Fast-ion distributions from third harmonic ICRF heating studied with neutron emission spectroscopy

Abstract

The fast-ion distribution from third harmonic ion cyclotron resonance frequency (ICRF) heating on the Joint European Torus is studied using neutron emission spectroscopy with the time-of-flight spectrometer TOFOR. The energy dependence of the fast deuteron distribution function is inferred from the measured spectrum of neutrons born in DD fusion reactions, and the inferred distribution is compared with theoretical models for ICRF heating. Good agreements between modelling and measurements are seen with clear features in the fast-ion distribution function, that are due to the finite Larmor radius of the resonating ions, replicated. Strong synergetic effects between ICRF and neutral beam injection heating were also seen. The total energy content of the fast-ion population derived from TOFOR data was in good agreement with magnetic measurements for values below 350 kJ.

Fast ion energy distribution from third harmonic radio frequency heating measured with a single crystal diamond detector at the Joint European Torus

“…(33) enhancement reflects the acceleration of beam ions to energies of a few MeVs, where the cross section for dd neutron emission is about an order of magnitude higher than that at typical JET beam energies (about 100 keV). This significant increase in neutron emission is a known feature of this heating scenario 5,8 and was observed in each of the three discharges considered in this analysis. Figure 4 shows the corresponding energy deposition spectrum measured by the SDD and integrated over the whole heating phase.…”

“…23 This scenario, which is particularly effective at accelerating deuterium ions to the MeV range as previously demonstrated, 5,24,25 is of relevance for fast ion physics studies in a deuterium plasma. Here, we show, in particular, that SDD data can be used to extract parameters of the highly non-Maxwellian fast ion energy distribution generated in the experiment by detailed modeling of the instrument response function and the emission spectrum of the fusion neutrons born in the plasma.…”

“…This interaction, which is typically not important to understand data from a deuterium plasma heated by neutral beam injection (NBI) only, must be accounted for in the case of third harmonic ICRH, where the reactant ions can be accelerated to few MeVs. 5,23,24 The resulting signature in the response function is illustrated, together with multi-scattering, by the difference between the solid and dashed curves of Figure 1 at E n = 6.05 MeV.…”

“…They can be used to extract essential parameters for machine control, such as the fuel ion temperature, 1 the thermal/non-thermal components of the neutron emission, 2,3 and the fuel ion ratio. 4 More recently, they have contributed to fundamental studies on the physics of suprathermal ions in thermonuclear plasmas, mostly by detailed measurements of the distribution function of the energetic ions [5][6][7] and their effects on the plasma stability. 8,9 Advanced neutron spectroscopy measurements are nowadays performed along a single, collimated line of sight by means of dedicated, non-compact detectors, based on the time of flight technique [10][11][12] for deuterium-deuterium (dd) fusion neutrons and on proton recoil for deuterium-tritium (dt).…”

High-definition velocity-space tomography of fast-ion dynamics

“…true true sim (13) The goal is now to reconstruct ∆F true , given synthetic measurements of F true in five FIDA views and F sim . We add 5% Gaussian noise to each synthetic measurement which is a realistic noise level for FIDA measurements at ASDEX Upgrade.…”