First observations of two-type energetic particle-driven ion cyclotron emission in MAST-U
The first measurements of energetic particle-driven ion cyclotron emission (ICE) in the Mega-Amp Spherical Tokamak Upgrade (MAST-U) have been obtained by adding a high sampling rate (250MHz) capability to one coil of the existing OMAHA array, oriented to measure fluctuations in the toroidal magnetic field component. All these measurements were carried out in pulses with either on-axis neutral beam injection (NBI) only, or a combination of on-axis and off-axis NBI. Two types of energetic particle-driven ICE have been detected: a narrow band emission with some frequency splitting at harmonics of the on-axis deuterium cyclotron frequency, fcD , and a broader-band emission harmonically-structured with peak frequencies corresponding to the harmonics of fcD at the outboard (low field side) plasma edge.