Modelling and consequences of drift effects in the edge plasma of Alcator C-Mod

We model the plasma edge of Alcator C-Mod with the B2-Eirene SOLPS5.0 code. The drifts, currents and neutral effects contribute to strong plasma rotation in the edge, as measured experimentally [B. LaBombard, S. Gangadhara, B. Lipschultz, C.S. Pitcher, J. Nucl. Mater. 313–316 (2003) 995; B. LaBombard, N. Smick, B. Lipschultz, J.L. Terry, J. Rice, these Proceedings; N. Smick, B. LaBombard, C.S. Pitcher, these Proceedings]. The plasma flow patterns are a complex superposition of several competing effects, including Pfirsch–Schlüter flows and currents, toroidal momentum generation and transport (with main chamber neutral recycling and drag playing an important role), as well as the E × B and diamagnetic drift flows. In the standard field direction the E × B flow in the core region adds to the toroidal plasma rotation, while in the reverse direction their respective contributions are roughly of the same order of magnitude but with opposite signs in the plasma core. However, in the edge, all terms can be of the same sign over most if not all of the radial extent of the SOL, leading to complex patterns and very strong flows.