Resonance radiation and high excitation of neutrals in plasma-gas interactions

Experimental investigation of plasma-gas interaction has been performed in LENTA linear facility in order to model processes expected to occur in the divertor of a fusion tokamak reactor. Steady-state helium plasma with densi ty similar to (0.2-3) x 10(13) cm(-3) generated by beam-plasma discharge fl owed into the region with high neutral pressure, interacted with neutral he lium there and then reached the target plate. An intensive Volume recombina tion and significant decrease in plasma pressure have been observed while t he plasma stream interacted with gas target. Electron temperature fell belo w 1 eV. These processes were accompanied by an intensive emission from high ly excited helium atoms and this radiation became even higher with increase in neutral pressure. Microwave emission absorption at high (P-gas = 20 mTo rr) neutral pressures in the gas target was detected. A model of plasma-gas transition layer was developed to provide physics understanding of these p henomena. Resonance radiation and stimulated radiative recombination play a n important role in this model. (C) 2001 Elsevier Science B.V. All rights r eserved.