Stability analysis of runaway-driven waves in a tokamak

Runaway electrons (REs) generated during disruption events in tokamaks have to be mitigated to minimize the detrimental impact from their massive losses to the wall, especially in ITER. RE-driven micro-instabilities, such as whistlers and magnetized plasma waves, can cause enhanced RE scattering and thereby alleviate the mitigation problem. This work presents a newly developed ray-tracing code COIN which enables stability analysis of runaway-driven waves in a tokamak. The code uses a standard ray-tracing procedure to calculate a wave-packet trajectory in a realistic plasma equilibrium and integrates the runaway kinetic drive and collisional damping of the wave. This approach captures convective aspects of wave amplification, such as the evolution of the wave vector due to plasma non-uniformity and internal reflection of the wave from the plasma boundary. An illustrative ray-tracing calculation of the instability threshold is presented for ITER-like parameters.