Nonconsumable metal electric arc electrodes are described capable of being operated in a variety of gases at various pressures, current, and powers. The cathode has a circular annulus tip to spread the emission area for improved cooling

Decker, A. J.

Gettelman, C. C.

Goldman, G. C.

Hall, J. H.

Pollack, J. L.

English

NASA Technical Reports Server

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON. D.c. 20546
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YoTF° GP
TO:
FROM:
PEC 2 7 1973
KSl/Scientific & Technical Information Division
Attention: Miss Winnie M. Morgan
GP/Office of Assistant General Counsel for
Patent Matters
SUBJECT: Announcement of NASA-Owned U.S. Patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. patent is beinc
forwarded for abstracting and announcement in NASA STAR.
The following information is provided:
U.S. Patent No.
Government or
Corporate Employee
Supplementary Corporate
Source (if applicable)
NASA Patent case No.
employee of a NASA Contractor, the following is applicable:
Yes / / No /.K /
Pursuant to Section 305(a) of the National Aeronautics and
Space Act, the name of the Administrator of NASA appears on
the first page of the patent; however, the name of the actual
inventor (author) appears at the heading of column No. 1 of
the Specification, following the words ". . , with respect to
an invention of ..."
Elizabeth A. Carter
Enclosure
Copy of patent cited above
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United States Patent
HaJl et al.
nij 3,777,200
[45j Dec. 4, 1973
134 ] HIGH POWERED ARC ELECTRODES
[751 Inventors: Jesse H. Hall, Fairview Park;
Clarence C. Gettelman, Westlake;
John L. Pollack, North Olmsted, all
of Ohio; Gary C. Goldman, Ann
Arbor, Mich.; Arthur J. Decker,
Lake wood, Ohio
[73] Assignee: The United States of America as
represented by the Administrator of
the National Aeronautics and Space
Administration, Washington, D.C.
122] Fifed: May 14, 1971
[21] Appl. No.. 143,508
[52] U.S. Cl 313/32, 313/153, 313/209,
313/217,313/224
[51] Int. CI HOlj 17/04
[58] Field of Search 313/30, 32, 37, 209,
313/211,217, 184,224, 341
[56] References Cited
UNITED STATES PATENTS
3,073,984 1/1963 Eschenbach et al 313/30
1,055,003 3/1913 Wagener 313/32
2,239,416 4/1941 Ehrenberg 313/37
2,887,603 5/1959 Haidinger 313/211
2,179,929 11/1939 Hansell 313/30
3,405,305 10/1968 Winzeler et al 313/30
3,474,278 10/1969 Thouret et al 313/30
3,531,673 9/1970 Paquette 313/32
Primary Examiner—Roy Lake
Assistant Examiner—Darwin R. Hostetter
Attorney—N. T. Musial, G. E. Shook and J. R.
Manning
[57] ABSTRACT
Nonconsumable metal electric arc electrodes capable
of being operated in a variety of gases at various pres-
sures, current, and powers. The cathode has'.- ~:- -ular
annulus tip to spread the emission are? -ved
cooling.
13 Claims, 8 Draws-v . » • • - -
PATENTED OEC 41973 3,777,200
SHEET 1 OF 4
o
(Z
BY
INVENTORS
JESSE H. HALL
CLARENCE C. GETTELMAN
JOHN L. POLLACK
GARY C. GOLDMAN
RTHUR J. DECKER
ATTORNEYS
PATENTED DEC 413/3
SHEET 2 OF 4
3.777,200
36
FIG. 2
/-60
FIG. 3
BY
INVENTORS
JESSE H: HALL
CLARENCE C. GETTELMAN
JOHN L. POLLACK
GARY C. GOLDMAN
RTHUR J. DECKER
PATENTED DEC 41973 3,777,200
SHEET 3 OF 4
FIG. 4 FIG. 5
FIG. 6
BY
INVENTORS
JESSE H. HALL
CLARENCE C. GETTELMAN
JOHN L. POLLACK
GARY C. GOLDMAN
ABTHUR J. DECKER
A T T O R N E Y S
PATENTED OEC 3,777,200
10
SHEET U OF 4
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3,777,200
HIGH POWERED ARC ELECTRODES
ORIGIN OF THE INVENTION
The invention described herein was made by employ-
ees of the United States Government and may be man- 5
ufactured and used by or for the Government for gov-
ernmental purposes without the payment of any royal-
ties thereon or therefor.
BACKGROUND OF THE INVENTION 10
This invention is concerned with a high power, free-
burning electric arc which forms the radiation source
for a solar simulator. The invention is particularly di-
rected to improved electrodes capable of extended life
and clean operation. •
Various types of electrodes are used to produce elec-
tric arcs. Consumable carbon electrodes are used with
many types of arcs. Compact arc lamps which utilize
less than 20 kilowatts employ radiation cooled, non-
 2Q
consumable metal electrodes. Compact arc lamps in
the 20 to 40 kilowatt range employ water cooled metal
nonconsumable electrodes. Still higher power lamps
greater than 50 kilowatts have similar electrodes in ad-
dition to a moving gas which provide useful lives of sev- 25
era! hours.
Some electrodes have short lives while others are not
economical to operate. The consumable electrodes re-
quire periodic replacement. Only a limited amount of
illumination can be expected from some low powered 30
lamps.
A solar simulator uses an arc as the radiation source.
This arc must be positioned precisely and maintained
stable with respect to an optical collector. Electrodes
for the arc must be capable of high power operation. 35
Evaporation of the electrodes must be small to mini-
mize the deposition of electrode material on optical
surfaces.
SUMMARY OF THE INVENTION 40
These problems have been solved by using noncon-
sumable metal electric arc electrodes in accordance
with the present invention. The anode contains a num-
ber of small diameter passages for carrying a liquid
 45
coolant at high flow velocities. The cathode is likewise
liquid cooled and its structure reduces the local heat
load which must be conducted through the tip to the
cooling liquid. A circular annulus tip on the cathode
spreads the emission area from a concentrated spot to so
a continuous or intermittent line. The emission from all
portions of this line occurs simultaneously.
OBJECTS OF THE INVENTION
It is, therefore, an object of the present invention to 55
provide nonconsumable electrodes that are capable of
being operated at high power.
Another object of the invention is to provide noncon-
sumable metal electric arc electrodes having longer
lives for use in a solar simulator. 60
A further object of the invention is to provide elec-
trodes that are capable of being scaled for the most effi-
cient operation under various conditions.
These and other objects of the invention will be ap-
parent from the specification that follows and from the
drawing wherein like numerals are used throughout to
identify like parts.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of a portion of a solar sim-
ulator constructed in accordance with the present in-
vention;
FIG. 2 is an enlarged vertical section view of an
anode utilized in the apparatus shown in FIG. 1;
FIG. 3 is an enlarged vertical section view of a cath-
ode utilized in the apparatus shown in FIG. 1;
FIG. 4 is an enlarged vertical section view of an alter-
nate embodiment of the cathode shown in FIG. 3 which
includes apparatus for generating a magnetic field;
FIG. 5 is an enlarged vertical section view of an alter-
nate embodiment of the cathode as shown in FIG. 3
having an annulus with a raised center point;
FIG. 6 is an enlarged vertical section view of an alter-
nate embodiment of the cathode shown in FIG. 3 hav-
ing a provision for the admission of a cooling gas to the
center of the arc;
FIG. 7 is an enlarged vertical section view of an alter-
nate embodiment of the anode shown in FIG. 2; and
FIG. 8 is an enlarged quarter section view of still an-
other alternate embodiment of the anode utilized in the
apparatus shown in FIG. 1.
DESCRIPTION OF THE PREFERRED
EMBODIMENT
Referring now to the drawing there is shown in FIG.
1 a pair of electrodes constructed in accordance with
the present invention. These electrodes are used to
form the arc of a solar simulator.
Each electrode pair comprises an anode 10 and a
cathode 12 positioned in a housing 14 that is filled with
a suitable inert gas, such as argon, krypton, or xenon.
The anode 10 is rigidly mounted to a base 16. The cath-
ode 12 is supported by suitable mechanism 18 for re-
ciprocable movement toward and away from the anode
10. The mechanism 18 enables the cathode 12 to be
moved into contact with the anode 10 to initiate an arc
by the passage of a short circuit current through the
electrodes. The mechanism 18 further enables the
cathode 12 to be separated from the anode 10 a prede-
termined distance when the current is increased to the
operating value.
The anode 10 has a cylindrical body 20 of high con-
ductivity copper. It is also contemplated that the anode
10 can be fabricated from refractory metals, such as
tungsten and molybdenum, or from alloys of these met-
als.
As shown in FIG. 2 an end surface 22 of the body 20
which is directed towards the cathode 12 is slightly
concave. The surface 22 is smooth to avoid constric-
tion of the arc attachment. A plurality of parallel con-
duits 24 are adjacent to the surface 22. The conduits 24
are in communication with an intake manifold 26 and
exhaust manifold 28. Each of these manifolds extends
about approximately one-half the periphery of the body
20.
Supply passages 30 extend along one side of the body
20 parallel to the axis of the anode 10. One end of each
supply passage 30 is in communication with the intake
manifold 26 while the opposite end is connected to a
suitable coolant source 32 such as water pressurized to
about 1000 psi through a supply line 34.
Discharge passages 36 extend along the opposite side
of the body 20 as shown in FIG. 2. One end of each dis-
charge passage 36 is in communication with the ex-
3,777,200
4
haust manifold 28 while the opposite end is in commu-
nication with a suitable coolant cooling device 38
through an exhaust line 40 as shown in FIG. 1.
Each cooling conduit 24 preferably has a small diam-
eter on the order of about one-fourth inch or less. It is 5
contemplated that internal rifling may be utilized to in-
crease the heat transfer through a thin wall structure.
Conduits 24 in the form of tubes having thin walls capa-
ble of withstanding high internal coolant pressures have
been successfully used: A high pressure is necessary to 10
raise the saturation temperature of the cooling liquid
and to cause high flow velocities which is the require-
ment for high heat transfer:
The cathode 12 has a cylindrical body 42 which sup-
ports a cap 44 as shown in FIG. 3. The body 42 is pref- 15
erably copper while the cap 44 is thoriated tungsten.
The copper body 42 is vacuum cast directly to the tho-
riated tungsten cap 44. This eliminates the customary
uncertainties encountered when making an indirect
bond. 20
A tube 46 extends along the axis of the cylindrical
body 42 toward the cap 44. A flow divider 48 is
mounted on the end of the tube 46. The opposite end
of the tube 46 is placed in communication with the
coolant source 32 through a supply line 50 as shown in 25
FIG. 1.
The coolant passes through the tube 46 toward the
cap 44 and strikes a fin 52 in the center of the body 42.
This serves to divide the flow of coolant through a con-
stant area channel 54 adjacent the cap 44. The coolant 30
then passes through an annular passage 56 where it
flows into a discharge line 58 connected to the cooling
device 38. The coolant flow passages inside the cath-
ode 12 are plated with a less chemically active metal,
such as gold, to resist deposits from the coolant thereby 35
reducing the problem of low thermal conductivity re-
sulting from such deposits.
The curved water passage 54 and central fin 52 re-
duce the local heat load to the coolant by increasing
the area, over which the cathode heat load enters the 40
coolant. The constant cross sectional area of the pas-
sage 54 ensures a high heat transfer coefficient over the
entire cathode cooling surface.
An important feature of the invention is the provision
of a v-shaped crater 60 in the cap 44. The crater 60 ere-
ates an annular cathode from the molten annulus which
forms near the rim of the crater 60 when the arc is run-
ning.
In operation, the cathode 12 is moved into contact
with the anode 10 by the mounting mechanism 18. An
arc is struck by passing a short circuit current of about
350 amperes through the electrodes. This current is
supplied by two direct current generators 62 and 64
connected to a continuously variable voltage control
66. The generators 62 and 64 have the capacity of sup-
plying from 0 to 500 volts. A ballast resistor 68 is con-
nected in series with the electrodes.
After the arc is struck, the cathode 12 is separated
from the anode 10 for a distance of about 3 inches. The
arc spreads over the crater 60 and forms a molten an-
nulus near the rim. The area of attachment of the arc
to the cathode 12 is larger than on conventional cath-
ode tips. This larger area of attachment reduces the
local heat load.
The emission from the cathode 12 can spread along
the rim of the crater 60 before design operating power
is reached. Emission increases strongly with increasing
60
65
temperature. The rim of the crater 60 is the least
cooled part of the cap 44 causing simultaneous emis-
sion to occur from a ring or line near the rim.
The local heat load limits the current density and
electrical power at which an electrode operates effec-
tively. Effective operation is operation without exces-
sive boiling off or melting of the emitting material, or '
boiling burnout occurring on the water cooled side. If
the requirements exceed the effective operating condi-
tion for one electrode then multiple electrodes operat-
ing in parallel must be employed. This annular configu-
ration is analogous with multiple electrodes in the form
of an infinite number of cathodes arranged in a circle.
Electrodes constructed in accordance with the inven-
tion have been operated for 40 hours between 200 kilo-
watts and 400 kilowatts in argon. The average pressure
of the arc ranged between 2 and 8 atmosphere. The
current ranged between 2,600 amperes and 4,000 am-
peres.
DESCRIPTION OF ALTERNATE EMBODIMENTS
Referring now to FIG. 4 there is shown an alternate
embodiment of a cathode utilized in the apparatus
shown in FIG. 1. This cathode has a flow divider 70
mounted on the centrally disposed tube 46. The config-
uration of the flow divider 70 is the same as that of the
flow divider 48 as shown in FIG. 3.
A direct current magnetic field generating device 72
is contained in the flow divider 70. The magnetic field
generating device 72 controls the rotation of the spot
arc emission about the tip of the annulus 60.
It is contemplated that a similar rotating magnetic
field producing device can be mounted inside the hol-
low anode. In this embodiment the arc attachment area
is rotated to reduce the dwell of the arc foot and the
local heat load on the anode.
The cathode shown in^the embodiment of FIG. 5 uti-
lizes a cap 74 having an annulus 76 with a raised center
point 78. This embodiment combines line and spot
emission.
The cathode shown in FIG. 6 has a cap 80 with a cra-
ter or annulus 82. An opening 84 is provided in the cen-
ter of the crater 82. A passage 86 has one end in com-
munication with the opening 84 and the opposite end
connected to a source of inert cooling gas. In this em-
bodiment the inert gas is injected into the center of the
arc through the center of the annulus.
While the preferred embodiment as well as several
alternate embodiments of the invention have been
shown and described, it is contemplated that other
structural modifications may be made without depart-
ing from the spirit of the invention or scope of the sub-
joined claims. By way of example it is contemplated
that the end surface 22 of the anode 10 may be flat as
shown in FIG. 7 or convex as shown in FIG. 8 as well
as concave.
What is claimed is:
1. Apparatus for producing an arc for a radiation
source in a solar simulator comprising,
a rigidly mounted copper anode having an outwardly
directed end surface,
a copper cathode mounted for reciprocal movement
toward and away from said anode for initiating and
adjusting the arc,
a housing enclosing said anode and said cathode, said
housing being filled with an inert gas,
3,777,200
means for passing an electric current through said
anode and cathode to maintain said arc, and
a thoriated tungsten cap bonded to the end of said
cathode, said cap having a crater facing the end
surface of said anode for forming an annulus 5
whereby the emission area of said cathode is spread
from a concentrated spot to a line with emission
from all portions of said line occurring simulta-
neously.
2. Apparatus as claimed in claim 1 including a raised to
central portion within the annulus.
3. Apparatus as claimed in claim 1 wherein a housing
is filled with an inert gas as selected from the group
consisting of argon, xenon and krypton.
4. Apparatus as claimed in claim 1 including first is
cooling means for removing heat from the anode, and
second cooling means for removing heat from the
cathode.
5. Apparatus as claimed in claim 4 including a source
of water under pressure connected to said first cooling 20
means and said second cooling means for removing
heat from said anode and said cathode.
6. Apparatus as claimed in claim 5 wherein said first
cooling means includes
a plurality of parallel conduits in said anode, and 25
means, for supplying water under pressure from said
source to said parallel conduits, and
said second cooling means includes
a plurality of passages in said cathode, and
means for supplying water under pressure from said
source to said passages.
7. Apparatus as claimed in claim 6 wherein the water
from said source is under pressure from about 1,000
psi.
8. Apparatus as claimed in claim 6 wherein the pas-
sages in said cathode are gold plated to resist deposits
from the pressurized water.
9. Apparatus as claimed in claim 1 including an open-
ing in the center of said annulus, and means for supply-
ing an inert gas to the arc through said opening.
10. Apparatus as claimed in claim 1 including means
for generating a magnetic field in said cathode for con-
trolling the rotation of spot arc emissions around the
annulus.
11. Apparatus as claimed in claim 1 wherein said out-
wardly directed end surface of said anode is concave.
12. Apparatus as claimed in claim 1 wherein said out-
wardly directed end surface of said anode is substan-
tially flat.
13. Apparatus as claimed in claim 1 wherein said out-
wardly directed end surface of said anode is convex.
30
35
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High powered arc electrodes

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