Threshold of parametric decay instability accompanying electron   Bernstein wave heating in spherical tokamaks
  The parametric instability of upper hybrid wave decay into back scattered upper hybrid wave and lower hybrid wave is considered for conditions of inhomogeneous plasma of spherical tokamaks. The possibility of absolute instability is demonstrated and the corresponding threshold is determined. It is shown that the threshold power increases with pump frequency and electron temperature. Threshold power is estimated for typical parameters of experiment in MAST tokamak. It is shown that in this case parametrical reflection arises, if probing power exceeds 90W/cm^2, which gives 30 kW for a beam of 10 cm radius. 
Evgeniy Gusakov (HTPPL), Alexander Surkov (HTPPL)