Ion Cyclotron Emission on the DIII-D Tokamak

Observations of Ion Cyclotron Emission (ICE) on DIII-D show its potential as a tool to diagnose energetic particle behavior in future reactors [Dendy, et al., Phys. Plasmas 1, 3407 (1994), McClements, et al., Nucl. Fusion 55, 04013 (2015)]. ICE is readily excited across a wide region of DIII-D operational space by kinetic instabilities at the main ion species cyclotron frequency and its harmonics. A large set of ICE measurements on the DIII-D tokamak has been collected in 2015-17 with ICRF antenna straps configured as receiving antennas, and also with dedicated magnetic probes; each channel is digitized at 200 MSamples/sec for 5 seconds on each discharge. ICE is observed at harmonics of the main ion w_ci. It is strongest in NBI-heated plasmas with a clear dependence on beam geometry. ICE is detected in all DIII-D deuterium plasmas, but it is only observed in helium plasmas in H-mode conditions.  ICE most often originates from the outboard-edge in beam-heated H-mode discharges, possibly destabilized by the steep edge density gradient. However, ICE is also observed at low levels in plasmas without a significant fast ion population, such as Ohmic or electron-cyclotron-heated plasmas.  Relatively weak centrally-resonant ICE is detected in NBI-heated L-mode plasmas, including plasmas with negative triangularity. ICE responds promptly to transient MHD events, including ELMs, fishbones and sawteeth. A quantitative understanding of the relationship between ICE and the energetic particle distribution would be an important diagnostic advance since passive measurements of ICE in a burning plasma environment, such as ITER, could provide key information on the alpha particle population and fast-ion losses [D’Inca, et al., IAEA FEC Proceedings 2014]. This work on DIII-D establishes a large database, which is suitable for the creation of a synthetic diagnostic capable of extracting quantitative ion distribution information from ICE measurements.