PFC / JA - 96 - 16 Experimental Investigation of Transport Phenomena in the Scrape - off Layer and Divertor

Transport physics in the divertor and scrape-off layer of Alcator C-Mod is investigated for a wide range of plasma conditions. Parallel (//) transport topics include: low-recycling, high-recycling, and detached regimes, thermoelectric currents, asymmetric heat fluxes driven by thermoelectric currents, and reversed divertor flows. Perpendicular (I) transport topics include: expected and measured scalings of I gradients with local conditions, estimated Xi profiles and scalings, divertor neutral retention effects, and L-mode/H-mode effects. Key results are: (i) classical // transport is obeyed with ion-neutral momentum coupling effects, (ii) I heat transport is proportional to local gradients, (iii) X± Te-0.6 n-0.6 L-0. 7 in L-mode, insensitive to toroidal field, (iv) X± is dependent on divertor neutral retention, (v) H-mode transport barrier effects partially extend inside the SOL, (vi) inside/outside divertor asymmetries may be caused by a thermoelectric instability, and (vii) reversed // flows depend on divertor asymmetries and their implicit ionization source imbalances. a) presently at University of California, San Diego, CA, USA. b) presently at McKinsey & Company, Inc., London, UK. c) presently at Tokyo Electron America, Beverly, MA, USA. d) presently at Applied Science and Technology, Inc., Woburn, MA, USA. e) presently at CPClare Corporation, Lexington, MA, USA. 1I B. LaBombard et al.: Invited Paper for 12th PSI Conference, San Raphael, May 1996.