Spectroscopic observation of a helium plasma cooled by a hydrogen gas injection

Study of recombining plasmas resulting from a neutral gas injection has bee n made in a high density steady-state plasma. Recently, the inverted popula tion between He I 1s2p(1) P and 1s3p(1) P due to the selective double elect ron capture process, He2+ + H-2 --> He+ (1s3l) + 2H(+), was observed in a s ingle layer column plasma [S. Namba et al., Fusion Eng. Design 34-35 (1996) 777], when a helium plasma contacts with a hydrogen molecule. Moreover, ex perimental results which suggest an effect of the vibrational states of hyd rogen molecules, He2+ + H-2 (v') --> He* (1s nl; n = 3, 4, 5) + 2H(+), have been obtained for a double layer column plasma which was generated by a ch ange of helium gas flow rate into the discharge region. The results on the hydrogen gas injection experiments relevant to two plasma conditions are pr esented. (C) 1999 Elsevier Science B.V. All rights reserved.