Enhancement of energy confinement by acceleration of fast ions in combined lower hybrid and neutral beam heating on JT-60

Abstract
A strong ion tail with a temperature of ~ 60 keV was produced in JT-60 by lower hybrid wave acceleration of neutral beam injected fast ions. The incremental energy confinement time due to neutral beam heating of a lower hybrid heated plasma was improved by more than a factor of two and reached approximately 110 ms. The confinement of the tail ions is classical and the improvement of confinement can be fully explained by the contribution of the fast ions. The heating process of the beam ions is consistent with the predictions of the quasi-linear theory.