Establishing an arc between water-cooled tungsten-tipped electrodes, maintaining the arc along the centerline of a central jet of argon gas, and surrounding the argon jet with a coaxial sheath of nitrogen stabilizes operation of a low-frequency ac electric arc

Lanzo, C. D.

English

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May 1970	 Brief 70-10065 
Ul NASA TECH BRIEF H 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage commercial 
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A Stabilized Low-Frequency Alternating-Current Electric Arc
The problem: and increases the plasma intensity.) Helium was also 
To achieve stable operation of a low-frequency used as the sheath gas, but with helium, the arc was 
(12 to 22Hz) ac el&tric arc, quite unstable and arc startup was difficult. 
The solution: Notes: 
Establish an arc between water-cooled tungsten- 1. The experimental arc facility of this investigation 
tipped electrodes, maintain the arc along the center- is considered to be a useful tool for the study of 
line of a central jet of argon gas, and surround the radiant heat transfer processes at high temperatures. 
argon jet with a coaxial sheath of nitrogen. 2. The following documentation
	 may be obtained 
How it's done: from: 
Water-cooled	 copper	 electrodes	 were	 equipped Clearinghouse for Federal Scientific 
with	 tungsten	 tips.	 In	 operation,	 the	 tips	 are	 at and Technical Information 
sufficiently high temperatures to melt the ends and Springfield, Virginia 22151 
ensure adequate thermal electron emission for reig- Single document price $3.00 
nition as the arc current passes through zero. This (or microfiche $0.65) 
contributes significantly to arc stability. Argon was 
chosen as the central jet gas because it is relatively Reference: NASA TM-X-52424(N68-
easy to ionize and produces a highly radiant plasma. 21242), Coaxial-Flow Stabilization of an 
An outer sheath of nitrogen surrounds the argon jet Alternating-Current Plasma Arc 
to provide further stabilization. 3. Technical questions may be directed to 
A low-frequency ac arc of this design was built Technology Utilization Officer 
and operated at arc frequencies from 12 to 22 Hz. Lewis Research Center 
The outer gas sheath velocity was varied from zero 21000 Brookpark Road 
up to a value greater than that of the inner gas jet. Cleveland, Ohio 44135 
Arc	 behavior was quite	 insensitive	 to	 changes	 in Reference: B70-10065 
velocity of either the inner or outer gas streams. The Patent status: 
arc column diameter did not change with increasing No patent action is contemplated by NASA. 
flow rate of either of the two coflowing gases. (A Source: Chester D. Lanzo 
"thermal pinch" effect normally occurs as the external Lewis Research Center 
cooling of the gas jets decreases the column diameter (LEW-10442)
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Aeronautics and Space Administration. Neither the United States
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A stabilized low-frequency alternating-current electric arc

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