Study of ion line broadening in the Tormac discharge

Abstract

Tormac (Toroidal Magnetic Cusp) is a Magnetic confineaent plasaa concept having absolute minimum-B geoaetry. Two versions of Toraac are considered here. Tornac T IV-c has a glass vessel of rectangular cross section, 0.5 m in diameter. The confineaent field rises to-4.5 fcG in-8.3 usee. Tonnac T V has a T-shaped glass vessel, 1 n in diameter, with a field of-3 kG, rising in-10 ysec. Gaussian Hell 4686 A spectral liner having full widths at half maximum over 2 A have been observed in both Tomac plasaas. Interpre tation of these widths as due to thermal Ooppier broadening would give ion temperatures of > 100 eV, in contradiction with other diagnostics. Indications are that these widths are not siaply explained either by thermal Doppler broadening, or Stark broadening due to interparticle fields. Magnetic probe measurements indicate that compressions' Alfver mode* are excited by the main containment field rise in T IV-c. No indication of this was found in T V. The fluid notion associated with this mode is used to explain the broadening of Kell 4686 A durirq cusp field rise in T IV-c, at which time the broadening is greatest. After field peak, the broadening is explained as Stark broadening due to turbulence excited by a large toroidal plasaa current, which persists long after cusp peak. This current is larger in T V, and is taken as the sole mechanism for the line broadening.