New Interpretation of Ion Cyclotron Emission from a Tokamak

The tempting interpretation of Ion Cyclotron Emission (ICE) in terms of compressional Alfv´en eigenmodes involving energetic ions is inconsistent with recent TCV experimental observations in some important aspects, such as i) the perturbed poloidal field is exceeding the parallel perturbed magnetic field significantly, and ii) the modes are near cyclotron harmonic and exhibit Alfv`en scaling of their frequency. We show that these characteristics can be explained by considering finite Larmor radius effects of thermal ions in shear Alfv´en waves that allow such waves to exist well above the ion cyclotron frequency in the form of wavepackets bouncing within the plasma volume.