PPPL-3574 is available in pdf or postscript formats.

Transient Transport Experiments in the CDX-U Spherical Torus

Authors: T. Munsat, P.C. Efthimion, B. Jones, R. Kaita, R. Majeski, D. Stutman, and G. Taylor

Date of PPPL Report: June 2001

Published in: Physics of Plasmas 9 (February 2002) 480-487

Electron transport has been measured in CDX-U using two separate perturbative techniques. Gas modulation at the plasma edge was used to introduce cold-pulses which propagate towards the plasma center, providing time-of-flight information leading to a determination of ce as a function of radius. Sawteeth at the q = 1 radius (r/a ~ 0.15) induced heat-pulses which propagated outward towards the plasma edge, providing a complementary time-of-flight based ce profile measurement. This work represents the first localized measurement of ce in a spherical torus. It is found that ce = 1-2 m2/sec in the plasma core (r/a < 1/3), increasing by an order of magnitude or more outside of this region. Furthermore, the ce profile exhibits a sharp transition near r/a = 1/3. Spectral and profile analyses of the soft X-rays, scanning interferometer, and edge probe data show no evidence of a significant magnetic island causing the high ce region.