Beam-Driven Currents in the 1/ν 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/ν collisionality regime. The general expression 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 = J net / J b ( J net is the net current and J b is the fast ion beam current) increases as f t and Z eff where f t is the fraction of trapped electrons and Z eff is the effective ionic charge number. Especially, for Z eff ≃1 the effect of trapped electrons is large and F is roughly proportional to f t . On the other hand, if \(Zeff3\) the effect of trapped electrons becomes small.