Parametric upconversion of lower hybrid wave by runaway electrons in tokamak

TL;DR

This paper develops a kinetic formalism to analyze how large amplitude lower hybrid waves can parametrize and upconvert via runaway electrons in tokamaks, potentially generating relativistic electrons.

Contribution

It introduces a new kinetic model describing parametric decay involving runaway electrons and demonstrates the process's potential to produce relativistic electrons in tokamaks.

Findings

Growth rate scales as the square of the pump amplitude

Finite velocity spread turns instability into stimulated Compton scattering

Generated waves can produce relativistic electrons

Abstract

A kinetic formalism of parametric decay of a large amplitude lower hybrid pump wave into runaway electron mode and a uppersideband mode is investigated. The pump and the sideband exert a ponderomotive force on runaway electrons, driving the runaway mode. The density perturbation associated with the latter beats with the oscillatory velocity due to the pump to produce the sideband. The finite parallel velocity spread of the runaway electrons turns the parametric instability into a stimulated compton scattering process where growth rate scales as the square of the pump amplitude. The large phase velocity waves thus generated can potentially generate relativistic electrons.