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P: Plasmaphysik

P 11: Magnetischer Einschluß 3

P 11.2: Talk

Tuesday, March 28, 2006, 11:45–12:00, 1004

Tokamak Edge Turbulence in a Self Consistent Equilibrium — •Bruce Scott — Max-Planck-IPP, Euratom Association, Garching, Germany

Tokamak edge turbulence is studied using three dimensional computations within low frequency gyrofluid and gyrokinetic models. The new feature is the simultaneous treatment of a time-dependently self consistent magnetic equilibrium. During major transition events such as large bursts the pressure gradient changes by as much as 50 percent, and the equilibrium follows, including flows and heat fluxes as well as the Pfirsch-Schlueter current. With a fixed heat source above a certain threshold, the turbulence/transport equilibrium is non-steady with most of the transport occurring in large bursts lasting for about one diamagnetic transit time and with a transport peak to trough ratio approaching one order of magnitude. Both results are commensurate with burst events observed in the edge regions of high performance tokamaks. The bursts are associated with the breakdown of the equilibrium, including destruction of the radial electric field shear layer, rather than the emergence of any new instability. The gyrofluid computations are carried for several edge-layer confinement times. The gyrokinetic ones are shorter but find similar behaviour.