Temporal evolution of confined fast-ion velocity distributions measured by collective Thomson scattering in TEXTOR
S. K. Nielsen, H. Bindslev, L. Porte, J. A. Hoekzema, S. B. Korsholm, F. Leipold, F. Meo, P. K. Michelsen, S. Michelsen, J. W. Oosterbeek, E. L. Tsakadze, G. Van Wassenhove, E. Westerhof, and P. Woskov

Fast ions created in the fusion processes will provide up to 70 \% of the heating in ITER. To optimise heating and current drive in magnetically confined plasmas insight into fast ion dynamics is important. First measurements of such dynamics by collective Thomson scattering (CTS) were recently reported [Bindslev et. al, PRL $\mathbf{97}$, 205005, 2006]. Here we extend the discussion of these results which were obtained at the TEXTOR tokamak. The fast ions are generated by neutral beam injection and ion cyclotron resonance heating. The CTS system uses 100--150 kW 110 GHz gyrotron probing radiation which scatters off the collective plasma fluctuations driven by the fast ion motion. The technique measures the projected 1D velocity distribution of confined fast ions in the scattering volume where the probe and receiver beams cross. By shifting the scattering volume a number of scattering locations and different resolved velocity components can be measured. The temporal resolution is 4 ms while the spatial resolution is $\sim$10 cm depending on the scattering geometry. Fast ion velocity distributions in a variety of scenarios are measured, including the evolution of the velocity distribution after turn off of the ion heating. These results are in close agreement with numerical simulations.

© 2008 The American Physical Society.