Towards a Predictive Model of Power Loss from Parametric Decay of ICRF Waves

Abstract. Both theory and experiment have suggested that parametric decay instability (PDI) is a possible edge power loss mechanism in ICRF (including HHFW and IBW) heating of tokamak plasmas. In this paper, we consider the extension of previous theoretical models to enable a quantitative evaluation of pump depletion and power loss due to PDI. A set of nonlinear coupled equations for a long-wavelength “dipole ” pump and short-wavelength daughter modes is derived. The model recovers the standard PDI dispersion relation for fixed pump wave amplitude, and obeys an appropriate nonlinear energy conservation law. When dissipation is present the model provides a description of energy flow from the pump to the daughter modes and the particles. The equations are intended to describe parametric decay and pump depletion in inhomogeneous plasmas. By writing the nonlinear coupling coefficients in terms of a spectral basis, a strategy for implementing the model in full-wave spectral codes is presented