Effect of spatial and velocity distributions on the generation of ion cyclotron emission from fusion products

Abstract

Cyclotron motion of fusion products (FPs) or other superthermal ions has been shown theoretically to generate ion cyclotron emission (ICE) which is strongly dependent upon the ratio of ion velocity to the background Alfvén velocity [C. Chu and J. L. Sperling, J. Plasma Phys. 40, 40 (1988)]. This initial work described ICE assuming a uniform plasma embedded in a constant magnetic field; in addition, a delta function velocity distribution was used for the superthermal ions. These assumptions lead to ICE spectra which exist as a series of delta functions at harmonics of the fundamental cyclotron frequency of the superthermal species. It is shown here that source distributions with finite spatial extent such as a higher order parabolic model ((S(R)=S0{1−[(R−R0) /a]2}N,N=6–10)), in conjunction with the magnetic field profile ((B(R)=B0R0 /R)), lead to a significant broadening of the ICE spectra; this is the case even for a delta function velocity distribution. The spectra are further modified when realistic superthermal distributions are employed in the model. In the latter case, a Green’s function approach is employed to calculate the spectra. Results of the ICE calculations are presented for FP protons.