US3641385A

US3641385A - Gas-filled discharge tube with gas-refilling means

Info

Publication number: US3641385A
Application number: US49380A
Authority: US
Inventors: Taizo Oikado
Original assignee: Nippon Electric Co Ltd
Current assignee: NEC Corp
Priority date: 1969-06-30
Filing date: 1970-06-24
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08

Abstract

A unit for supplying gas to a gas-filled discharge tube includes a gas container and a reservoir in communication therewith. The reservoir has an outlet portion and valve means are provided at the reservoir outlet to selectively place the reservoir in and out of fluid communication with a chamber. The latter in turn communicates with the interior of the discharge tube.

Description

United States Patent Oikado 1 Feb. 8, 1972 [54] GAS-FILLED DISCHARGE TUBE WITH GAS-REFILLING MEANS [72] Inventor: Taizo Oikado, Tokyo, Japan [7 3] Assignee: Nippon Electric Co., Ltd., Tokyo, Japan 22 Filed: June 24, 1970 A 7 [2 1] Appl. No.: 49,380

[30] Foreign Application Priority Data June 30, 1969 Japan ..44/52065 [52] US. Cl ..313/l75, 315/110, 316/24, 331/945 [51] Int. Cl. ..H01j l7/26,1-101j 61/24 [58] FieldotSearch ..315/108,110;313/l75,180; 331/945; 316/11, 24

[56] References Cited UNITED STATES PATENTS 2,009,218 7/1935 Baumhauer et a1 ..3l5/l10 X 1,025,635 5/1912 Machlett ..313/175 3,566,304 2/1971 Neusel et a1 ..315/110 X Primary Examiner-Roy Lake Assistant ExaminerPalmer C. Demeo Attorney sandoe, Hopgood and Calimafde [57] ABSTRACT A unit for supplying gas to a gas-filled discharge tube includes a gas container and a reservoir in communication therewith. The reservoir has an outlet portion and valve means are provided at the reservoir outlet to selectively place the reservoir in and out of fluid communication with a chamber. The latter in turn communicates with the interior of the discharge tube.

2 Claims, 2 Drawing Figures PATENT Ema a 1972 FIG! INVENTOR. TAIZO OIKADO GAS-FILLED DISCHARGE TllBE WITH GAS-REFILLING MEANS This invention relates generally to gas-filled discharge tubes and, more particularly, to an improved laser discharge tube of the kind equipped with a gas refilling unit.

As is known, the useful life of a gas tube, particularly a laser high as several tens of amperes, the gas pressure within the tube decreases at a fairly high rate, thereby adversely affecting the life of the tube. To overcome this difficulty, a fresh supply of gas must be supplied at certain intervals to the tube interior in response to the decrease in the gas pressure.

A conventional apparatus employed for this purpose consists of a gas container and two electromagnetic valves installed in a tube connecting the container and the laser tube so that the gas confined in the tube lying between the two valves may be fed to the laser tube by the alternate opening and closing of these valves.

This gas-refilling apparatus has significant drawbacks not only because it requires a relatively complex mechanism, but

also because the tube is easily damaged or broken during the manufacturing process, or during shipment because of the use of the heavy electromagnetic valves.

It is an object of the invention to provide a gas tube equipped with a simplified and inexpensive means for gas refilling.

It is a further object of the invention to provide a gas refilling unit for a gas tube in which gas may be supplied to the tube in an accurately controlled manner to maintain a desired gas pressure within the tube.

According to this invention a gas tube is equipped with a gas refilling unit which is comprised of a main gas container, an intermediate gas reservoir, a chamber directly connected to the interior of a gas-filled tube, and valve means lying between the intermediate gas reservoir and the chamber. The main container communicates with the reservoir through a thin tube of an extremely small orifice or passageway, such as a pinhole formed in a metal plate. This tube establishes an extremely restricted flow rate of gas from the main. container to the reservoir.

The valve means may be, as herein specifically described, in the form of a tapered outlet pipe projecting downward into a recessed portion of the chamber and constituting a part of the inten'nediate reservoir. A low-melting-point metal or the like is placed in and fills part of the recessed portion sufficient to reach the tip of the tapered pipe. Means are provided to melt the metal into a liquid state whenever it is desired to release the gas contained in the reservoir into the chamber. When it is in the solid state, the metal restricts the gas within the reservoir and, at the same time, serves as a part of the tube envelope.

When the metal is melted, only the gas that is contained in the intermediate reservoir is released under the gas pressure of the main container to the interior of the tube. The gas in the main container does not reach the tube at this stage, due to the extremely thin orifice linking the main container and the intermediate reservoir. Thus, a substantially predetermined quantity of gas is released for refilling every time the valve is heated and the metal is melted. v

To the accomplishment of the above and to such further objects as may hereinafter appear, the present invention relates to a gas filled discharge tube with gas-refilling means substantially as defined in the appended claims, and as described in the following specification taken together with the accompanying drawing in which:

FIG. 1 is a perspective view of a gas tube for use in a laser; and

HO. 2 is a longitudinal cross sectional view of the gas refilling unit of the invention for use with the tube of FIG. 1.

Referring to H0. 1, a gas laser tube 1 is equipped with a gas refilling unit2 of the invention, the latter serving to replenish the supply of gas (e.g., argon) in the former whenever necessary to maintain a sufficient gas pressure therein. The refilling unit 2 may be connected by a pipe section 10 to a suitable portion of the sidewall of either end of gas laser tube 1. Both unit 2 and pipe section 10 are placed away from the laser light path in the tube 1. v

The gas-refilling unit 2, as shown in greater detail in FIG. 2, includes a main gas container 3 and an intermediate reservoir 8. A tube 4 having an extremely fine orifice or passageway effects communication between container 3 and reservoir 8 and controls the flow rate of gas therebetween. A gas outlet pipe 5 having a tapered'end is provided at one end of intermediate reservoir 8 and protrudes into a recessed portion of a chamber 9,which in turn communicates at its upper end with the lower end of pipe section 10 and thus with the envelope of tube 1. A low-melting-point metal 6 such as indium is placed within and substantially fills the recessed portion of chamber 9, and a heater coil 7 energized by a'power supply 11 surrounds the recessed portion and the metal.

In its solid state, metal 6 forms a hermetic seal for pipe 5 and thus for tube 1. However, when metal 6 is warmed up by the operation of heater 7 to a temperature of say 157 C. (melting point of indium), the gas-filling reservoir 8 is released through pipe 5 and the melted metal into chamber 9. Stated more specifically, the main container 3 is maintained at a pressure of several ten to several hundred torr. With the metal 6 in the melted state, the gas contained in the reservoir 8 passes through the melted metal and overcomes the weight or gravitational pressure plus the surface tension of the melted metal thereof. As soon as the gas pressure in reservoir 8 is decreased to a predetermined value less than the gravitational pressure of the melted metal lying from the surface to the tip of outlet pipe 5, the gas flow is stopped. Reservoir 8 is then refilled with fresh gas from container 3 through the orifice in tube 4.

If the gravitational pressure of the melted metal remains unchanged, the critical pressure at which gas is allowed to pass therethrough depends mainly on the surface tension of the melted indium. Although the surface tension of the indium varies with the orifice diameter of outlet pipe 5, the physical configuration of the orifice, and the wettability between the melted indium and the pipe material, it is roughly in inverse proportion to the orifice diameter of pipe 5. ln other words, the gas pressure at which gas starts penetrating the melted metal is determined by the orifice diameter of the outlet pipe As will be apparent from the foregoing description, the gasrefilling process iscarried out intermittently. Since the amount of gas introduced into chamber 9 in one refilling operation can be kept almost constant, the totaL amount of gas for the recovery of the rated gas pressure at one time is determined by the number of refilling operations to be repeated.

Furthermore, the amount of gas corresponding to a single refilling operation can be determined by suitably designing the volume of intermediate reservoir 8 and the orifice diameter of outlet pipe 5. The time interval between two successive refilling strokes can be controlled by suitably determining the gas pressure in main container 3 and the diameter of the orifice of tube 4.

Experiments carried out on the system of the invention have shown that the amount of argon gas corresponding to one refilling stroke and the time interval between two successive refilling strokes were respectively about 40 cubic centimeters torr, and 20 seconds. In the performance of these tests on the system, the pressure in gas container 3 was torr; the diameter of the orifice of tube 4 was 30 microns; the volume of intermediate gas reservoir 8 was 25 cc.; and the orifice diameter of gas outlet pipe 5 was 2 millimeters. It is to be understood that these values are given only for purposes of example and are in no way intended to limit the scope of the invention.

The electric heater 7 for the indium can be manually controlled by observing pressure reading at a gauge (not shown) for detecting the gas pressure. Alternatively, the electric heater may be turned on" and off automatically by applying a control signal derived from a pressure gauge to the heater.

In the embodiment, the tube 4 of small orifice is employed as a means for moderating the flow of gas from container 3 into reservoir 8. This small orifice may be a pinhole formed in a thin plate to replace tube 4. Moreover, the low-meltingpoint metal 6 may be other than indium. Tin or any other suitable substance of low-melting point may be employed for the same purpose.

It would also be understood that the gas-refilling means of the present invention is applicable not only to a laser discharge tube but to a general gas-filled discharge tube.

The gas-refilling means of this invention can be made compact, light, inexpensive, and easy to handle, because the entire structure can be made of glass.

Thus while only a single embodiment of the present invention has been herein specifically described it will be apparent that modifications may be therein without departing from the spirit and the scope of the invention.

1 claim:

1. A gas-filled discharge tube of the type having a gas-filled chamber requiring gas refilling at predetermined time intervals, and a gas-refilling unit, said gas-refilling unit comprising a container for containing gas at a predetermined pressure, an

intermediate reservoir in fluid communication with said container for allowing a limited flow rate of said gas, said intermediate reservoir having an outlet portion, means for restricting the flow of gas from said container to said reservoir, said flow restricting means comprising a tube section for providing a narrow passageway interposed between said container and said reservoir, the length and the cross-sectional area of said passageway being sufficient to cause at least a temporary difference in pressure between said container and said reservoir when the outlet portion of said reservoir is opened, valve means interposed between said reservoir and said chamber and comprising a recess portion provided in a part of said chamber receiving said outlet portion, a quantity of meltable metal disposed between said recess portion and the open end of said outlet portion, and means for varying the temperature of said metal to thereby alter said metal from a solid to a liquid state, said gas contained in said reservoir passing through the melted metal and overcoming the gravitational pressure plus the surfacetension thereof in its melted state, said gas flow from said reservoir to said chamber being automatically stopped as soon as the gas pressure in said reservoir is decreased to a predetermined value less than the gravitational pressure of the melted metal.

2. The combination of claim 1, in which said meltable material is a low-melting point metal selected from the group consisting of indium and tin.

Claims

1. A gas-filled discharge tube of the type having a gas-filled chamber requiring gas refilling at predetermined time intervals, and a gas-refilling unit, said gas-refilling unit comprising a container for containing gas at a predetermined pressure, an intermediate reservoir in fluid communication with said container for allowing a limited flow rate of said gas, said intermediate reservoir having an outlet portion, means for restricting the flow of gas from said container to said reservoir, said flow restricting means comprising a tube section for providing a narrow passageway interposed between said container and said reservoir, the length and the cross-sectional area of said passageway being sufficient to cause at least a temporary difference in pressure between said container and said reservoir when the outlet portion of said reservoir is opened, valve means interposed between said reservoir and said chamber and comprising a recess portion provided in a part of said chamber receiving said outlet portion, a quantity of meltable metal disposed between said recess portion and the open end of said outlet portion, and means for varying the temperature of said metal to thereby alter said metal from a solid to a liquid state, said gas contained in said reservoir passing through the melted metal and overcoming the gravitational pressure plus the surface tension thereof in its melted state, said gas flow from said reservoir to said chamber being automatically stopped as soon as the gas pressure in said reservoir is decreased to a predetermined value less than the gravitational pressure of the melted metal.