Coupling between JET Pedestal ne-Te and Outer Target Plate Recycling: Consequences for JET ITER-Like-Wall Operation

With the tungsten target plates of the JET ITER-Like-Wall (ILW) phase, carbon radiation will be reduced and must be replaced by that of seeded impurities to prolong target plate lifetime. Investigations to this end of ELMy-H (EH) & Advanced Tokamak (AT) scenarios using N2 and Ne along with D2 fuelling have been carried out in matrix fashion, whereby the aim was to cover a large variation in divertor power loading Pdiv and temperature Tediv regardless of core performance. The intended effect of impurity seeding is to increase radiation Prad in order to mitigate Pdiv and that of D2 to enhance recycling to further reduce Tediv, both being necessary for ILW-compatibility. Prad/Pin ranged over 48-66% (EH) and 31-60% (AT). Details on Prad and Pdiv are given in a companion paper. This data set is used to study the interrelationships between the pedestal temperature Teped & density neped and the ion flux Gi to the outer target plate. An advantage of these studies is the wider range of neped and Teped afforded by the use of impurities. Different type-I ELM regimes also prevail: For EH, vELM initially decreases with D2 (~20->10Hz). Impurities can provoke compound ELMs (vELM 3Hz) as well as augment vELM (to 50Hz).
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