A Investigation of Particle Transport Through the Measurement of the Electron Source in the Texas Experimental Tokamak
The spatial distribution of the electron source has been measured spectroscopically in the Texas Experimental Tokamak. The method used involves the measurement of the emissivity of the Balmer (alpha) and (beta) lines of neutral hydrogen. Modelling of the corresponding atomic transitions provides a relation between the emissivities and the electron source from the ionization of neutrals. Toroidal distributions were obtained by means of a set of relatively calibrated photodiode-amplifier-filter packages referred to as plasma light monitors. Such monitors were distributed toroidally, and attached primarily to radial ports. Specially constructed, absolutely calibrated monitors provided absolute calibration. A scanning, rotating mirror system provided in-out brightness profiles. A TV camera system, viewing the limiter through a tangential port, provided a qualitative description of the poloidal asymmetry. Such description was necessary for the inversion of the rotating mirror data. Using electron density profiles obtained by means of far-infrared interferometry, and integrating the electron sources, the global particle confinement time ((tau)(,p)) was computed. Parameter scans were performed in ohmically heated plasmas, varying the toroidal field (1.5T (LESSTHEQ) B(,t) (LESSTHEQ) 2.8T), the plasma current (100kA (LESSTHEQ) I(,p) (LESSTHEQ) 400kA), the electron density (1 x 10('-13)cm('-3) (LESSTHEQ) n(,e) (LESSTHEQ) 9 x 10('13)cm('-3)), and the plasma position (-3cm (LESSTHEQ) (DELTA)R (LESSTHEQ) +3cm) with respect to the center of the poloidal ring limiter. It was found that (tau)(,p) peaks for a critical density that is independent of the other parameters. The particle confinement time was observed to decrease with increasing toroidal field, and to increase with increasing plasma current. An enhancement of the particle confinement was observed when the plasma column is displaced from the center of the limiter toward the outer wall. On the other hand, the confinement time decreases when the plasma is displaced inward.
- Pub Date:
- Physics: Fluid and Plasma