Optically Thin Hydrogen Plasma with Self-Consistent Electron Velocity Distribution

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Abstract
Occupation numbers of the atomic levels and degree of ionization of a stationary optically thin hydrogen plasma are calculated for temperatures in the range 8000 °K ≲ T ≲ 16000 °K and for electron densities in the range 109 cm-3 ≲ ne ≲ 1017 cm-3. The electron velocity distribution is not supposed to be Maxwellian, rather, it is obtained in a self-consistent way from the corresponding kinetic equation which is solved simultaneously with the equations that describe the statistical steady-state of the atomic levels. Besides spontaneous radiative bound-bound transitions and radiative recombinations, inelastic electron-atom collisions as well as elastic electronelectron and electron-atom collisions are taken into account. Hydrogen atoms are approximated by model atoms having four bound levels and a continuum. The numerical results show that for temperatures T ≲ 10000 °K the tail of the electron distribution function differs markedly from that of a Maxwell distribution, except in the case of high electron densities. Likewise, the selfconsistently calculated values of the atomic occupation numbers and of the degree of ionization there deviate strongly, up to several orders of magnitude, from those obtained by assuming a Maxwellian velocity distribution of the electrons.

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