Stabilization of low-threshold two-plasmon parametric decay instability with oblique microwave incidence on the plasma

It is shown that, when a pump extraordinary wave is obliquely incident onto the plasma in the electron cyclotron resonance heating (ECRH) experiments, an increase takes place in the threshold of parametric decay instability (PDI) leading to generation of two localized upper-hybrid waves. It is proposed to use a small tilt of the heating beam to suppress this PDI which is most dangerous and often observed in the ECRH experiments.