PLASMA RESPONSE ON IMPURITY INJECTION IN W7-AS

In order to study impurity transport and radiation behavior nitrogen h as been injected into the scrape-off plasma of limiter-dominated disch arges by gas puffing or into natural magnetic islands at the plasma ed ge of separatrix-dominated discharges by a reciprocating erosion probe . Strong radiative plasma edge cooling with a reduction of the power f lux to the limiter could be obtained. The accompanied degradation of t he energy confinement and the observed decrease of the central electro n temperature can partly be explained by the reduction of the effectiv e heating power. At high plasma densities and sufficiently strong impu rity injection phenomena well known from tokamaks, like plasma shrinki ng, plasma detachment from the limiters and MARFE's were transiently o bserved.