Variation of the particle confinement during neutral injection into ASDEX divertor plasmas

With neutral injection into ASDEX divertor plasmas the line average density generally decreases. Evidence is presented that the reduction in plasma content is partly caused by a reduction in particle confinement. The reduction in confinement affects the outer plasma zones first, and frequently, in conjunction with a sawtooth instability, impairs the plasma center too. The overall reduction in particle confinement is not caused by beam effects alone but appears to be correlated with profile changes of the heated plasma. The deterioration of the particle confinement does not seem to be an inevitable occurrence. There exists an operational regime where the density increases during the neutral injection pulse after first decreasing in the usual manner. Under these circumstances the density increase leads to high βsub(p) values of about 1.55 to 1.75 and a threefold enhanced neutron flux. The high βsub(p)-phase is periodically interrupted by gross instabilities in the outer plasma zones which cause sudden βsub(p)-reductions. (orig.)