US3428860A

US3428860A - Ablating lamp with improved gas evolving apparatus

Info

Publication number: US3428860A
Application number: US589454A
Authority: US
Inventors: Frithjof N Mastrup
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1966-10-25
Filing date: 1966-10-25
Publication date: 1969-02-18
Anticipated expiration: 1986-02-18

Description

F'. N. MASTRUP Filed Oct. 25, 1966 ABLATING LAMP WITH IMPROVED GAS EVOLVING APPARATUS Feb. 18, 1969 592m om Fri'rhjof N. Mostrup,

INVENTOR.

AGENT.

United States Patent() Ohio Filed Oct. 25, 1966, Ser. No. 589,454 U.S. Cl. 315-111 Int. Cl. H011' 7/24 9 Claims ABSTRACT F THE DISCLOSURE An ablating lamp having a pair of spaced anode and cathode electrodes with a passage extending from one of the electrodes to the other having Wall portions of electrical insulating and conducting materials, the insulating material being electric discharge arc responsive for releasing gas under pressure emitting radiation substantially corresponding to that of a black body having a temperature of the order of at least 20,000 K. when subjected to electrical discharge arcs between the electrodes through the passage. An electric circuit is provided for periodically applying electrical potential energy between the electrodes to develop a voltage drop and electrical discharge arcs therebetween within the passage. Gas evacuation apparatus is provided for providing a pressure substantially lower than atmospheric in the passage prior to each successive electrical discharge arc generated.

This invention relates generally to improvements in ablating discharge lamp apparatus, and in particular relates to improved gas evolving apparatus for use with ablating lamps having great mechanical strength, and providing internal gas pressure and electrical discharge arc control for the lamps.

In ablating lamps of the type revealed in copending U.S. patent applications, Ser. No. 325,084, filed Nov. 20, 1963, now U.S. Patent No. 3,274,437, and Ser. No. 327,- 388, led Dec. 2, 1963, now U.S. Patent No. 3,387,227, generally there is provided an arc discharge passage between an inner cylindrical transparent member and a hollow outer member fashioned entirely from gas ablating dielectric material such as Plexiglas for evolving gas. Energizing potential is applied longitudinally across the passage by means of electrode members disposed at opposite ends of the arc discharge passage. However, when ablating lamps of the type revealed in the hereinbefore mentioned patent applications are subjected to very large electrical power input across the electrodes a disadvantage which arises to limit usefulness of such lamps is that excessive uncontrolled evolution of gas from the outer gas ablating dielectric member produces large peak gas pressures within the passage which contribute to the ultimate destruction of the outer member and the lamps.

Briefly, in accordance with this invention there is provided for ablating lamps improved novel segmented metal and dielectric outer member construction defining the electrical discharge passage which eliminates the disadvantages of prior devices, such as the lamps revealed in the above-referred to patent applications, and provides added advantages. The metal segments of the segmented outer body construction contribute to the apparatus the mechanical strength characteristic of metals. The insulating or ablative dielectric material segments which separate the metal segments fullill a multiplicity of purposes. They serve primarily as distributed sources of carrier gas and the means for peak gas pressure control during electrical arc discharge. In addition they provide electrical insulation lfor the metal segments from each other thus preventing electrical short circuiting within the annular arc discharge passage.

Patented Feb. I8, 1969 ICC In the drawings:

FIG. l is a cross-sectional elevation showing of ablating lamp apparatus incorporating the novel gas evolving apparatus of the present invention; and

FIG. 2 is an enlarged perspective showing of a portion of the lamp apparatus of FIG. 1 showing details of the gas evloving apparatus.

Referring to FIG. l wherein there is shown apparatus in accordance with the present invention as comprising the ablating lamp generally designated by the numeral 10, and electrical circuit arrangement 14 capable of supplying electrical energy to the lamp.

In greater particularity the lamp 10 includes a mounting flange 16. Preferably the mounting flange 16 has a circular aperture 18 therethrough and on its outer surface, coaxial with the aperture 18, a cylindrical, internallythreaded collar 20.

A metallic electrode or cathode 22, preferably a substantially tubular member, has one end 24, and another end 26 with a circular flange portion 28 intermediate the ends. The end 24 is adapted for positioning within the aperture 18 and the flange portion 28 lits within the collar 20 adjacent the ilange 16.

An elongated metallic sleeve 30 has one internally threaded end 32 and another externally threaded end 34 which is adapted to engage the threads of the collar 20 to secure the tlange portion 28 of the electrode 22 therebetween. In addition, the sleeve 30 serves as the external wall of the lamp and provides added strength to the lamp, since pressures developed therein are of considerable magnitude. A. flange 33 is positioned on the sleeve 30, as by welding, and is preferably grounded at 35 to serve along with the electrode 22 and sleeve 30 as a discharge current return path to the electrical circuit 14, as will hereinafter be more clearly apparent.

An elongated tubular member 36, preferably fashioned from Fiberglas, or the like, has an outer diameter such that it closely conforms to the inner diameter of the sleeve member 30 to provide a close fit therebetween and is positioned within the sleeve 30 with one end in abutment with the ange portion 28 of the electrode 22.

A segmented construction, best shown in FIG. 2, consisting of a tubular stack of alternate insulating and conducting material cylinders or

rings

38 and 40 of length L is provided within the tubular member 36 to effect the outer wall of an annular discharge passage 44 of the lamp. In accordance with this invention the insulating material cylinders 38 are formed of a material which is capable of evolving large quantities of gas in the presence of an electrical arc discharge. Materials such as Plexiglas, nylon, polyethylene, and Teflon are suitable for the cylinder 38. Plexiglas has been used with great success. It should be appreciated that a wide variety of materials could be used for the cylinder 38 and that the present invention is not limited to the specific materials referred to above. The cylinders 40 are preferably fashioned from `stainless steel, but could also be graphite, or an alloy such as Mallory 1000.

At the righthand end of the insulating tube 36 there is inserted a second electrode or anode 46. The electrode 46 is preferably provided with a first tubular end portion 48 having an outer diameter such as to closely tit the tube 36, a. second reduced diameter tubular end portion 50, an intermediate outer shoulder 52, and an inner shoulder 54. The electrode 46 like the first electrode 22, is preferably fashioned from stainless steel, but could be either graphite or Mallory 1000, and is electrically connected to the circuit 14.

An end member 56, fashioned from insulating material, has one tubular end portion 58 which ts over the portion `48 of the electrode 46, and a second externally threaded end portion 60 of reduced inner diameter which forms an inner shoulder 62 adapted to abut the shoulder 52. Thus, when the outer threads of end member 56 are engaged with the internal threads of sleeve end 32 and is screwed therein, the insulating and conducting

cylinders

38 and 40 are tightly compressed between the ends of

electrodes

22 and 46.

The electrode 46 is connected by means of a suitable electrical line 64 to the circuit 14 capable of discharging electrical energy up to 33,000 joules into the lamp structure within less than 20 microseconds. To this end the high voltage circuit 14 can be of the type revealed in the above-mentioned patent application, Ser. No. 325,084 tiled Nov. 20, 1963. Briefly, the circuit 14 includes a high potential direct current source 66 capable of supplying potentials from about kv. up to 30 kv. with the high voltage output terminal being connected through a current limiting resistor 68 to a high voltage storage capacitor 42 which has one plate grounded. The other capacitor plate is connected through a conventional ignitron switch 70 by means of the line 64 to the electrode 46. The other terminal of the direct current source 66 is grounded at 35.

On the other side of the ilange 16 there is provided a housing forming a gas ballast volume 72 wherein all gases evolved during electrical discharge exhaust. The housing consists of a generally cylindrical body portion 74 having an end ange portion 76 and a flange portion 78 suitably aflixed to the flange 16 as by bolts 80 and nuts 82. A flange 84 has a circular aperture 86 therethrough in coaxial alignment with the aperture 18 of the flange 16 and a cylindrical, externally threaded collar 8S coaxial with the aperture 86. The housing is preferably adapted to be connected as indicated at 87 to a conventional vacuum pump (not shown) so that pressure within the volume 72 is maintained substantially lower than atmospheric at all times to evacuate the gases formed in passage 44 prior to each successive electrical discharge arc.

A transparent tube 89 is positioned through the

apertures

86 and 18 such that one end abuts against a seal 90 within an annular groove 92 of the shoulder 54 to form the inner wall of the annular discharge region 44. The tube 89 is preferably quartz because of its strength, optical properties and ability to withstand without rapid deterioration or darkening repeated high current discharges in the passage 44. The other end of the tube 89 is embraced by an annular flexible sealing element 94 abutting an internal shoulder 96 formed in the collar 88, a metallic ring 98, another sealing element 100, and another metallic ring 102. A member 104 which is internally threaded is adapted for engagement with the external threads of collar 88. Thus, when the member 104 is screwed on, the collar 88, the

seals

94 and 100 are tightly compressed to form fluid tight seals about the quartz tube 89.

A laser rod 106 which could be a ruby, or the like, is supported within the quartz tube 89 such that it is surrounded by the stacked alternate insulating and

metallic cylinders

38 and 40.

One important feature `of the segmented channel lamp construction of the present invention is that electrical short circuiting of the annular discharge passage 44 can be prevented during generation of electrical discharge arcs between the

electrodes

22 and 46 by satisfying certain initial conditions of segmented channel construction. In this regard it will be appreciated that a generated electrical discharge arc between the

electrodes

22 and 46 can do one of two things in the discharge passage 44. It can either entirely fill the passage 44 or it can short by going from one metallic segment 40 to another. If it be assumed that there is no electrical short circuiting in the passage 44 between the

electrodes

22 and 46 and then the total voltage drop between the electrodes can be given by Vere: Va'l Vc-l- Vpl l) where Va is the anode voltage drop; Vc is the cathode voltage drop; and Vpl is the voltage drop across the plasma in the passage 44. If it now be assumed that electrical short circuiting occurs the total voltage across the annular discharge passage 44 is then given by the exand n is equal to the number of metallic 4segments 40, and a can be approximated by the expression where h1 is the axial length of a single cylindrical element 38; and L is the axial length of the tubular stack of

rings

38 and 40 dening the outer wall of passage 44. It has been found that a may vary from about .1 to about .5 in devices constructed in accordance with this invention.

Comparing Equations 1 and 2 it can be seen that the expression nWmLVc) (1-)V1.1 0 (4) must be satisfied in order to prevent short circuiting from occurring in the passage 44.

Peak plasma pressure regulation in the passage 44 can be conveniently accomplished in accordance with this invention. It has been determined that peak plasma pressure P developed in the passage 44 is dependent on the relative amounts of ablating and nonablating material surface area exposed to the electrical discharge arc generated between the

electrodes

22 and 46 and is given approximately by the expression where E is the electrical energy content of capacitor 42; V is the volume of passage 44; and h2 is the axial length of a single metallic segment 40.

Operation of the lamp apparatus of FIGS. 1 and 2 is substantially as follows: Upon application of a voltage in the range of about 5 kv. up to 30 kv. to the electrodes from the capacitor, discharge through the passageway is initiated by a sliding spark along the wall lof the passageway between the electrodes. The sliding spark along the inside wall of the segmented construction decomposes rst a minute amount of the wall material of segments and releases a small amount of the gas into the passageway where the gas is contained long enough to serve as a carrier of a powerful gas discharge arc Ibetween the electrodes. The powerful discharge of electrical energy in the passage 44 results in evolution of additional quantities of gas from the ablating wall surfaces of segments 38 so that substantially instantaneously enough gas is released to provide an instantaneous peak pressure in excess of one atmosphere in the passage 44. This rapid pressurization and simultaneous dissipation of large quantities of electrical energy produces a high pressure high temperature plasma. The plasma thus produced gives rise to a powerful pulse of vacuum ultraviolet, ultraviolet, visible, and infrared radiation within the passage 44 which corresponds to a black body radiator having a temperature on the order of 20,000 K. and is utilized for optically pumping the ruby rod positioned within the transparent member to geenrate coherent radiation.

While I have described and illustrated a speciic embodiment of my invention, it will be clear that variations of the details of construction which -are specifically illustrated and described may be made without departing from the true spirit and scope of the invention yas dened in the `appended claims.

What I claim is:

1. In combination comprising:

a pair of spaced anode and cathode electrodes;

means dening a passage and extending from one of said electrodes to the other, said passage having wall portions of electric insulating and conducting materials, said insulating material being electric discharge arc responsive for releasing gas under pressure emitting r-adiation substantially corresponding to that of a black body having a temperature of the order of at least 20,000 K. when subjected to electrical discharge arcs between said electrodes through said passage;

electric circuit means for periodically applying electrical potential energy between said electrodes to develop a voltage drop and electrical discharge arcs therebetween within said passage; and

evacuating means -for providing a pressure substantially lower than atmospheric in said passage prior to each successive electrical discharge arc.

2. The combination as set forth in claim 1 wherein said passage defining means comprises concentric tubular members defining said passage therebetween.

3. The combination as set forth in claim 2 wherein one of said tubular members comprises a series of alternate electric insulating and conducting material rings defining said wall portions.

4. The combination as set forth in claim 3 wherein said one tubular member is the outer one of said concentric tubular members.

5. The combination as set forth in claim 2 wherein one of said tubular members is light transparent.

6. The combination as set forth in claim 5 wherein said one tubular member is the inner one of said concentric tubular members.

7. The combination as set forth in claim 3 wherein said pressure is approximately defined in accordance with the expression where P is said pressure; E is said energy; V is the volume Of said passage; n is the number of said conducting rings; h1 is the axial length of one of said insulating rings; and h2 is the axial length of one of said conducting lrings.

8. The combination as set forth in claim 3 wherein said electrical discharge arcs are deined in accordance with the expression where n is the number of said conducting rings; Va is the anode electrode voltage drop between said electrodes; Vc is the cathode electrode voltage `drop between said electrodes; a is a quantity that m-ay have a magnitude of from about .1 to about .5; and Vpl s the voltage drop across `said gas.

JAMES W. LAWRENCE, Primary Examiner.

R. F. HOSSFELD, Assistant Examiner.

9. In combination comprising:

a pair of spaced anode and cathode electrodes;

a light transparent tubular member;

a tubular member of alternate electric insulating and conducting material rings extending between said electrodes and surrounding said light transparent tubular member in concentric relationship therewith to define a passage therebetween, said insulating material rings being electric discharge arc responsive -for releasing gas under pressure emitting radiation substantially corresponding to that of `a black body having a temperature of the order of -at least 20,000 K. when subjected toelectrical discharge arcs between said electrodes through said passage;

means for evacuating said gas from said passage prior to each successive electrical discharge arc;

said pressure lbeing approximately dened in accordance with the expression and said electrical discharge arcs being delined in accordance with the expression where P is said pressure; E is said energy; n is the number of said conducting material rings; h1 is the axial length of `one of said insulating material rings; h2 is the axial length of one of said conducting material rings; Va is the anode electrode voltage drop between said electrodes; Vc is the cathode electrode voltage drop between said electrodes; is a quantity having a magnitude of lfrom about .1 to about .5 and Vpl is the voltage drop across said gas.

References Cited UNITED STATES PATENTS 8/1936 Torok 313-231 X U.S. Cl. X.R.