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The ADAS208 collisional-radiative model was employed to calculate excitation, ionization and recombination coefficients for hydrogen atoms and optically thin, as well as optically thick plasma conditions. The excitation and recombination coefficients were analysed to separate the 2 contributions to spectral line emission for ionization degrees far from equilibrium. If the ground state excitation is significant, the plasma neutral density can be measured from the Balmer spectral line emission. However, the electron temperature must be known precisely for this procedure, and most likely the neutral density cannot be determined in this way in the ASDEX Upgrade divertor and for the density limit conditions, because it is too low. These plasmas are probably characterized by volume recombination, but recombination only plays a role as a particle sink if the flow velocities are substantially below sound speed.

Additional information

Authors: BEHRINGER K, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP 10/5 EN (1997) 21pp.
Availability: Available from the Max-Planck-Institut für Plasmaphysik, 85748 Garching bei München (DE)
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