Effects of deuterium-tritium mix on linear growth rates of the magnetoacoustic cyclotron instability in fusion plasmas

Spontaneously excited ion cyclotron emission (ICE) provides a passive diagnostic of the physics of energetic ions in most contemporary toroidal magnetically confined fusion plasmas. ICE is typically driven by spatially localized, strongly non-Maxwellian, energetic ion populations relaxing collectively under the magnetoacoustic cyclotron instability (MCI). Studies of the MCI in its linear and nonlinear regimes assist interpretation of observed ICE spectra in relation to the properties of the ion populations responsible. Here, we use the LinearMaxwellVlasov.jl (LMV) code to calculate linear MCI growth rates γMCI spanning two-dimensional wavenumber (k⊥,k∥) space, for parameters appropriate to the edge region of JET DT plasma 26148 from which widely studied ICE spectra, driven by marginally trapped 3.5 MeV fusion-born alpha-particles (see G. A. Cottrell, Nucl. Fusion, 33, 1365 (1993)), were obtained during the Preliminary Tritium Experiment (JET Team, Nucl. Fusion, 32, 187 (1992)). We extend the LMV code to include, for the first time, the two thermal ion species: tritium, in addition to deuterium alone, as addressed in previous studies of this code. Since the observed spectral peaks of ICE often correspond to the most strongly linearly unstable frequencies, this study is helpful for future DT plasma scenarios. Our results show that the dependence of γMCI on tritium concentration with respect to electron number density, ξT, is highly structured across (k⊥,k∥) wavenumber space. We identify systematic trends in the spectral properties of γMCI, notably the onset of doublet splitting of peaks and the frequency shifting of unstable modes as ξT is varied. These results are well anchored with respect to earlier, non-computationally enabled, analytical calculations of γMCI.