Calculations of instabilities with frequencies above the ion cyclotron frequency in DIII-D plasmas*

In the earth’s radiation belts, energetic ions drive waves called “equatorial noise” at frequencies above the the ion cyclotron frequency. In tokamaks, similar instabilities are called ion cyclotron emission. An experiment on the DIII-D tokamak varied the energetic ion populations and plasma composition. The energetic ion populations were altered by injecting neutral beams at different angles, with different energies, and different species (H and D). The observed stability properties are compared with simulations [1] that solve the magnetoacoustic wave dispersion relation in a spatially uniform plasma. In the code, multiple model distribution functions are combined to accurately approximate the actual distribution functions.

 

[1] J.W.S. Cook, Pl. Phys. Cont. Fusion 64 (2022) 115002.