US2916646A

US2916646A - Gas discharge tube

Info

Publication number: US2916646A
Application number: US593975A
Authority: US
Inventors: David A Rohrer
Original assignee: Beckman Instruments Inc
Current assignee: Beckman Coulter Inc
Priority date: 1956-06-26
Filing date: 1956-06-26
Publication date: 1959-12-08
Anticipated expiration: 1976-12-08
Also published as: FR1178524A; CH354517A; GB861055A

Description

Dec. 8, 1959 D. A. ROHRER GAS DISCHARGE TUBE Filed June 26, 1956 H. R 68 Y Em H RREOQ oH fi R v mAmm Y m m A s D m R adjacent the end of the other.

United States Pater 11:07

GAS DISCHARGE TUBE I David A. Rohrer, Whittier, Calif., assign'or to Beckman Instruments, Inc-., Fullerton, Calif., a corporation of California Application June 26, 1956, Serial No. 593,975

11 Claims. (Cl. 313-.-117) My invention relates to gas discharge tubes for producing spectral radiation of a selected wave length or wave length band. It will be particularly exemplified as applied to a low voltage or thermionic hydrogen tube opening which constricts the discharge,

It is an object of the present invention to provide separate cathode and anode enclosures, preferably disposed at different elevations and with the end of one A further object is to dispose an open-ended cathode enclosure'with one end adjacent the discharge-constricting opening, preferably in such manner that the cathode-induced thermal circulation of the gas inside the tube is past such opening. 'Inthis way, the cathode enclosure serves as a common chimney for heat from both the cathode and the intense glow discharge spot at the discharge-constricting opening. A

further object is to support and energize the cathode exclusively from the other or opposite end of the cathode enclosure, thus simplifying construction and leaving unobstructed that end of the enclosure adjacent the anode enclosure. 7 H

A further object is to provide anode and cathode enclosures of tubular form and, in the preferred embodiment, to support same in end-to-end relationship with their axes substantially on the same "straight line. A further object is to provide a simplified internal support for the anode and cathode enclosing structures, and to dispose the discharge-constricting aperture at the end of one of the enclosures, typically in a plate closing the open end thereof and sloping with respect to a line joining the aperture and the window of the tube envelope.

A further object is to construct a gas tube that will fire reliably over a much wider range of internal pressures than older-type tubes, thus making it possible to lengthen tube life and improve convective cooling within the tube by initially filling the envelope at higher pressure. Still a further object is to reduce the mass of metal and the areas of metal surfaces within the tube, making it easier to out-gas the tube and minimize the metal surfaces which may absorb or react with the internal gas. A further object is to simplify and reduce the manufacturing costs of such gas discharge tubes, while also adjusting the internal geometry to shorten the anode-cathode path and eliminate the necessity of cathode-produced electrons making a right angle turn to reach the anode.

through, this circulation being spaced from the small 2,916,646 Patented Dec. 8, 1959 to insure adequate out-gassing thereof. It is an object of the present invention to eliminate such ashield. Even though the radiation is thus exposed more directlyto the window of the tube, it has been found that the new design .produces appreciably less darkening of the window from evaporation of metal near the discharge constriction. The reason for this improvement is not yet fully understood, but the beneficial effects have been proved by prolonged tests.

It has also been found that the spectral discharge of thepresent invention is particularly steady in intensity. In former designs, the current distribution in the discharge tended to vary, causing slow changes in the observed intensity of the discharge. This instability may have resulted from having a discharge path ,at right angles to the convective flow path. In the preferred embodiment of the present invention, the discharge path is in a similar direction to the convective gas stream, leading to greater stability.

Further objects and advantages of the invention will be evident from the herein-contained description and illustration of a preferred embodiment of the invention.

Referring to the drawing illustrating such preferred embodiment:

Fig. 1 is a longitudinal mid-sectional view of a typical hydrogen tube; a

Fig. 2 is a sectional view taken along the line 2-2 of Fig. 1;

Fig. 3 is a fragmentary view of the upper end of the cathode enclosure, taken along the line 3--3 of-Fig. 2;

Fig. 4 is a section of the getter, taken along the line 44 of Fig. 3;

Fig. 5 is a sectional view of the anode enclosure, taken as indicated by the line 55 of Fig. 2; and

Fig. 6 is a fragmentary perspective viewof the anode.

The hydrogen tube illustrated in the drawing comprises the usual glass envelope 10 blown to provide a thin window 12 through which the radiation passes with little disposed end to end .are preferred. One of the adjacent ends is constricted to form a discharge-confining aperture 25 through which the discharge current flows in a path extending from a cathode 26 to an anode 28. The

aperture 25 is preferably formed in a two-part plate 29 closing the upper end of the anode enclosure 22 and positioned to dispose the aperture opposite the window 12 and adjacent the lower open end of the cathode enclosure 23. The plate 29' is shown as sloping or disposed 0bliquely with respect to a line joining the Window and the aperture. The aperture 25 is formed in a thin wall 30 closing a larger opening in a flanged member 31 attached to the anode enclosure 22 by a Weld or press fit between the flange and a tubular body 33 of the anode enclosure 22. The wall 30 is preferably formed of tungsten.

. The anode enclosure 22 is preferably made of sheet metal, typically nickel. A sturdy structure results by 3 making the tubular body 33 of semi-circular sections of a strip of nickel, these sections being held together by tabs 34 welded together and by welded tabs 35 joined integrally with a circular section 36 of the strip. Through this circular section extends, in tight relationship, a p st member comprising a tube 37 of insulating material through which extends the conductor 16, the tube form- 'ing a part of the post 20 and being usually formed of a ceramic material. The other cathode-energizing conductor 17 is welded to a junction post member 38 to which one of the tabs 34 is in turn welded, thereby supporting the-anode enclosure 22 rigidly between the

posts

20 and 21 at a lower position.

The lower end of the anode enclosure 22 is tightly closed by a plug 40 resting on a neck 41 of the press 14. The anode. 28 is preferably a ring-like element made of tungsten and supported within the enclosure 22 by integral tabs 43 (Fig. 6) welded to the anode conductor 18. The plug 40 is formed of a ceramic material and becomes quite .hot at its upper end when the discharge tube is in use.

To'prevent any appreciable conduction across the upper face of the ceramic from the anode 28 to the enclosure 22 when the ceramic becomes increasingly conductive in heated condition, the upper face of the plug 40 provides an annular groove 44 which interrupts the conducting path across the face and prevents electrical leakage and overheating.

' The cathode enclosure 23 is preferably formed as an "open-ended tube of sheet metal, typically nickel, supported between the

posts

20 and 21 at an upper position by tabs 45 (Fig. 3) welded to the junction post member 38 and by tabs 46 welded together and joined integrally with a circular section 47 tightly encircling the upper portion of the insulator tube 37. As with the anode enclosure 22, this construction provides semi-circular sections forming a tubular body 49 of the cathode enclosure 23. The lower open end of the cathode enclosure is adjacent and preferably above the plate 29.

It is a feature of the invention that the thermionic cathode 26 is supported and energized exclusively from the other or upper open end of the cathode enclosure 23. 'As shown, the cathode 26 is formed as a helical oxidecoated filament with its two terminals respectively connected to the upper ends of the

conductors

16 and 17 by cathode support strips 51. The cathode is thus supported and energized from that end of the enclosure opposite the end that is adjacent the anode enclosure 22.

With the disclosed positioning of the

enclosures

22 and 23, there is nothing to impede the free intake of gas into 'the lower end of the cathode enclosure 23 as a result of the strong chimney action set up when the cathode 26 is heated. This sets up an internal convective circulation, indicated by the arrows 50, which not only gives a superior cooling action but carries to the upper end of the tube any atomic hydrogen formed by the intense electrical discharge in the aperture 25. This atomic hydrogen is converted to molecular hydrogen by contact with the upper interior surfaces of the glass envelope 10. This protects the more critical metal and glass surfaces of the tube from the action of the highly-reactive atomic hydrogen.

Other desirable results are also obtained by using the cathode enclosure as a common chimney for heat rising both from the cathode and from the intense glow discharge spot at the aperture 25. Thus, under certain circumstances it is found that small amounts of water vapor are formed, possibly from reaction of minute amounts of atomic hydrogen with the oxides of the thermionic cathode 26. If the upper interior of the envelope contains 'a chemical capable of reacting with water to take up the oxygen and release hydrogen, the chimney effect will transport the water vapor thereto with the result that the hydrogen within the tube will be replenished. In practice, a suitable metal is vaporized within thte envelope 10 during aging of the tube, as by vaporizing metallic barium to react with some of the hydrogen and deposit as a barium hydride coating 55 on the upper interior of the envelope 10. The chimney effect of the cathode enclosure 23 will thus transport water vapor and atomic hydrogen to the coating 55 for reaction therewith to form molecular hydrogen.

Such metallic barium is preferably flash-vaporized by induction heating from a position outside the envelope 10. Referring to Figs. 2, 3, and 4, an inverted U-shaped wire 58 is supported by an extension of one of the cathode support strips 51- with' its depending legs bridged by one or more arcuate barium-containing members 60. These members may be metal tubes 61 filled with barium metal and ground away at surfaces 62 to expose the barium for easy vaporization and escape when induction heating is applied.

The plate 29 is desirably out-gassed by inductive heating applied from a position outside the envelope 10. As the tube contains no internal shields between the plate and the envelope, the inductive heating can heat the plate without danger of overheating or melting the shield.

Before the upper tip of the envelope 10 is sealed off, the final hydrogen atmosphere is introduced. Heretofore, hydrogen tubes could. be fired reliably only if the internal. pressure was no more than about 7 mm. of mercury. The tube of the present invention has been observed to fire even at pressures as high as 50 mm, and it is common to sell the tube containing hydrogen at initial pressures of 15 mm. or more. Since the gradual loss of hydrogen in the tube is perhaps the most important single factor limiting tube life, a tube filled initially at a higher pressure will last correspondingly longer. Additionally, it has been found that the tube of the present invention continues to fire and operate reliably at pressures below those at which earlier tubes would fail, to function, thereby further extending tube life. It is believed that such new results arise in part from the fact that the distance from the anode constriction or aperture 25 to the nearest portion of the cathode 26 can here be made smaller than in tubes of. earlierv design; also because the present design eliminates the need for electrons in the cathode-anode path making a right angle turn.

The new design is easier to out-gas and can be constructed with internal metal surfaces less than half the area of previous designs. The new design necessitates lessspot Welding and reduces the amount of oxides, formed in such welding, which may subsequently consume hydrogen. In addition, it can be easily fabricated. A constructional feature of significance is that the

tabs

34, 35, 45 and 46 of the anode and

cathode enclosures

22 and 23 act as cooling fins therefor. If desired, these tabs may be extended to provide a further cooling action.

The exemplified embodiment will, suggest variations which can bev made without departing from the spirit of the invention as defined in the appended claims.

I claimas my invention:

1. A gas discharge tube for producing spectral radiation of a selected wave length band, said tube comprising: an envelope containing a gaseous atmosphere and having awindow for passage of said radiation; a cathode enclosure atv an upper position in said envelope; a thermionic cathode in said cathode enclosure increasing the. temperature within said enclosure when said cathode is energized, said cathode, enclosure being open at its upper and lower ends, there being a space around said cathode enclosure Within said envelope through which said upper. and lower ends are in open communication, said cathode, establishing a convective circulation of said atmosphere upward through said enclosure and down ward in said space therearound' in a closed path; an anode within said envelope below said cathode enclosure; an anode enclosure within said envelope enclosing said ano a d" anode. enclosure having an open upper end adjacent but below said lower end of said cathode enclosure, there being a discharge path between said anode and cathode traversing said adjacent ends; and means for severely constricting one of such adjacent ends to form a small discharge-confining aperture opposite said window to produce a spot of intense radiation localized at said small aperture.

2. A gas discharge tube as defined in claim 1 including a plate extending across said one of said adjacent ends, said plate having an opening forming said dischargeconfining aperture,

3. A gas discharge tube as defined in claim 2 in which said plate is disposed obliquely relative to a line joining said window and said small aperture.

4. A gas discharge tube as defined in claim 1 in which said cathode enclosure is tubular, and in which said discharge-confining aperture is on said anode structure and lies substantially on the extended axis of said tubular cathode enclosure.

5. A gas discharge tube as defined in claim 1 including a cathode support above said upper end of said cathode enclosure, and means for supporting said cathode exclusively from said cathode support in a position depending in said cathode enclosure from said support.

6. A gas discharge tube as defined in claim 1 in which said cathode enclosure is tubular and in which said anode enclosure has an axis lying along the downwardly extended axis of said tubular cathode enclosure, and including an upright support post in said envelope and means for mounting said enclosures end to end on said support post, said support post being displaced from a line joining said window and said small aperture.

7. A gas discharge tube as defined in claim 6 in which at least one of said enclosures is formed of sheet metal bent to form a sidewardly-extending tab connected to said support post to support the corresponding enclosure therefi'om.

8. A gas discharge tube as defined in claim 6 in which said support post includes a conductor means electrically connected to said cathode, and means for insulating said conductor means from said metal enclosure.

9. A gas discharge tube as defined in claim 1 including two opposite posts respectively connected to opposite sides of each of said enclosures to support said enclosures therebetween in endto end relation with said adjacent 6 ends spaced from each other, said support posts being spaced from a line joining said window and said aperture, at least one of said posts being hollow, and an electrical conductor extending through the hollow post and being electrically connected to said cathode in energizing relationship.

10. A gas discharge tube as defined in claim 9 in which said hollow post is formed of insulating material, and in which said electrical conductor traverses and is sealed to said envelope.

11. A gas discharge tube for producing spectral radiation of a selected wavelength band, said tube comprising: an envelope containing a gaseous atmosphere and having a window for passage of said radiation; a cathode enclosure positioned in said envelope; a thermionic cathode in said cathode enclosure increasing the temperature within said enclosure when said cathode is energized, said cathode enclosure being open at its upper and lower ends, there being a space around said cathode enclosure within said envelope through which said upper and lower ends are in open communication, said cathode establishing a convective circulation of said atmosphere upward through said enclosure and downward in said space therearound in a closed path; an anode within said envelope; a tubular anode enclosure enclosing said anode; means for mounting said anode enclosure and said cathode enclosure in end-to-end relation within said envelope, said anode enclosure having an end adjacent one of said ends of said cathode enclosure, there being a discharge path between said anode and cathode traversing said adjacent ends; and means for severely constricting one of such adjacent ends to form a small discharge-confining aperture opposite said window to produce a spot of intense radiation localized at said small aperture.

References Cited in the file of this patent UNITED STATES PATENTS 1,858,698 Zons May 17, 1932 1,951,137 Ewest n Mar. 13, 1934 1,954,420 Marvin Apr. 10, 1934 2,030,435 Fehse Feb. 11, 1936 2,030,450 Haucke Feb. 11, 1936 2,165,987 Sobczak July 11, 1939 2,228,327 Spanner Jan. 14, 1941