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Collisional-radiative recombination and ionization coefficients, α andS, have been calculated on the basis of a non-hydrogen-like collisional-radiative model for atomic helium. The singlet and triplet systems have been considered as two individual systems coupled to each other through a set of elementary processes for collisions and radiation. Auto-ionization states have not been taken into account. Therefore the computations of the coefficient α have been limited to the range 125≦Te[°K]≦64000. (AboveTe=64 000 °K the auto-ionizing states considerably influence the recombination rates (di-electronic recombination).) The results show that the α- andS-coefficients for helium are more sensitive to radiative trapping than those for hydrogen under comparable absorption conditions. Concerning the α-values: For low electron densities one obtains approximately αhelium≈2αhydrogen, whereas at high electron densities one finds approximately αhelium≈1/2αhydrogen (to 1/10 αhydrogen at high electron temperatures). Collisional-radiative ionization coefficients for atomic helium have not yet been published in the past. In the present paper one finds for the first time a complete set ofS-coefficients for different degrees of radiative trapping. |
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