Suprathermal deuterium ions produced by nuclear elastic scattering of ICRH driven He3ions in JET plasmas

Measurements of the suprathermal tail of the energy distribution function of deuterium ions, in plasmas containing MeV energy ICRH driven minority He 3 ions and majority deuterium ions, revealed that the suprathermal tail ion density exceeded by nearly an order of magnitude that expected due to nuclear elastic scattering (NES) of He 3 projectile ions on deuterium target ions. The experiments were performed on the Joint European Torus (JET), measurements of the line-of-sight integrated energy distribution functions of He 3 and suprathermal deuterium ions were made using a high energy neutral particle analyzer. The NES or 'knock-on' deuterium ion energy distribution function was simulated using the FPP-3D Fokker–Plank code (Zaitsev et al 2002 Nucl. Fusion 42 1340 ) which solves the 3D trajectory averaged kinetic equations in JET tokamak geometry while taking into account NES of He 3 ions on the deuterium ions. The required input energy distribution function of ICRH driven He 3 ions was simulated using the SELFO code (Hedin et al 2002 Nucl. Fusion 42 527 ). The comparison between measurement and simulation in the He 3 ICRH experiments is contrasted with an analogous previous comparison between measurements and simulation of JET plasmas in which 3.5 MeV DT fusion alpha-particles were the projectile ions, where measurement and simulation roughly agreed. Possible explanations for the observed excess knock-on deuterium tail in the experiments with He 3 minority ICRH are discussed. The importance of D + He 3 fusion products as additional drivers of suprathermal fuel ions is underlined.