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B. LaBombard, J.E. Rice, A.E. Hubbard, J.W. Hughes, M. Greenwald,
R.S. Granetz, J.H. Irby, Y. Lin, B. Lipschultz, E.S. Marmar, K. Marr,
D. Mossessian, R. Parker, W. Rowan, N. Smick, S.M. Wolfe and S.J. Wukitch
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The dependence of L-H power threshold on magnetic topology (upper-,
lower-null) in a tokamak is linked to near-sonic plasma flows in the high-field
side scrape-off layer. Scrape-off layer flow momentum, coupling across the
separatrix, imparts a topology-dependent increment to edge and core toroidal
rotation (counter-, co-current). In all topologies, rotation increases in
the co-current direction with input power: the L-H transition is seen when
co-rotation achieves a characteristic level. Correspondingly, higher power
is required to attain H-modes in upper- versus lower-null (with BxGradB
down). |
