Calibration of the upgraded motional Stark effect diagnostic on TFTR

The q profile plays a key role for plasma equilibrium and theories of magnetohydrodynamic instabilities. With the development of the motional Stark effect (MSE) diagnostic, accurate q(r,t) profiles have been measured and utilized for equilibrium and stability analysis. Improvements to the MSE diagnostic on TFTR include a new method for calibrating the system and increasing the number of sightlines from 12 to 21 channels. A technique that uses the known poloidal field at the edge of the plasma is utilized to calibrate each sightline. The major radius is moved over the course of a discharge such that the plasma edge covers each sightline radius. Then with several discharges at various plasma currents each channel is independently calibrated. This method has been compared to our earlier calibration technique using neutral beam injection into a gas filled torus and some differences in the calibration have been found that have been attributed to differences in the excitation and l mixing processes in the Stark spectrum. copyright 1997 American Institute of Physics