First principles kinetic simulations of observed ion cyclotron emission driven by energetic ion-beams injected into LAPD

Ion cyclotron emission (ICE) is widely observed from minority energetic ion populations in toroidal magnetically confined fusion plasmas, both tokamaks and stellarators, and from cylindrical plasmas in the LAPD (Large Plasma Device). Comparing ICE spectra from LAPD and toroidal plasmas offers a unique pathway to identifying the influence, if any, of toroidal effects on the observed signal and on the underlying physics. Here we report first principles kinetic simulation of an ICE spectrum from a spiraling ion beam in the LAPD plasma, using the fully gyro-orbit-resolved particle-in-cell code EPOCH in 1D3V slab geometry mode. A simulated proton beam is found to relax collectively under the magnetoacoustic cyclotron instability, in a deeply sub-Alfvenic regime which is predominantly electrostatic. The simulated ICE power spectrum, obtained from the spatiotemporal Fourier transform of the excited field, quantitively captures the key features of the observed spectrum. These include downshifting of sequential narrow spectral peaks with respect to lower integer cyclotron harmonics below the flattening of the fast Alfven wave (FAW) dispersion relation, a broad continuum feature around the lower hybrid frequency, and exact higher-integer cyclotron harmonic peaks.