Speaker
Description
Collective Thomson scattering (CTS) diagnostics have been installed at several machines and will be primary alpha-particle diagnostic at ITER. CTS measurements are sensitive to the projection of the local velocity distribution function in a measurement volume. The thermal ions with low projected velocities dominate the low-Doppler-shift part of CTS spectra whereas the fast ions with high projected velocities dominate the high-Doppler-shift parts. The projection determines to which extent a given region in fast-ion phase- and velocity-space contributes to a given spectral bin of a CTS spectrum. Here, we discuss the formation of the high-Doppler-shift parts of CTS spectra as well as the corresponding weight functions that quantify the velocity- and phase-space sensitivities. The weight functions can be split into a rate part that depends only on the frequency or, equivalently, the projected velocity, and a projection part from either 2D velocity space or 3D phase space. CTS weight functions allow rapid interpretation of CTS spectra and the inversion of CTS spectra in velocity space or phase space in conjunction with other energetic particle diagnostics.