Recently-developed methods are used successfully to reconstruct the two-dimensional velocity-space distribution of the energetic minority MeV ion tail created by heating in the ion cyclotron range of frequencies (ICRFs) in the D–D–3He three-ion scheme. This reconstruction is based on neutron emission spectroscopy and gamma-ray spectroscopy measurements of JET plasma 95679. These datasets present challenges in velocity-space tomography which are met by collisional regularisation coupled to a sparsity-promoting regularisation technique. In combination, these capture the energetic ion tail in pitch-angle as well as in energy. Our reconstructions highlight the importance of diagnostics that can probe the plasma with oblique lines-of-sight with respect to the direction of the confining magnetic field. Our inferred fast-ion distribution corroborates experimentally the pitch angle tilt of the energetic ion tail predicted analytically, and by TRANSP simulations, for the three ion ICRF scheme. The synergies between neutral-beam injection and ICRF heating are captured by these diagnostics, and we are able to validate models of electromagnetic ICRF wave heating directly from the experiments.
This paper describes the reconstruction of the 2D velocity-space distribution of energetic minority MeV ions created by ion cyclotron range of frequencies (ICRF) heating in a D-D-3He three-ion scheme at the JET tokamak. The reconstruction is based on neutron and gamma-ray spectroscopy measurements and uses advanced tomography techniques to capture the energy and pitch-angle distribution of the fast-ion tail.