Fast-Ion Profiles in MHD-Quiescent Plasmas

The fast-ion distribution is measured using the fast-ion $D_\alpha$ (FIDA) diagnostic [1,2], which has spatial resolution of $\sim$5 cm, time resolution of $\sim$1 ms, and energy resolution of $\sim$10 keV. This paper focuses on the measurements under quiescent discharge conditions (i.e. in the absence of MHD activity and collective particle effects). A weighted Monte Carlo simulation code allows direct comparison of classical calculations of the fast-ion distribution function using either the TRANSP code or a Fokker-Planck code with the FIDA measurements. Pitch angle scattering and slowing down of fast ions are studied by varying the injection energy, beam angle, plasma density and electron temperature; the FIDA signals vary as classically expected in these MHD-quiescent plasmas. In addition, the fast-ion profiles are compared during co- and counter-injection of neutral beam. Neutral particle and neutron diagnostics corroborate the FIDA measurements. \par\vskip6pt\noindent [1] W.W. Heidbrink, et al., Plasma Phys. Control. Fusion \textbf{46}, 1855 (2004). \par\noindent [2] Y. Luo, et al., Rev. Sci. Instrum. \textbf{75}, 3468 (2004).