Mechanisms for impurity control in JET

Control of the influx of high Z material is examined for a one-dimensional plasma transport model that includes the effects of a scrape-off layer to determine the edge boundary conditions; the scrape-off layer is assumed to be formed in the shadow of a limiter. The introduction of a specified influx of low Z material when the limiter is made of a high Z material and the replacement of this limiter by one of a low Z material are found to be equally effective in controlling the plasma edge temperature, and hence the influx of high Z material, with the subsequent establishment of a CPW and an acceptably large aperture for the hot central plasma. (orig./AH)