Rotation studies in fusion plasmas via imaging X-ray crystal spectroscopy

Abstract

The increase in plasma performance associated with turbulence suppression via flow shear in magnetically confined fusion plasmas has been well documented. Currently, the standard methods for both generating and measuring plasma rotation involves neutral beam injection (NBI). In the large, high density plasmas envisaged for next generation reactors, such as ITER, NBI will be considerably more difficult than in current experiments. As a result, there is a need to identify alternative methods for generating and measuring plasma flows. In an effort to meet these needs, a high resolution x-ray crystal spectrometer capable of making spatially resolved measurements has been designed, built, installed and operated on the Alcator C-Mod tokamak. By taking advantage of toroidal symmetry and magnetic flux surface mapping it is possible to perform spectral tomography with a single fan of views. This combination of spatially resolved spectra and tomographic techniques has allowed for local measurement of a number of plasma parameters from line integrated x-ray spectra for the first time. In particular these techniques have been used to measure temporally evolving profiles of emissivity, charge state densities, rotation velocities, electron temperature, ion temperature, as well as radial electric field over most of the plasma cross section (r/a < 0.9). In this thesis three methods for the generation of flows without the use of NBI are identified; intrinsic rotation in enhanced confinement modes, lower hybrid wave induced rotation and ICRF mode conversion flow drive. Each of these methods is discussed in detail with reference to how they might be used in next generation tokamaks.