Impurity shielding and sweeping-out by an axisymmetric divertor in DIVA

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Abstract
A pulse of methane gas and a short burst of aluminium have been injected into DIVA plasma at the point farthest from the divertor. For the same amount of injected impurity, the accumulation of injected impurity in the main plasma is reduced by a factor of 2 to 4 by the action of the divertor. The impurity shielded by the scrape-off plasma is rapidly guided into the burial chamber. The time needed for the poloidal excursion of the injected impurity ions in the scrape-off layer is roughly equal to that of the scrape-off plasma. Sweeping-out of the impurity ions diffusing from the main plasma into the burial chamber is also observed.