TF Ripple Effects on the NBI Deuteron Confinement in JET
This paper reports the effects of Toroidal magnetic Field (TF) ripple on the confinement of NBI-produced deuterons in recent JET experiments where an N=16 TF ripple harmonic was induced. The influence of an enhanced TF ripple on NBI deuterons is examined with a Neutral Particle Analyzer (NPA) in the 5­40keV energy range by analyzing the neutral deuterium fluxes formed by Charge eXchange (CX) and recombination of deuterium ions with energies well above the temperature of plasma deuterons. Due to the NPA line of sight, the observed flux is induced mainly by the charge exchange between neutrals and deuterium ions with Vll 0 at the plasma mid-plane: the measured fluxes characterize therefore the ions mostly affected by ripples. Such a reduction in the deuterium neutrals emitted from plasmas with an N=16 ripple harmonic was observed in previous ripple experiments at JET. The main purpose of this paper to report on an experimental study of the reduction in neutral deuterium (D0) flux and its dependency on the magnetic shear in the plasma core (as well as other plasma parameters) and on the magnitude of the N=16 TF ripple harmonic. Interpretive 3D Fokker-Planck modeling of the effect of TF ripple on the partly thermalized NBI deuterons contributing to measured D0 fluxes is in reasonable agreement with measurements.