Simultaneous heating by high power lower hybrid waves and neutral beams in the JT-60 tokamak

Abstract

By injection of high power lower hybrid (LH) waves of up to 6.0 MW into neutral beam heated (20 MW) plasmas in the medium electron density regime (e ≤ 3.5 × 1019 m-3) the plasma energy content is increased at the same incremental energy confinement time as it is increased with neutral beam heating alone. When LH heating is used in addition to thermal electron and ion heating, the beam ions are accelerated to energies considerably higher than the beam injection energy. In contrast to LH injection into ohmically heated plasmas in the same density regime, where substantial high energy electron production is observed, there are much less high energy electrons in the case of combined heating. The heating efficiency of LH waves during combined heating tends to decrease as the electron density is increased. Ray tracing analysis suggests that the accessibility condition prevents effective heating in a high density plasma. Calculation of wave damping, taking into account the beam component of the ion velocity distribution function, indicates that the waves are absorbed by beam ions before they are absorbed by electrons.