Vortex stabilized plasma arc used to obtain spectral energy distribution dat

Mc Intosh, R.

Neuder, S.

Urschel, R.

English

NASA Technical Reports Server

1 
~ X- 71 3-67-81 
RECENT PROGRESS WITH THE 
VORTEX STABILIZED ARC 
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BY \ 
STAN NEUDER 
ROBERTA URSCHEL 
ROY MclNTOSH 
FEBRUARY 1967 
\ 
GODDARD SPACE FLIGHT CENTER - 
GREENBELT, MARYLAND I ;  
, 
https://ntrs.nasa.gov/search.jsp?R=19670012071 2020-03-24T01:07:58+00:00Z
X-713-67-81 
7 
- RECENT PROGRESS WITH THE 
? 
VORTEX STABILIZED A R C  
' Stan Neuder 
Roberta Urschel* 
Roy McIntosh* 7 
1 February 1967 . 
2 
"Electromechanical Research, Contract NAS 5-9244 
i GODDARD SPACE FLIGHT CENTER 
Greenbelt, Maryland . 
RECENT PROGRESS WITH THE 
VORTEX STABILIZED ARC 
Stan Neuder 
Roberta Urschel 
Roy McIntosh 
ABSTRACT 
Spectroradiometric investigations of vortex stabilized, inert gas 
plasmas continue in order  to achieve an improved spectral match. 
Results of recent measurements on argon, neon, and argon-neon plas- 
mas  are presented. A significant step towards the desired spectrum 
is achieved with certain argon-neon combinations. A description of 
the vortex a r c  and associated experimental apparatus is included. 
iii 
RECENT PROGRESS WITH THE 
VORTEX STABILIZED ARC 
1. Vortex A r c  Description 
Figure 1 is a sketch of the vortex stabilized source. The tungstenelectrodes 
are axially positioned within two concentric quartz cylinders. The gas enters 
under pressure behind the anode section, passes  between the cylinders and into 
the cathode. It is spirally injected into the inner chamber through nearly- 
tangential orifaces in the cathode wall and is exhausted through the central bore 
of the anode. The vortex restricts the plasma to well-defined cylindrical sym- 
metry with typical dimensions of 2 mm diameter and 10 mm length. The exhaust 
gas is cooled in the heat exchanger and is continuously recirculated by means of 
compressors. Gas pressure may be increased to over 20 atm. There is no gas 
loss during operations and almost all is retrievable when desired. 
The power input may be varied from about 3,000 to 25,000 watts with cur- 
rents up to 250 amps readily obtainable. The electrodes and small cylindrical 
housing (not shown) are water cooled. 
2. Instrumentation 
Figure 2 is a block diagram of the experimental apparatus used for obtain- 
ing the spectral radiation data. The Leiss double prism monochromator is 
calibrated in the spectral range 0.25 to 2.4 microns. 
The radiation is chopped at the entrance slit of the integrating sphere and 
detected by a photomultiplier o r  photoconductive cell. The signal is displayed 
on a strip chart recorder. The measured response is  calibrated with a 1000 
watt quartz iodine standard of spectral irradiance. 
Figure 3 is a simplified sketch of the optical system. The calibrated filter 
is used only in the a r c  beam. 
3. Plasma and Electrode Life 
A typical stabilized argon plasma is shown in Figure 4. This is a 40 amp, 
1.5 mm diameter column at 4 KW input and 8 atm. The diameter increases to 
2.5 mm for a 200 amp plasma. 
1 
Electrode lifetime is quite high in argon. Figure 5 shows the cathode and 
anode following more than 100 hours of intermittent operation in argon at vari- 
ous current levels. The gas orifaces are clearly discernible in both. 
Electrode lifetime is short in neon and helium plasmas. Electrodes follow- 
ing only a few hours in neon is shown in Figure 6 most of the tungsten loss from 
the cathode is deposited on the anode and inner quartz envelope. 
4. Spectral Measurements 
A. Argon-The relative spectral distributions of argon at 5 KW and 20 KW 
and 8 atm are  shown in Figures 7 and 8. The spectra are combinations of con- 
tinuum and line broadened emission. Comparison shows that the effect of in- 
creased current is manifested in increased ultraviolet content and an increased 
ratio of continuum to line emission. 
For greater ease of comparison emission spectra has been replotted in 
t e rms  of energy per  unit bandwidth, as shown in Figure 9. The curves are that 
of argon at 16 atm, 5 KW and 16 atm, 20 KW. The energy redistribution is now 
evident. 
'The effect of increased pressure on a 20 KW argon plasma is shown in Fig- 
ure  10. The pressure change from 8 atm to 16 atm results in a redistribution 
of emitted energy in the 2500A-5500A wavelength region. This redistribution 
was not found in a 5 KW argon plasma. 
B: Neon-Spectral measurements on neon were made at 4 KW and 16 KW, 
and 10 atm. The emission is a combination of line and continuum. Most of the 
energy is radiated in the 5500A-7500A region as seen in Figure 11. A consid- 
erable change in spectral distribution was found primarily in the 3500A-5500A 
region for the two power settings. 
C. Argon-Neon Mixtures-Figure 12 is the spectral  energy distribution of 
argon at 5 KW and of neon at 16 KW, superposed on the solar distribution at air 
mass zero. 
With respect to the Johnson curve, it is seen that the argon spectrum alone 
is deficient throughout the visible wavelength range but has an  excessive of UV 
continuum and near IR line emission. The neon spectrum alone is deficient at 
all wavelengths below 5500A and above 8000A but has excessive emission be- 
tween 5500A-7500A. 
2 
Several mixtures of neon-argon were tried. The results of a 50% Argon- 
50% Neon combination at 4 KW and 7 atm is shown in Figure 13. The 100% 
argon curve is included for comparison. 
The spectral emission of the two gas plasma is basically that of pure argon. 
A s  expected from theoretical considerations, this was  found for other neon-argon 
combinations having argon as the major constituent. In order to balance the 
excitation probabilities, a 90 Ne-10 Ar combination at 4 KW and 4 atm was tried. 
This is shown in Figure 14. Again, direct comparison may be made with the 
included curve of pure argon at 5 KW and 4 atm. 
The near IR transition of the first electronic excitation levels of both com- 
ponents appear equally likely in the 90-10 distribution at the 4 KW setting. 
Transitions from the second excitation levels of argon are still present but 
considerably weakened. 
The most favorable result of this series was obtained with a 80% Ne-20% Ar 
plasma. Figure 15 compares an 80 Ne-20 Ar ,  4 KW plasma with 100% A r  5 KW 
plasma. Both are superposed on the solar distribution. 
CONCLUSIONS 
Adjustments have been made in the spectral energy distribution and con- 
tinuum to line emission ratio by varying the plasma current and ambient pres- 
sure. Adjustments in the spectral emission intensities, at fixed plasma currents 
have been accomplished statistically. 
Although a proper neon-argon combination presents an improved spectral 
match above that of the individual components alone, it is still deficient, (at 
least at the lower power and pressure levels), in the 4000A-6000A region. 
Based on theoretical considerations and experimental results obtained, it is 
felt that further improvements in the spectral match will be achieved by (a) in- 
creased power input at different pressure ambients and (b) the presence of 
other gaseous components in the plasma. 
These two approaches will be pursued. 
3 
\ 
M A T  EXCHAUnBER 
BAS IN 
*no# WATER 
OUT 
LCATHOOE 
CAT- WATER OUT 
f- ANODE 
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WATER IN 
* 12* ___.) 
Figure 1. Vortex arc 
.... 
CATHOOE 
LCONCENTRIC 
TUBES 
MONOCHRO - 
DETECTOR 
CHOPPER 
I k I L E k l  
RESISTOR 
STANDARD SUPPLY 
PRf AMPLIFIER i v  
RECORDER l 
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Figure 2. Instrumentation 
4 
I 
Figure 3. Optical system 
Figure 4. Argon plasma 4 KW, 8 atm, 40 amps 
5 
Figure 5. Electrodes after 100 hrs. in Argon 
Figure 6. Electrodes after a few hrs. in Neon 
6 
v - 2  
RELATIVE SPECTRAL DISTRIBUTION 
VORTEX STABILIZED ARC WITH 
ARGON AT 8 ATM, 5 KW, STANDARD 
ELECTRODES 
FEE. 18,1966 
STANDARD LAMP Q M - S I  
WAVELENGTH (nanometers) 
Figure 7. Argon spectral distribution at 5 KW 
v - 7  
RELATIVE SPECTRAL DISTRIBUTION 
VORTEX STABILIZED ARC WITH 
A R G O N  AT 8 ATM, 20 KW, STANDARD 
ELECTRODES 
MAR. 18,1966 
STANDARD LAMP QM-SI 
WAVELENGTH (nanometers) 
Figure 8. Argon spectral distribution at  20 KW 
7 
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WAVELENGTH (nanometwsl 
Figure 15. 80% Ne-20% Ar at 4 KW, 100% Ar at  5 KW 
and the solar distribution 
2000 
11 


Recent progress with the vortex stabilized arc

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