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(EX5/6) Cross-Field Transport in the SOL: Its Relationship to Main Chamber and Divertor Neutral Control in Alcator C-Mod

B. Lipschultz¹⁾, B. LaBombard¹⁾, J. A. Goetz¹⁾, C. S. Pitcher¹⁾, N. Asakura²⁾, R. L. Boivin¹⁾, J. Hughes¹⁾, A. Kallenbach³⁾, G. M. McCracken⁴⁾, G. Matthews⁴⁾, D. Mossessian¹⁾, J. Rice¹⁾, J. L. Terry¹⁾, M. Umansky^5)
 
1) M.I.T. Plasma Science and Fusion Center, 175 Albany St., Cambridge, MA 02139 USA
²⁾ Japan Atomic Energy Research Institute, Naka-Machi, Naka-gun, Ibareki-ken, Japan
³⁾ MPI für Plasmaphysik, EURATOM Association, D-85748 Garching, Germany
⁴⁾ UKAEA Fusion, Culham Science Centre, Abingdon, Oxon., OX14 3EA
⁵⁾ Laboratory for Laser Energetics, 250 East River Rd., Rochester, NY 14623 USA

Abstract.  The sources of neutrals at the outer midplane of the plasma are discussed. We find that both the flux of neutrals escaping the divertor through leaks and ion recycling at main chamber surfaces appear to contribute. The ion flux to the walls is larger than the flux entering the divertor and comparable to recycling at the divertor plate. The cause of these high wall ion fluxes is an enhancement of cross-field particle transport which gives rise to substantial convective heat transport at higher densities. We have further explored main chamber recycling and impurity transport utilizing a novel divertor `bypass', which connects the outer divertor plenum to the main chamber. We find that leakage of neutrals (fuel and recycling impurities) from the divertor appears to be determined primarily by the conductance through the divertor structure, thus indicating that tight baffling would be desirable in a reactor for fuel and helium ash compression.

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