
Author(s):
S. Sasaki, M. Goto, T. Kato and S. Takamura

Title:
Line Intensity Ratios of Helium Atom in an Ionizing Plasma
Date of publication:
Oct. 1998

Key words:
helium atom, plasma diagnostics, Iine intensity ratio, collisional radiative model, hot electrons, resonance scattering

Abstract:
Effective emission rate coefficients C_em^eff(lambda), line intensity rations, C_em^eff(lambd_1)/C_em^eff(lambd_2), and S^eff/ C_em^eff(lambda), with S^eff the ionization rate coefficient, are obtained by the collisional radiative model for an ionizing plasma using new excitation and ionization rate coefficients. In the plasma with electron density n_e > 10^4 cm^3, C_em^eff(lambda) for various lines are enlarged, since the normalized population densities for the metastable states, n(2^{1,3}S)/n_{He}, becomes large, and the excitation rate coefficients from 2^{1,3}S, C_ {2^{1,3}s rightarrow i}, are large compared to that from the ground state C_{1^{1}s rightarrow i}. In high , n_e Plasma (n_e > 10^12 cm^3), with frequent electron impacts on the excited heliums, n(i)/n_He become constant to n_e, which results in the decrease of C_em^eff(lambda). Hot electrons and resonance scattering, which are often important for the experimental applications, are included in this model. A small amount of hot electrons (several percents) can enhance the line emission and ionization rates for low electron temperature plasma with T_e (T_e< 10 eV). The resonance scattering reduces the emission of the resonance lines (1^1S  n^l P) and enlarges n^1 P and 2^1S populations when the column density of helium gas n_He x L exceeds 2 x 10^13[cm^2].

