On the possibility of low-threshold decay of an obliquely propagating ordinary wave into electron and ion Bernstein waves in ITER ECRH experiments

The low-threshold parametric decay of an obliquely propagating ordinary wave into electron and ion Bernstein waves in a plasma with a monotonic density profile is considered. This particular scenario is critical as it provides a mechanism for direct nonlinear energy transfer from the pump beam to both the electron and ion components of the plasma, even under conditions when the ECR absorption is expected by the linear theory to be localized elsewhere. Given its practical significance for future electron cyclotron resonance heating operations on ITER, the results of the analysis are illustrated under ITER-relevant conditions. The parametric decay instability threshold power is shown to be substantially smaller than that of a single gyrotron beam.