Penetration Studies for Deuterium Pellets in Wendelstein 7-AS

Deep particle fueling into a fusion-relevant plasma can be performed by the injection of cryogenic hydrogen or deuterium pellets. However, the penetration depth and fueling efficiency can be greatly limited when enhanced pellet ablation by fast particles occurs. Only a limited database exists for the penetration depth of ice pellets into stellarators. The penetration depth is measured during pellet injection into purely electron cyclotron resonance heated plasmas on the Wendelstein 7-AS (W7-AS) stellarator. These data are compared with the International Pellet Ablation Database (IPADBASE). Good agreement is found, if the neutral gas shielding model is applied for the scaling law of the penetration depth. The experimental data from W7-AS are used as a basis for planning a new pellet injection system for the Wendelstein 7-X stellarator, which is now under construction.