An Extension of the Theory for Neutral-Beam-Driven Currents in Tokamaks

Abstract

A self-consistent theory is presented for the calculation of neutral beam driven currents in tokamaks, including for the first time the effects of radial transfer of toroidal momentum, background ion rotation, and fast beam ion pressure gradients. The new theory contains the beam current, electron return current with trapping effects, and the bootstrap current contributions of previous theories, but extended to be consistent with particle and momentum balance and ambipolarity in a rotating plasma with the radial transfer of toroidal momentum and a significant fast beam ion population. It is found that these new effects can be significant. TFTR model problem calculations indicate that the beam driven current can be reduced by as much as 30% and the bootstrap current can be increased by as much as 100%, relative to predictions based on the standard theory.