BEAM-DRIVEN CURRENTS IN THE 1/NU REGIME IN A HELICAL SYSTEM

Beam currents driven by a neutral particle injection in a helical system (stellarator, heliotron/torsatron) are studied in the 1/v collisionality regime. The general expres-sion for the beam-driven current is obtained for arbitrary magentic field configurations by solving the drift kinetic equation for electrons. It is found that F=Jnet/Jb (Jnet is the net current and Jb is the fast ion beam current) increases as ft and Zeff where ft is the fraction of trapped electrons and Zeff is the effective ionic charge number. Especially, for Zeff ≃ 1 the effect of trapped electrons is large and F is roughly proportional to ft. On the other hand, if Zeff ≳ 3 the effect of trapped electrons becomes small. © 1990, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.