A scheme for evaluating Te/Ti and Z¯ by light scattering

When highly ionized impurities are present in a plasma, the scattered spectrum of the major ion species can be distorted in a complicated way. A method is given by which T_e/T_i and Z¯ (≡Jn_jz_j²/n_e) can be measured which does not require any knowledge of the mass, charge state, or concentration of the impurity species. A generalization of the Salpeter approximation for the integrated cross section is proven. The result is that the total cross section is a function of α (≡ 1/Kλ_D), T_e/T_i, and Z¯ as long as the temperature of all ion species is the same and T_e/T_i is not too large. Thus a measurement of the integrated ion cross section at two different scattering angles can yield T_e/T_i and Z¯. This method is insensitive to magnetic fields and to moderate electron drifts. For 1≲T_e/T_i, Z¯≲3 the cross section must be measured to an accuracy of about 3% to give T_e/T_i to within 10% and Z¯ within 20%.