the furnace whi the, .e1ectrode -parts are ;fi1:e.d; .hydre en. ,for

cleansin prior .toinser ioniu t .e. ub al hou h I prefer, to, add some zinc oxidefon the, putside of skirtTwhen -the. ube,- s.. b ine assembl When the tubeis being exhausted; hydrogen. at

. 1i 0r..2 .mm. ..of.,mer ury. press reimay b pa through .the tube. and, thegoxidelheated, for ex- -.a p e y. high. frequency induc ion, wh reupo the oxide will be reducedwto' metallicfizincand vvaporized'onto.,the .tub e. parts... When the tube elements are further heateddur'ing the usualex- =haust procedure known to the .fart. t e zin W condense on the. glass at ,the;t0pfoi. thetube, as Shown. at. 60 1 in, the. drawing Aiterlthe bulb is finished and sealed, ,thQjZillQ may ,be driven, off

,the top.joi the. tube andontqthe, tube elements bylheating; inwa fiame..l h.e.. glass -whenthe zin has deposited. As previously stated, this willre- .duce .the; tube .voltase drop ajs .much as half, in

, 'one particular case from 157 to 88' volts.

What. I.jclaim 1st,. l; AnhelectronItubeicomprising a sealed envelope, aAiHing-of-hydrogen therein, electrodes therein, a'ndizinc on said electrodes.

2. An electron tubehavin'g a sealed envelope containing hydrogen at low pressurefand 'a' plu- "'ralit'y 'of'el' "ctr'dde enclo ed within 'saide nvelo'pe,

" was; steppe ant aining hydro'gen plural elec csdesmc'mdest; 9 2 i e @1 r o ed b y en ,th hb trot electrode inte and anode, said electrodes having a surface a hydrogen fill and enclosing a small quantity of zinc.

5. An electron tube comprising a sealed envelope, a filling of hydrogen therein at a low pressure of the order of 0.5 mm., an anode, a grid, and an oxide-coated cathode therein, and zinc on the surface of said anode, grid and cathode.

6. A thyratron having a sealed envelope, 9. filling of hydrogen therein at low pressure of the order of 0.5 millimeter, and electrodes therein including an anode, a grid and an oxide-coated cathode, said cathode having a base material of pure nickel, said electrodes having a. surface trace of zinc.

'7. An electron tube having a sealed envelope containing hydrogen at low pressure, and a plurality of electrodes enclosed within said envelope, said electrodes including an anode, a thermionic cathode and a grid interposed between said anode and said cathode, said cathode having a base material of pure nickel, an oxide coating on said base material, and a surface trace of zinc.

HOWARD B. SLOAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,172,568 Schroter Feb. 22, 1916 1,699,112 MacRae Jan. 15, 1929 2,089,325 Aldington Aug. 10, 1937 2,096,862 Spencer Oct. 26, 1937 2,399,003 Crapuchettes Apr. 23, 1946