Particle-in-cell simulations of two plasmon decay in a non-monotonic density profile

Strong scattering during electron cyclotron resonance heating (ECRH) experiments in several magnetically confined fusion devices has been attributed to parametric decay instabilities (PDIs). Analytical modeling has shown that a non-monotonic density profile and excitation of trapped waves through two plasmon decay (TPD) play an important role. Using a particle-in-cell (PIC) code, decay of an X-mode wave into waves trapped inside a non-monotonic density profile is observed. The time evolution and composition of the daughter waves are investigated for different density profiles. A build up of the TPD daughter waves is only observed when they are supported by the plasma.