Long arc column gas discharge tube

A low pressure Ultra Violet (UV) light source produces a high intensity output proportional to the inside diameter and length of a arc discharge column. The light source includes a cathode and anode contained within a high density ceramic body and a sapphire window mounted in line with the arc discharge column. The anode is in line with the arc column at the end opposite the sapphire window, and the cathode is disposed to an area outside the arc discharge column to which the arc moves through an aperture in the side of the arc discharge column structure. As the electrons move through the low pressure gas ionization of the gas occurs releasing photons in the UV region of the spectrum. The sum of the photons generated at each location along the arc discharge column produces the high intensity UV radiation that exits the lamp through a sapphire window.

BACKGROUND OF THE INVENTION

The present invention relates to a gas discharge tube, and more particularly to a gas discharge tube of high density material and an arc column producing a high intensity light source for spectroscopy, chromatography, or the like.

Low pressure high intensity arc lamps are typically made of quartz or glass which requires labor intense multiple glass transitions between the light output window and the body of the lamp to compensate for the large difference in thermal expansion between the body material and the window. When the gas within the lamp is Deuterium, such body material is not dense enough to eliminate the slow loss of the gas because of the permeability of the body material to Deuterium. The loss of Deuterium may also occur through window material used in the lamp. In order to extend the useful operational life of the lamp against the slow loss of Deuterium, the lamp wall and window are typically coated with a ceramic or glaze which reduces the gas permeability of the overall structure. The loss of Deuterium may be addressed by including a large amount of Nickel in the internal construction, which Nickel is presaturated with Deuterium prior to sealing the lamp with its final fill pressure. The slow release of Deuterium from the Nickel into the lamp replenishes of the lost Deuterium. Unfortunately, this process is labor intensive, requires many different materials, and uses gas permeable materials requiring special coatings. Additionally, control of the arc ball of currently manufactured Deuterium lamps is difficult and in some cases requires multiple DC sources.

BRIEF SUMMARY OF THE INVENTION

The present invention addresses the above and other needs by providing a gas discharge tube in which favorable stability is provided that has long life while realizing high luminance, and in which a light-emitting portion assembly is integrated into a unitized structure.

The present invention addresses the above and other needs by providing a low pressure Ultra Violet (UV) light source which produces a high intensity output proportional to the inside diameter and length of a first discharge path. The light source includes a cathode and anode contained within a high density ceramic body and a sapphire window mounted in line with the first discharge path. The anode is in line with the first discharge path at the end opposite the sapphire window, and the cathode is disposed to an area outside the first discharge path to which the arc moves through an aperture in the side of the first discharge path structure. The anode includes a target material to receive electrons from the plasma arc. An electric field is applied to the anode and cathode and the cathode includes an element to produce electrons which are accelerated through the first discharge path towards the anode in response to the electric field. As the electrons move through the low pressure gas ionization of the gas occurs releasing photons in the UV region of the spectrum. The sum of the photons generated at each location along the first discharge path produces the high intensity UV radiation which exits the lamp through a sapphire window.

In accordance with one aspect of the invention, a long arc column discharge tube is caused to discharge a predetermined light from a light exit window of a hermetically sealed container toward the outside by scaling gas into the hermetically sealed container, electrically connecting to first and second stem pins disposed in a standing position in a stem which is provided in the hermetically sealed container so as to extend in a tube axis direction, and generating discharge between an anode and a cathode. The gas discharge tube is characterized by: a first discharge path between the anode and cathode; and having an opening of predetermined length and diameter, restricting the arc size, producing high intense light output that is a summation of photons generated over the length of the column.

In accordance with another aspect of the invention, when high luminance light is to be produced, it is not simply a case of changing the diameter of the first discharge path, but also requires changing the length of the arc column, internal gas pressure, and arc current.

In accordance with yet another aspect of the invention, the gas discharge tube is fabricated from high density ceramic which is impermeable to Deuterium or other gas contained therein, and includes a window which is also impermeable to the Deuterium or other gas, and contains a minimum of conductive metal which must be electrically insulated from the gas discharge. Such gas discharge tube may be made of alumina with a window of sapphire, which materials have similar thermal expansions which allows them to easily seal together by means of a fused glass frit or metal braze. The use of a high density ceramic throughout enables all the components therein to be easily bonded together with a sealing method which is impermeable to the Deuterium or other gas without the need for multiple joints of intervening materials of varying thermal expansions.

In accordance with still another aspect of the invention, the gas discharge tube is fabricated with the anode offset from the axis of the first discharge path and the addition of a second sapphire window on axis and opposite the sapphire exit window through which the light from the gas discharge exits the lamp, enabling the addition of an external light source of differing wavelength emissions to be located at the second sapphire window and those wavelength emissions add to that produced in the gas discharge tube yielding multiple wavelength emissions from the sapphire exit window.

DETAILED DESCRIPTION OF THE INVENTION

A long arc column discharge tube10is shown inFIG. 1Aand a bottom view of the long arc column discharge tube10is shown inFIG. 1B. The long arc column discharge tube10includes a ceramic base14, ceramic body12, exit window15, an anode stem16and cathode stems18aand18b, hermetically sealed (i.e., a gas tight container) into a single assembly. A ceramic long column structure20defines a first discharge path22directing the first discharge, a second discharge path24through a side aperture in the ceramic long column structure20, a beam shaping column26, an integral window shield30, an integral cathode stem support32, cathode34, and an anode36. A plasma arc discharge column comprises the first discharge path22and the beam shaping column26. In another embodiment, the window shield is spaced apart from the long column structure20.

Light is emitted by the Deuterium gas by passage of electrical current between the cathode34and anode36through the Deuterium gas, producing a gas discharge whose intensity is enhanced by the length and diameter chosen for the first discharge path22. The second discharge path24allows completion of the discharge between the cathode34, and anode36.

The light exiting the first discharge path22is shaped by the length and diameter of the beam shaping column26, and the diameter of the beam shaping column26may vary from the diameter of the first discharge path22. The diameter of the beam shaping column26thus defines the width of the light pattern exiting the window15.

The exit window shield30is made integral to the long column structure20, for ease of fabrication and to keep the exit window15clear of any foreign material ejected from the cathode34. The exit window shield30may be made from any non-electrically conducting material, and is preferably a ceramic material.

The cathode stem support32, is made integral to the long column structure20, for ease of assembly, support for cathode34, and cathode stems18aand18b.

The long column structure20, is sealed to the base14, so the electric discharge is directed from anode36, through the first discharge path22(plasma arc column), and the second discharge path24, to the cathode34.

The anode36, is joined to the anode stem16, which is sealed through base14, allowing electric current to pass through base14, to the anode36, and can be made of a refractory metal, such as Tungsten, or of any appropriately doped material such as Cerium doped Tungsten. The anode36is shown with a sharp tip to ensure electric arc attachment be at the tip. The cathode34, is joined at two places to cathode stems18aand18b(seeFIG. 3A), allowing electric current to pass through base14, to the cathode34.

The exit window15, is preferably sealed to the body12by means metal braze or glass frit, providing a hermetically sealed joint.

The body12and long column structure20are preferably sealed to base14by means of metal braze or glass frit, providing a hermetically sealed assembly. Positioning of the exit window15, the long column structure20, and the body12to the base14, may be precisely located by means of grooves or shoulders that are made integral to the base14, or the body12.

FIG. 2, shows five different anode configurations and are described as:

a) anode36which is a sharp pointed cone wherein the electric current of the gas discharge attaches directly to the point;

b) anode38, is a truncated cone wherein the flat is dimensioned to match the electric current of the gas discharge;

c) anode40, is a domed cone that enables the electric current of the gas discharge to envelope the dome where it is essential to maintain a lower temperature of the anode;

d) anode42, is a flat disk wherein the electric current of the gas discharge is in contact at the center of the disk; and

e) anode44, is a curved disk (dish shape) having a radius defined by the distance between the end of the long column6first discharge path and the curved disk, enabling the total length of the gas discharge path between the cathode and anode to remain constant independent of the electric current contact point on the anode curved disk.

Any of the anodes ofFIG. 2, can be made of a refractory metal, or one that is doped with a material that enhances release of electrons.

A first alternative embodiment of the long column structure20a, without integral cathode stem supports, is shown inFIG. 3and cross-sectional view of the long column structure20ataken along line3A-3A ofFIG. 3is shown inFIG. 3A. The long column structure20aincludes cathode supports46aand46bto support cathode stems18aand18b. The long column structure20ais otherwise similar to the long column structure20.

A cross-sectional view of the long arc discharge tube showing the beam shaping column defines a first exit angle A1of the light exiting the first discharge path is shown inFIG. 3Band a cross-sectional view of the long arc discharge tube showing a second exit angle A2of light exiting the first discharge path when the diameter of the first discharge path and beam shaping column are identical is shown inFIG. 3C.

A second alternative embodiment of the long column structure20bis shown inFIG. 4. The long arc discharge tube20bdoes not include an integral exit window shield or integral cathode stem support, and has free standing cathode stems18aand18bsupporting the cathode34.

A third alternative embodiment of the long column structure20cis shown inFIG. 5. The long column structure20cincludes a separate exit window shield48installed either by attachment to the long column structure20c, or by separate means.

A fourth alternative embodiment of the long column structure20dis shown inFIG. 6. The long column structure20dincludes the exit window shield30as an integral part of long column structure20d.

A fifth alternative embodiment of the long column structure20eis shown inFIG. 7. When it is required the anode36not be in direct line with the first discharge path22, the long column structure20emay used with anode36horizontally offset from the first discharge path22.

A cross-sectional view of a sixth alternative embodiment of the long column structure20fis shown inFIG. 8. The long column structure20fhas an additional sapphire window50added on axis with the exit window15, but at an opposite end of the long arc column discharge tube residing in the base14. The second sapphire window50may provide an additional light source having different wavelengths. The second sapphire window50enables photon emissions from an external light source to pass through the long column structure20fand exit, along with the light produced by the gas discharge, through the gas discharge tube exit window15.

A cross-sectional view of an alternative embodiment of a window47is shown inFIG. 9. The window47is formed as a lens allowing focusing of the light from the first discharge path22on an external target.

A cross-sectional view of a second alternative embodiment of window54is shown inFIG. 10. The window54has a different thermal expansion than sapphire. Window54is sealed to the body by means of an intervening thermal expansion material52, such that little or no stress is applied to the window54.