Interpreting ion cyclotron emission associated with transient events in Large Helical Device deuterium plasmas

Ion cyclotron emission (ICE), driven by fast collective relaxation of energetic ion populations, has been detected from most large magnetic confinement fusion plasmas. ICE is suprathermal, with narrow spectral peaks that can be mapped to the cyclotron harmonics of energetic ion species in the emitting region. Advances in the RF diagnostics in the LHD heliotron-stellarator enable time-resolved ICE measurements during transient, bursty, plasma events that evolve on microsecond timescales. Recent ICE measurements from LHD deuterium plasmas suggest that ions born in DD fusion reactions, in addition to neutral beam injected ions, may generate ICE during bursty events. A distinctive feature is the role of apparent large Doppler frequency shifts comparable to the separation between ICE peaks. Using a particle-in-cell hybrid code to simulate the relaxation of one or more energetic ion species within deuterium plasma under the self-consistent Maxwell-Lorentz system of equations, we find that the magnetoacoustic cyclotron instability drives the ICE. The transient event can cause rapid evolution of the energetic ion distribution in real and velocity space, and of the ambient plasma. We describe how the foregoing physics can be integrated into a model for ICE from transient events in LHD.