IMPROVED CONFINEMENT WITH EDGE RADIATIVE COOLING AT HIGH-DENSITIES AND HIGH HEATING POWER IN TEXTOR

Improved confinement is achieved on TEXTOR under high power conditions (up to 4 MW of additional heating with NBI-co+ICRH, NBI-co+counter or NBI-co+counter+ICRH) with edge radiative cooling employing silicon or neon as the radiating impurities. It is shown that in quasi-stationary conditions up to 85% of the input power can be radiated. Such high power fractions offer the possibility of utilizing these techniques to facilitate the power exhaust problem for a tokamak reactor. Discharges with edge radiative cooling exhibit enhanced confinement properties at high densities, e.g. at a central line averaged electron density of 7.5 x 10(13) CM-3 , an enhancement factor of 1.7 over ITER L89-P confinement scaling is obtained with an edge q value as low as 2.7. Stable discharges have been obtained even with the q = 2 surface located inside the radiating zone. Furthermore, for radiatively cooled discharges heated with balanced NBI-co+ counter with or without ICRH, supershot-like peaked electron density profiles, with central density values above 1.0 X 10(14) CM-3, are observed. The present results show that there is no impurity accumulation in the centre and the Ne and/or Si concentration is so low that the reactivity of the plasma remains unaffected.