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Brown 1982
Brown, R.A. (1982). The probability distribution of S+ gyrospeeds in the Io Torus. Journal of Geophysical Research 87. doi: 10.1029/JA087iA01p00230. issn: 0148-0227.

We report a measured probability distribution of S+ gyrospeeds in the Io torus derived from [S II> 6716 ¿, 6731 ¿ emission line profiles recorded at axial distance 5.9 RJ from Jupiter. This ion species is not in kinetic thermodynamic equilibrium. An artifical spectral decomposition in terms of three Maxwellian distributions finds perpendicular temperatures T = 2.7,28, and 192 eV with weights 0.28, 0.50, and 0.22, respectively. The average temperature is about 60 eV, which would be seriously underestimated by a simple measurement of the line width. We find upper limits of ~5% or ~20%, to the mixing ratios of S+ ions having the pickup speed of ionized ballistic atoms, assuming a flat or isotropic patch angle distribution, respectively. Due to the low S+ density and charge, Coulomb collisional power transfer from the observed S+ population to the ambient electrons delivers only 0.01 eV cm-3 s-1, or 1/40 the UV emission power requirement. Existing [S III> linewidth temperatures indicate S2+ is hotter than S+, indicating that kinetic thermodynamic equilibrium exists neither between nor within species in the hot, outer plasma torus.

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Journal of Geophysical Research
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