PELLET INJECTION WITH IMPROVED CONFINEMENT IN ASDEX
Tokamak discharges with repetitive pellet fuelling were investigated in the ASDEX divertor device. The importance of sufficiently high divertor recycling for successful density build-up in the bulk plasma was demonstrated. In OH heated discharges with high recycling an energy confinement time of 160 ms was reached, the normal values being 80 ms in the roll over region. The peaked density profiles in these cases were accompanied by reduced or suppressed sawtooth activity and finally ended in a phase of strong central impurity accumulation. The particle transport was characterized by strong, non classical inward drift, while the improved energy transport can be explained by two alternatives: (1) a local model which assumes neo Alcator Xe for the electrons and an Xi- = 3-Xneocl for the ions in the gas puff cases reduced to Xi- + Xneocl for the optimum pellet cases; (2) a profile consistency picture where T-e(a) determines the energy confinement. Low power, NI heated discharges with pellet fueling behave like ohmic discharges, while for high power in the L-mode no successful density build-up was possible, and tau-E was not improved. The H-regime was extended to n-e = 1.2.1020m-3 by the injection of pellets. In this case a density build-up takes place, but a further density profile peaking could not be observed.
Bibliographic Reference: WRITE TO MAX-PLANCK-INSTITUT FUER PLASMAPHYSIK, 8046 GARCHING BEI MUENCHEN (GERMANY), MENTIONING REPORT IPP 1/242, 1987
Record Number: 1989126025001 / Last updated on: 1989-01-01
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