Light, Plasma, and Microscopic Processes

Abstract

Glow discharges with different gases in the Large Helical Device (LHD at the National Institute for Fusion Science (NIFS show different visual colors of the plasma and these colors are ascribed to different spectra in the UV and visible wavelength range. From the wavelengths of the observed emission lines these gases are identified as neon helium and hydrogen. The emission line intensity is given by the upper level popula‑ tion density of the corresponding transition via the spontaneous transition probability or Einstein's A coeffi‑ cient. On the assumption of corona equilibrium relative emission line intensities of neutral helium are esti‑ mated for thetotransitions. The results are in gross disagreement with the glow discharge spec‑ trum. For a single pulsed helium discharge in a Pyrex tube line emissions are intense during the beginning of the pulse and after the pulse [A. Hirabayashi et al., Phys. Rev. A 37 77 (1988]. The population distribution over the levels is determined for these two emission peaks and neither of the results agrees with the expectationsfromcoronaequilibrium.Itisalsofoundthatthecoloroftheplasmaobservedforamaindischarge withhelium inLHDisdrasticallydifferent dependingontheplasmaconditionandnevershowsasimilarcolor tothatintheglowdischarge.Alltheseresultsindicatebreakdownofcoronaequilibriumanddemandusdeeper considerations.