Dimensionless Pedestal Identity Plasmas on Alcator C-Mod and JET

Properties of the H-mode pedestal are crucial for standard (Q = 10) operating regimes envisaged for ITER, but their scalings remain uncertain. Conflicting evidence exists for the variation of density pedestal width Dne, which can be governed by particle sources on DIII-D and MAST, but is more strongly affected by plasma transport on Alcator C-Mod [3,4] and ASDEX Upgrade. Further insight has been sought by producing plasmas on C-Mod and JET in a common single-null divertor equilibrium and with identical values of dimensionless variables n*eped, r*ped, bped, q95 at the pedestal top; this ensures local plasma transport is the same while stringently testing other susceptibilities through a ratio aJET/aC-Mod > 4 in absolute size plus markedly different recycling regimes. Accurate realisation of the chosen magnetic configuration on both machines is illustrated by the overlay of scaled separatrices in Fig.1. Edge dimensionless identity then requires (as well as equal mi/me, Zeff) discharge parameters to be scaled as indicated in Table 1 . Time intervals on each device can similarly be related according to (tB-tA)C-Mod (tB-tA)JET (aC-Mod/aJET)5/4 .
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EFDC080324 317.55 Kb