JET experiments to assess the clamping of the fast ion energy distribution during ICRF heating due to finite Larmor radius effects

Experiments have been performed on the JET tokamak with 2nd harmonic ion cyclotron resonance heating (ICRH) of hydrogen in deuterium plasmas to assess the role of finite Larmor radius (FLR) effects on the resonant ion distribution function. More specifically, the clamping of high-energy resonant particle distribution due to weak wave-particle interaction at high energy is studied. The distributions of ICRH heated hydrogen ions have been measured with a high-energy neutral particle analyser in the range of 0.29-1.1 MeV. By changing the electron density the energy E*, around which the wave-particle interaction becomes weak, is varied. The dependence of the ion distribution on E* is experimentally observed for a number of discharges and FLR effects are clearly seen to affect the high energy tail shape. Experiments have been analysed with the combination of ICRH modelling codes PION and FIDO, including FLR effects, and good agreement with measurements have been found.