Experimental comparison of ion cyclotron emission in the LHD stellarator and DIII-D tokamak

Ion cyclotron emission (ICE) is ubiquitously observed at integer harmonics of the cyclotron frequency of fast ions present in magnetic fusion devices such as tokamaks and stellarators. Due to the ease of detection, ICE has the potential to serve as a passive fast ion diagnostic suitable for harsh burning plasma environments, so long as this collective instability is sufficiently well understood. To this end, dedicated experiments have been performed on the LHD stellarator and DIII-D tokamak to determine the sensitivity of ICE to magnetic configuration, fast ion distribution and species (H and D), and fundamental plasma parameters including magnetic field strength, electron density, and the thermal ion species mix (H, D, and ³He). Whereas ICE in DIII-D is observed uniformly on all toroidally-separated probes, ICE in LHD exhibits a strong toroidal localization, indicating a major difference in eigenmode structure and propagation. In both tokamak and stellarator configurations, ICE is most commonly emitted near the plasma edge, though core emission is also possible in spherical tokamaks such as NSTX(-U) and L-mode DIII-D plasmas. The dependence of the saturated ICE amplitude on plasma parameters will be discussed.