Kinetic theory of effect of dust charge fluctuations on the parametric decay of lower hybrid wave instability by relativistic runaway electrons in tokamak

Abstract

Dust charge fluctuation effect on the parametric decay of lower hybrid wave instability by relativistic runaway electrons is studied in a tokamak using kinetic treatment. Parametric upconversion of lower hybrid pump waves into relativistic runaway electron mode and upper sideband mode is described. A ponderomotive force is exerted on the runaway electrons by lower hybrid pump wave possessing large amplitude and upper sideband wave, which drives the runaway electron mode. The coupling of the oscillatory velocity of electrons with density perturbations produces nonlinear density perturbations on the upper sideband frequency. As a result, runaway generation is enhanced by a lower hybrid wave and the growth rate of the instability is measured as the square of the amplitude of the pump wave. Moreover, the presence of dust charge fluctuations and their number density in the tokamak have an appreciable effect on the growth rate of lower hybrid wave instabilities, which in turn affects the actual performance of the ITER due to the potential safety and operational issues.