Ion cyclotron emission as a future diagnostic for reactivity in aneutronic fusion plasmas*

Reactivity within aneutronic plasmas will not be measurable by neutron diagnostics used in DT and pure deuterium plasmas. Hence, we examine the potential of ion cyclotron emission (ICE) from fusion-born protons in aneutronic plasmas as an alternative diagnostic approach. ICE is well adapted for two reasons (a) measurements of ICE have revealed the presence of trace quantities of confined fusion-born 3.0 MeV protons in pure deuterium plasmas where their presence was not anticipated, and (b) ICE scales linearly with fusion reactivity as observed from DT fusion-born 3.5 MeV alpha-particles in JET and TFTR. First principle simulations using the PIC code EPOCH have assisted recent ICE observations. EPOCH fully resolves gyromotion, and hence captures resonant phenomenology underlying ICE, the magnetoacoustic cyclotron resonance, which is generated by the relaxation of strongly non-Maxwellian energetic ion populations. We present EPOCH simulations of 14.7MeV proton driven ICE as a result of the fusion between thermal deuterium and helium-3 ions. For continuity to previous studies, we assume: JET-type plasma parameters for the location at which ICE is generated; an energetic proton perpendicular velocity component comparable to the Alfvén speed; and the velocity-space initialisation of protons as a drifting ring-beam. The energetic protons’ large parallel velocity component acts as a corollary to the DT alpha-particles and DD protons, and has unique consequences for the obtained simulated ICE spectra.