Session RP1 - Poster Session VIII.
POSTER session, Thursday afternoon, October 30
Fran Hill Southeast Exhibit Hall, ACC
Initial estimates of particle transport in the quasi-helically symmetric stellarator, HSX, are carried out using a multichannel interferometer system which has 9 viewing chords with 1.5 cm spacing. Density perturbations are produced by modulating the plasma gas fuelling and the particle source is measured by a multi-channel Ha system. The total radial particle flux is estimated by solving the continuity equation. Diffusion coefficient D and convection velocity V are modeled. Preliminary estimates indicate a diffusion coefficient De\sim1 m2/s. Investigation of fast oscillations evident on the interferometer time-series traces reveals the existence of high-frequency density fluctuations in the range of 25-100 kHz. These fluctuations are noted to have an m=1 nature and are only observed in quasi-helically symmetric plasmas in HSX. Observation of these fluctuations is made during the ECRH pulse when the resonance position is near the plasma core suggesting they may be driven by gradients in the plasma pressure.