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Title: Mach probe interpretation in the presence of suprathermal electrons

Abstract

The collisionless theory of Mach probes assuming isothermal, Maxwellian electrons is extended to include an isotropic, two-temperature electron distribution function. The kinetic equations for ion and electron motion in the probe wake are solved using a quasineutral particle-in-cell method, which compares qualitatively well with the results of a simple fluid model. The measured Mach number decreases slightly with increasing hot electron concentration, but the main effect is on the measured electron temperature. Due to the fact that the probe is sensitive to even a tiny population of hot electrons, the resulting ion sound speed can be overestimated by up to a factor of 2, leading to measurements of absolute flow speed that are too large.

Authors:
;  [1];  [2]
  1. Centre de Cadarache, Association EURATOM-CEA, CEA/DSM/DRFC, 13108 Saint Paul Lez Durance (France)
  2. (Czech Republic)
Publication Date:
OSTI Identifier:
20974881
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 3; Other Information: DOI: 10.1063/1.2672896; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AUGMENTATION; DISTRIBUTION FUNCTIONS; ELECTRON TEMPERATURE; ELECTRONS; ION TEMPERATURE; IONS; KINETIC EQUATIONS; MACH NUMBER; PLASMA; PLASMA SIMULATION; PROBES; SOUND WAVES

Citation Formats

Gunn, J. P., Fuchs, V., and Association EURATOM/IPP.CR, Za Slovankou 3, 18200 Prague 8. Mach probe interpretation in the presence of suprathermal electrons. United States: N. p., 2007. Web. doi:10.1063/1.2672896.
Gunn, J. P., Fuchs, V., & Association EURATOM/IPP.CR, Za Slovankou 3, 18200 Prague 8. Mach probe interpretation in the presence of suprathermal electrons. United States. doi:10.1063/1.2672896.
Gunn, J. P., Fuchs, V., and Association EURATOM/IPP.CR, Za Slovankou 3, 18200 Prague 8. Thu . "Mach probe interpretation in the presence of suprathermal electrons". United States. doi:10.1063/1.2672896.
@article{osti_20974881,
title = {Mach probe interpretation in the presence of suprathermal electrons},
author = {Gunn, J. P. and Fuchs, V. and Association EURATOM/IPP.CR, Za Slovankou 3, 18200 Prague 8},
abstractNote = {The collisionless theory of Mach probes assuming isothermal, Maxwellian electrons is extended to include an isotropic, two-temperature electron distribution function. The kinetic equations for ion and electron motion in the probe wake are solved using a quasineutral particle-in-cell method, which compares qualitatively well with the results of a simple fluid model. The measured Mach number decreases slightly with increasing hot electron concentration, but the main effect is on the measured electron temperature. Due to the fact that the probe is sensitive to even a tiny population of hot electrons, the resulting ion sound speed can be overestimated by up to a factor of 2, leading to measurements of absolute flow speed that are too large.},
doi = {10.1063/1.2672896},
journal = {Physics of Plasmas},
number = 3,
volume = 14,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • Several investigators have computed ionospheric electron heating rates in the past using an incorrect term in the expression for the energy transfer from the suprathermal to the thermal electrons derived by Mantas (1975). This incorrect formulation was also based on an electron energy loss rate inversely proportional to the suprathermal electron energy, limiting its application to energies above about 2-3 eV. Since the proper low-energy cutoff is the cross-over energy at which the thermal electron intensity equals the suprathermal one, a considerable portion of the ambient electron heating may take place below 2-3 eV, depending on the ionospheric conditions. Mantasmore » (1981) has amended these inadequacies, but has not explored their geophysical consequences. Comparing electron heating rates and electron temperatures computed by the incorrect approach with identical computations based on the proper energy transfer term, energy loss rate and cross-over energy, we find that the previous approach lends to a substantial underestimate of the ambient electron heating rate as well as the resulting ionospheric electron temperature. This underestimate is more pronounced for solar minimum than for solar maximum conditions as could be anticipated since the elevated electron densities and temperatures at solar maximum lead to a higher cross-over energy and thus a lesser impact of the inadequacies in previous treatments.« less
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  • The nonlinear dynamics of electron-acoustic localized structures in a collisionless and unmagnetized plasma consisting of ''cool'' inertial electrons, ''hot'' electrons having a kappa distribution, and stationary ions is studied. The inertialess hot electron distribution thus has a long-tailed suprathermal (non-Maxwellian) form. A dispersion relation is derived for linear electron-acoustic waves. They show a strong dependence of the charge screening mechanism on excess suprathermality (through {kappa}). A nonlinear pseudopotential technique is employed to investigate the occurrence of stationary-profile solitary waves, focusing on how their characteristics depend on the spectral index {kappa}, and the hot-to-cool electron temperature and density ratios. Only negativemore » polarity solitary waves are found to exist, in a parameter region which becomes narrower as deviation from the Maxwellian (suprathermality) increases, while the soliton amplitude at fixed soliton speed increases. However, for a constant value of the true Mach number, the amplitude decreases for decreasing {kappa}.« less