Divertor tokamak operation at high densities on ASDEX Upgrade
Densities achievable in ASDEX Upgrade discharges are restricted by a disruptive limit in the L-mode caused by an edge-power imbalance which is linking divertor detachment, Marfe formation and the separatrix density. In H-mode an upper density limit is found which represents a non-disruptive H-L back transition. Close to the Greenwald limit this H-L transition cannot be avoided at any power flux across the separatrix and confinement degrades even before the back transition. The H-mode operational window is determined by local edge-barrier parameters and their gradients. The boundaries are represented by the L-H transition-temperature threshold, the ideal ballooning edge-pressure gradient limit, the upper temperature limit for type-III edge-localized modes (ELM) and an upper H-mode barrier density limitation. Despite the limited edge densities the Greenwald density could be surpassed by a factor of three with pellet refuelling from the low magnetic-field side. In contrast to the temperature-profile resilience density profiles can be changed both by deep refuelling and intrinsic transport improvements connected with density peaking, which offers the combination of high confinement and high density operation. The possible alliance with radiation cooling, divertor detachment and divertor compatible type-III ELMs could solve the power exhaust problem.
Bibliographic Reference: Article: Plasma Physics and Controlled Fusion, Vol. 39 (1997), pp. B19-B38
Record Number: 199810323 / Last updated on: 1998-03-09
Original language: en
Available languages: en