A thermal transport coefficient for ohmic and ICRF plasmas inAlcator C-Mod

摘要

Summary form only given, as follows. The energy confinement inplasmas produced by Alcator C-Mod machine is markedly different fromthat observed by previous high field compact machines such as Alcator Aand C, FT, and more recently FTU. For ohmic plasmas at low and moderatedensities, the confinement times routinely exceed those expected fromthe so-called “neo-Alcator” scaling by a factor as high asthree. For both ohmic and ICRF heated plasmas, the energy confinementtime increases with the current and is approximately independent of thedensity. The similarity in the confinement between the ohmic and ICRFregimes opens the possibility that the thermal transport in AlcatorC-Mod may be described by one transport coefficient for both regimes. Weintroduce a modified form of a transport coefficient previously used todescribe ohmic plasmas in Alcator C-Mod. The coefficient is inspired byproperties of the so-called “ubiquitous” mode that can beexcited in the presence of a significant fraction of trapped electronsand also includes the constraint of profile consistency. A detailedseries of transport simulations are used to show that the proposedcoefficient can reproduce the observed temperature profiles, loopvoltage and energy confinement time for both ohmic and ICRF discharges.A total of nearly two dozen ohmic and ICRF Alcator C-Mod discharges havebeen fit over the range of parameter space available using thistransport coefficient