US3401292A - Fluid cooled hollow cathode discharge tube - Google Patents

Description

G. CIRRI sept. 1o, 196s FIUID COOLED HOLLOW CATHODE DISCHARGE TUBE Filed June 17, 1966 0 2 d 5 M W INVETOR United States Patent O 3,401,292 FLUID COOLED HOLLOW CATHODE DISCHARGE TUBE Gianfranco Cirri, Florence, Italy, assigner to Fabbrica Italiana Valvole Radio Elettriche F.I.V.R.E. S.p.A., a

corporation of Italy Filed June 17, 1966, Ser. No. 558,381 7 Claims. (Cl. 313-32) ABSTRACT OF THE DISCLOSURE A cooling means for a hollow cathode tube used in spectrophotometry characterized in that the cathode holder is surrounded by a coaxial body which is spaced therefrom forming a cooling circuit substantially over the entire length of the cathode. An annular baille is mounted between the cathode holder and the coaxial body to form two separate pathways for the cooling fluid, the pathways Vbeing respectively connected to a cooling lluid inlet and outlet.

This invention relates to a hollow cathode turbe for `application in spectrophotometry.

Tubes of this type, as it is known, may be applied, for example, as wave length reference generators and to determine in conjunction with a 'burner and photoelectric cell, the contents of certain substances in a given sample material, as, for example, metals.

In applications of the latter type, a light beam emitted by the cathode and directed upon a photocell is absorbed by the llame to a variable degree due to the combustion of the substance to be determined, if this is the same as that of the cathode.

The content of the substance contained in the cathode may be determined by the light variations on the photoelectric cell.

The operating temperature of the tube must be as constant as possible so as to maintain the light emitted by the cathode constant, so that the light variations registered =by the photoelectric cell are those due to the presence of a substance in the flame similar to that contained in the cathode of the tube.

lFrom this point of view, it can then be understood, also with reference to other applications, how hollow cathode tubes used in spectrophotometry must be adequately cooled in order to st-abilize the operating temperature.

One object of this invention is precisely that of providing a hollow cathode tube with temperature stabilization means and adapted to insure constant and steady emission of light as well as a rapid achievement of a steady operating condition and cathode sputtering control.

A further object of the invention is that of providing a tube of the highest elliciency long life and linear response.

In this invention, the above objectives are achieved by ellicient cathode cooling and for this purpose the cathode support or holder is surrounded by a hollow element coaxial to it and the inner part of which is provided with means which help to define the fluid cooling circuit for the cathode.

Said cooling circuit substantially extends over the entire length of the cathode.

According to this invention, one of the ends of the hollow body has a tube extension which receives a tube for circulation of the fluid and which terminates at the top of the cathode with a bafile which divides the interior of the hollow body into intercommunicating chambers in which the cooling iluid circulates.

Another characteristic of the invention is that the an- Cir Patented Sept. 10, 1968 ode of the tube conveniently consists of an envelope which surrounds the cathode holder or support, and which extends beyond the cathode to be supported at one end by the bulb of the tube with which it is engaged by a suitable collar which also serves as a terminal clamp for polarity.

According to a further aspect of the invention, a metal tube element is provided between the cathode and the glass bottom or optical window of the tube and which tube element acts both as a second anode and a protection for the optical window.

The invention will now be described in detail in conjunction with the attached drawing, by way of example, and in which the illustration shows the cathode tube according to the invention.

The tube illustrated consists of a glass bulb filled with a rare gas, and having two complementary sections A1 and A2 communicating with each other and sealed air tight, as will be described hereinafter.

The end of section A1 is closed by a metal ybottom piece 10, the rim of which is connected, in air tight relation7 for example, by welding, to the rim of said section A1.

A tube shaped spigot 12 is secured air tight, for example, by welding, to said bottom piece and extends to the exterior of section A1 for a certain length. Spigot 12, in the case illustrated, for-ms an integral part of a hollow body 14, the interior of which communicates with the bore of said spigot or tube extension.

Body 14 is closed, air tight, at its other end, by flange 16 of a cathode support 18 extending into s'aid hollow -body and which is provided with suitable means, for example, threads, for securing cathode 20 of the tube which, as stated, is hollow.

The end of spigot 112, extending from section A1 is provided with a groove 24 which serves to secure a threaded vbushing 22 to the spigot itself and which is provided with an eye-bolt 24 to engage said groove. Groove 24' also serves as an electrical connecting means between thel electric power source and cathode of the tube.

A manifold 26 is secured in air tight relationship to the end of 4spigot 12 by means of a bushing 22 which is screwed to it. The manifold has an inner chamber 28 which is connected to a pipe connection 30 for the cooling lluid outlet. Manifold 26, in turn, is crossed by a tu'bel 34 which, passing through the inner part of spigot 12, communicates with the interior of hollow body 14.

Chamber 28 communicates with the inside of hollow body 14 through a port located between tube 34 and spigot 14.

The inner end 36 of tube 34 extends into -a bored space element 38 which is secured to the hollow body 14 which has an annular baille 40, `which divides the interior of hollow body 14 into two separate chambers.

It should be noted that manifold 26 which carries tubes 30 and 34 and bushing 22 forms a lixed separate unit which is mounted on the hollow cathode tube by introducing tube 34 into the central bore of spacer element 38 and by subsequently securing the bushing to the end of spigot 12 by eye-bolt 24 as previously stated.

Cooling of cathode 20 is obtained by means of the lluid which, after entering tube 34 and discharging at its end 36, strikes the bottom 15 of cathode support 18 and successively, after being guided in its path by the inner surface of baille 40, strikes the external side Iwall of cathode support 18 to reach the bottom end flange 16 of the latter, after which the fluid reverses its llow direction passing into the chamber formed by baille 40 and hollow body 14, the ports in spacer element 38, the space between tube 34 and spigot 12 and finally to dischar-ge from chamber 28 into pipe 30.

latter entirely surrounds the cathode itself and its entire surface is constantly in contact with the owing fluid.

The cathode cooling circuit above described ensures uniform and regular circulation of the cooling uid and thus a stability of temperature in the cathode which thus guarantees a constant emissivity of light.

Insofar as the rapid achievement of a stable operating condition is concerned, it should be noted that this is almost immediately achieved, by virtue of the eicient cathode cooling.

The hollow cathode tubes heretofore known required an average of approximately 20-30 minutes before reaching a stable operating condition and, moreover, were not suitable to provide a light emissivity sufficiently constant to consent the relative measurement in addition to absolute measurement, which it is possible on the other hand to obtain with the tube forming the object of this invention, by virtue of its constant emission of light over a given time.

In order to provide high efficiency and long life, the anode of the tube consists of an envelope or shield 50 having a cylindrical part 51 which surrounds most of hollow body 14 and a conical connecting surface 52 which extends beyond the cathode and is locked by a flan-ge 54 welded air tight between the edges of the two bulb sections A1 and A2.

The arrangement of the anode around the cathode results in a higher eiciency of the working discharge (taking place in the cathode cavity) because the parasite discharges (such as occur outside the cathode hole in the known tubes) are practically eliminated by virtue of the anode coaxial structure which is suitably sized according to the cathode dimension.

Moreover, this arrangement makes its possible to extend the tubes life to hitherto unknown limits as a result of the very great reduction in absorption of the rare gas contained in the tube itself, both because the ionized gases cannot come into contact with the glass parts of the tube and because of the suppression of parasite clischarges as well as control of sputtering emitted by the cathode (at constant temperature).

The edge of flange 54 conveniently extends to the exterior of the tube for connection with the anodic supply.

The bulb is then closed air tight at the end of section A2 by a transparent lglass bottom plate 60 representing the optical window and connected to the bulb by metal parts consisting of a ring 58 and liange 56.

Although the spectrophotometric tube as illustrated and f described has provided excellent results, it was noted that this could be further improved by the introduction of suitable changes.

We have noted in fact that under some operatin-g conditions or with certain filling gases or cathode materials, the optical window of the tube may not be sufficiently protected from the cathode sputtering, and that its transparency may consequently be reduced.

To insure the best efiiciency of the tube, under any and all operating conditions, with any type of lling gas or cathode material, a hollow metallic element or tube 61 is placed between the cathode and the optical windo-w 60, said metal element 61 having a cone shaped flange 62 by which it is secured to metal ring 58. The other end of the tube is free and extends to the neighborhood of the cathode.

The above hollow element 61, the length and internal diameter of which are suitably proportioned to the dimensions of cathode 20 and function of the tilling gas, provides a protection of window 60 from the cathode sputtering and also contributes, if suitably polarized with respect to the cathode and coaxial anode 50-52, to avoid the formation of parasite discharges, with consequent improvement of the efficiency of the work discharge and life of the tube.

In the latter function it acts as a second anode for the tube, polarization being insured by ring 58 of the bottom plate.

I claim:

1. A hollow cathode tube for spectrophotometry provided with cathode cooling comprising glass bulb means, hollow cathode means, means to suppont said cathode in said bulb including a hollow body and a tubular portion integral with one end of said body and extending out of said glass bulb, an annular chamber formed by said hollow body being co'axially ymounted spaced from said cathode and extending over substantially the entire length thereof, means for mounting said cathode in the free end of said hollow body, annular baffle means coaxially mounted in said chamber forming inner and outer separate uid pathways, cooling uid inlet means passing through said tubular :portion and integral with said baflie to feed only said inner pathway, cooling fluid exhaust means connected to said tubular portion no receive cooling fluid from said outer pathway, means for supplying power to said cathode, anode means comprising an envelope coaxially mounted about said hollow body, said envelope comprising a cylindrical portion and an integral conical portion the flared end of which extends beyond said cathode so that coolant discharge will not affect the glass bulb, said conical portion extending through said glass bulb thus forming electrical connection imeans for said anode.

2. A hollow cathode tube according to claim 1 further comprising manifold means, said manifold means being mounted in air-tight relationship on said tubular )portion 0f said cathode support, ring means and locking terminal means sealing said manifold on said tubular portion, electrical connection means for said cathode formed by said ring means, locking tenminal means and cathode supporting means.

3. A Vhollow cathode tube according to claim 1 further comprising an voptical window formed in said glass bulb, a hollow metal element xedly mounted axially between said cathode and said optical window.

4. A hollow cathode tube according to claim 3 further comprising -a metal ring secured to the periphery of said optical Window, one end of said hollow metal element being secured to said ring and the other end of said hollow metal element terminating in the neighborhood of said hollow cathode.

5. A hollow cathode tube according to claim 3 in which said hollow metall element is a tube.

6. A hollow cathode -tube according to claim 4 in which said hollow metal element has a conical flange on one end thereof, said ange being secured to said ring.

7. A hollow cathode tube according to claim 3 in which said hollow metal element forms a second anode which is suitably polarized with respect to said cathode and first anode.

References Cited UNITED STATES PATENTS 2,647,218 7/1953 Sorg et al 313-247 2,802,125 8/1957 Nedderman 313-32 2,807,746 9/1957 Gardner et al 313-32 X 3,305,742 2/1967 McCune 313-36 X l AMES W. LAWRENCE, Primary Examiner.

D. J. GALVIN, Assistant Examiner.

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