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Electrical Measurements on a Moving Argon Plasma

Conference:

Abstract

Experimental current-voltage characteristic curves were obtained for a moving argon plasma at two stations in an electrically-driven 5 cm shock tube. The standard energy was 1 kj and the base pressure 10 torr, giving a shock of about Mach 4. The measurements were made on the highly-ionized driver gas which followed the shock at speeds between 800 and 1100 m/sec. Two types of electrode were used. One comprised circular solid electrodes of aluminium, molybdenum or stainless steel so machined as to be quite flush with the tube wall; the other comprised filaments of tungsten wire which were immersed in the free stream and could be used cold or heated for thermionic emission. Characteristics were obtained both for applied voltages and for MHD-generated voltages; for the latter a magnetic field of good uniformity up to 0.9 Wb/m{sup 2} was used. The results were always markedly dependent on the surface condition of the electrodes. For consistent results the flush electrodes had to be cleaned carefully by hand after every third discharge, while the filament electrodes were thermionically cleaned before every discharge. In general the cold electrode characteristics for applied voltage showed three distinct regions: a current increase such as would be expected  More>>
Authors:
Abbas, A. A.M.; Howatson, A. M. [1] 
  1. Oxford University (United Kingdom)
Publication Date:
Oct 15, 1966
Product Type:
Conference
Report Number:
IAEA-SM-74/26
Resource Relation:
Conference: Symposium on Magnetohydrodynamic Electrical Power Generation, Salzburg (Austria), 4-8 Jul 1966; Other Information: 15 refs., 8 figs.; Related Information: In: Electricity from MHD. Vol. I. Proceedings of a Symposium on Magnetohydrodynamic Electrical Power Generation| 728 p.
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ALUMINIUM; ARGON; BOUNDARY LAYERS; COMPARATIVE EVALUATIONS; CURRENT DENSITY; ELECTRIC POTENTIAL; ELECTRODES; ELECTRON MOBILITY; EXTRAPOLATION; IONS; MAGNETIC FIELDS; MAGNETIC PROBES; MAGNETOHYDRODYNAMICS; MOLYBDENUM; PLASMA; SATURATION; STAINLESS STEELS; THERMIONIC EMISSION; TUNGSTEN
OSTI ID:
22113805
Research Organizations:
International Atomic Energy Agency, Vienna (Austria); European Nuclear Energy Agency of the OECD, Issy-les-Moulineaux (France)
Country of Origin:
IAEA
Language:
English
Other Identifying Numbers:
Other: ISSN 0074-1884; TRN: XA13M1691070787
Submitting Site:
INIS
Size:
page(s) 175-189
Announcement Date:
Jul 20, 2013

Conference:

Citation Formats

Abbas, A. A.M., and Howatson, A. M. Electrical Measurements on a Moving Argon Plasma. IAEA: N. p., 1966. Web.
Abbas, A. A.M., & Howatson, A. M. Electrical Measurements on a Moving Argon Plasma. IAEA.
Abbas, A. A.M., and Howatson, A. M. 1966. "Electrical Measurements on a Moving Argon Plasma." IAEA.
@misc{etde_22113805,
title = {Electrical Measurements on a Moving Argon Plasma}
author = {Abbas, A. A.M., and Howatson, A. M.}
abstractNote = {Experimental current-voltage characteristic curves were obtained for a moving argon plasma at two stations in an electrically-driven 5 cm shock tube. The standard energy was 1 kj and the base pressure 10 torr, giving a shock of about Mach 4. The measurements were made on the highly-ionized driver gas which followed the shock at speeds between 800 and 1100 m/sec. Two types of electrode were used. One comprised circular solid electrodes of aluminium, molybdenum or stainless steel so machined as to be quite flush with the tube wall; the other comprised filaments of tungsten wire which were immersed in the free stream and could be used cold or heated for thermionic emission. Characteristics were obtained both for applied voltages and for MHD-generated voltages; for the latter a magnetic field of good uniformity up to 0.9 Wb/m{sup 2} was used. The results were always markedly dependent on the surface condition of the electrodes. For consistent results the flush electrodes had to be cleaned carefully by hand after every third discharge, while the filament electrodes were thermionically cleaned before every discharge. In general the cold electrode characteristics for applied voltage showed three distinct regions: a current increase such as would be expected from a double probe; a saturation region; and a linear increase, in order of increasing voltage. For the flush electrodes another apparent saturation was found before, finally, the transition to an arc-type discharge. The first saturation current for flush electrodes corresponded to a random ion current much less than that estimated to exist away from the tube walls, as is expected from a consideration of diffusion through a boundary layer. The value of the current varied somewhat with the electrode material. For the cold filaments, the saturation current density was of the same order as for the flush electrodes. From the linear region of the curves, an effective plasma conductivity was obtained. For comparison, the plasma conductivity at various radii was measured by a Lin-type magnetic probe within the tube; this gave the actual conductivity, i.e. virtually that due to electron mobility. The ionic component, calculated from this, agreed well with the effective conductivity from the curves, as expected when conduction is inhibited by the continuity requirement of non-emitting electrodes. Similar regions could be distinguished for the MHD characteristics. By extrapolation, the sheath voltage drop was found to be between 1.2 and 4 V, depending on conditions, for flush electrodes, and only a fraction of a volt for the cold filaments. , The characteristics for emitting electrodes also showed three regions: an initial, nearly linear rise, followed by a saturation current, equal to the thermionic current added to the cold saturation value, and then a rapid rise indicating either a very high conductivity or a tendency to constant current density. The most obvious explanation of the last region is that the plasma shows its normal conductivity, i.e. virtually electronic, but the maximum currents drawn greatly exceeded the available emission. From the plasma conductance at different magnetic fields estimates of charged particle mobilities have been made. (author)}
place = {IAEA}
year = {1966}
month = {Oct}
}