The effect of species mix and fast-ion distribution on emission of fast magnetosonic waves near the ion cyclotron frequency*

In the radiation belts, energetic ions drive wave emission both above and below the ion cyclotron frequency $\omega_{\mathrm{ci}}$. In a Frontier Science experiment on the DIII-D tokamak, emission of fast magnetosonic waves near $\omega_{\mathrm{ci}}$ and its harmonics is investigated using systematic scans of species mix, magnetic field, and fast-ion distribution function. For most fast-ion populations, increasing H$^{\mathrm{+}}$ in a background D$^{\mathrm{+}}$ plasma increases emission below $\omega _{\mathrm{ci\thinspace }}$but decreases emission above $\omega _{\mathrm{ci}}$, while lower magnetic field strength gives stronger emission below $\omega_{\mathrm{ci}}$ but has relatively little effect above $\omega_{\mathrm{ci}}$. Addition of a third species ($^{\mathrm{3}}$He$^{\mathrm{++}})$ sometimes introduces an additional emission band below $\omega_{\mathrm{ci}}$ reminiscent of the three electromagnetic ion cyclotron wave bands of H$^{\mathrm{+}}$, He$^{\mathrm{+}}$, and O$^{\mathrm{+}}$ in space. For higher frequencies ($\omega $\textgreater $\omega_{\mathrm{cH}})$ fast magnetosonic waves with spectral peaks at multiples of $\omega_{\mathrm{cH\thinspace }}$have been observed by satellites in the equatorial magnetosphere. Similar spectra at harmonics of $\omega_{\mathrm{ci}}$ are observed in magnetically confined fusion plasmas. Comparisons of stability calculations used in both the space and fusion communities will be shown.