Identification of Minority Ion-Cyclotron Emission during Radio Frequency Heating in the JET Tokamak

First measurements and identification of minority ion-cyclotron emission (MICE) during ICRF (H)D minority heating in the JET tokamak are presented. An inner wall radiofrequency (rf) probe shows the new single MICE spectral line, down-shifted from the heating frequency and appearing $\sim 400\mathrm{ms}$ after the ICRH switch-on. The line is narrow $(\Delta \omega /\omega \approx 0.04)$, characterized by the ion-cyclotron frequency of minority protons in the outer-edge midplane plasma and is observed irrespective of whether single or multifrequency ICRH is applied. The observations are consistent with the classical evolution and population of the plasma edge with $\sim 3\mathrm{MeV}$ ICRH protons on orbits near the outboard limiters. Particle loss and energy filtering contribute to a local non-Maxwellian energetic ion distribution, which is susceptible to ion-cyclotron instability.