Alcator C-Mod

Alex Ince Cushman

Working Thesis Title: Momentum Transport Studies on Alcator C-Mod

Thesis Advisor: J.E. Rice

Thesis Reader: I.H. Hutchinson

In recent years there has been increased interest in understanding plasma rotation in tokamak discharges. Experimental and theoretical evidence suggest that plasma rotation and shear (particularly in the edge region) play an important role in a number of processes including turbulence suppression, L-mode to H-mode transitions, and internal transport barrier formation.

Although a tremendous amount of effort has been put into understanding particle and energy transport, relatively little work has been done on momentum transport. Experiments on a number of different tokamaks have shown that plasmas with little or no external momentum input can rotate quite strongly. More over, in high confinement regimes, all plasmas seem to rotate in the co-current direction with the rotation scaling with stored energy. Understanding the mechanisms that give rise to this intrinsic rotation may have has implications for next generation tokamaks like ITER. For example, if we can predict/control the intrinsic rotation then it may be possible eliminate the need for active stabilization of resistive wall modes.

To study momentum transport in a plasma it is necessary to make velocity measurements. One way to measure rotation velocities in a plasma is to measure the Doppler-shift of impurity emission lines. A variety of high resolution x-ray spectrometers have been installed on Alcator C-Mod to make such measurements.

The goal of this thesis is to gain a better understanding of intrinsic rotation through a combination of theoretical and experimental work.