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(TH/2-6) Plasma and Momentum Transport Processes in the Vicinity of a Magnetic Island in a Tokamak

K.C. Shaing¹⁾, C.C. Hegna¹⁾, J.D. Callen¹⁾, W.A. Houlberg^2)
 
1) Engineering Physics Department, University of Wisconsin, Madison, WI, USA
²⁾ Fusion Energy Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA

Abstract.  In the vicinity of a magnetic island, the toroidal symmetry of the equilibrium magnetic field strength B is broken in tokamaks due to the finite width of the island. The magnitude of the broken symmetry is of the order of the square root of the perturbed magnetic field strength. This leads to enhanced plasma transport in the vicinity of the island. The ratio of the symmetry-breaking-induced heat flux to that of the banana regime flux can be significantly greater than unity in low collisionality regimes. The magnitude of the island-induced transport fluxes can be comparable to that of the anomalous transport fluxes. It is also shown that these symmetry-breaking-induced fluxes are driven by the toroidal pressure tensor. The toroidal momentum can, thus, be affected. Island-induced fluxes can change the toroidal rotation. Finally, the radial electric field in the vicinity of the island can be determined from the momentum balance. We find the momentum equation is a nonlinear function of the radial electric field. It can have bifurcated solutions. Thus, in the vicinity of a magnetic island, plasma confinement can have high(H)-mode like phenomenon.

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