Low Threshold Parametric Decay Back Scattering Instability in Tokamak ECRH Experiments

TL;DR

This paper analyzes how plasma density variations and magnetic field inhomogeneities in tokamaks lower the threshold for parametric decay backscattering instability during ECRH experiments, enabling wave localization and instability onset.

Contribution

It introduces a detailed analysis of plasma conditions that significantly reduce the decay instability threshold in tokamaks, including calculations of wave gain and pump power thresholds.

Findings

Plasma density non-monotonicity near magnetic islands reduces decay instability threshold.

Magnetic field inhomogeneity enables ion Bernstein wave localization.

Calculated ion Bernstein wave gain and pump power thresholds for instability.

Abstract

The experimental conditions leading to substantial reduction of backscattering decay instability threshold in ECRH experiments in toroidal devices are analyzed. It is shown that drastic decrease of threshold is provided by non monotonic behavior of plasma density in the vicinity of magnetic island and poloidal magnetic field inhomogeneity making possible localization of ion Bernstein decay waves. The corresponding ion Bernstein wave gain and the parametric decay instability pump power threshold is calculated.