38 research outputs found
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Core Poloidal Rotation and Internal Trnasport Barrier Formation in TFTR
Impurity poloidal rotation velocities have been measured in the core of TFTR plasmas using a new spectroscopic diagnostic. Two types of transitions to enhanced confinement in reversed shear plasmas are examined. A bifurcation in carbon poloidal rotation is observed to occur before the transition to enhanced confinement for one of these types, while other measured plasmas parameters remain constant. A narrow radial region with reversed poloidal rotation and rotational shear is established 60-100 ms before the transition, and is associated with a large negative radial electric field
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Pressure-induced Breaking of Equilibrium Flux Surfaces in the W7AS Stellarator
Calculations are presented for two shots in the W7AS stellarator which differ only in the magnitude of the current in the divertor control coil, but have very different values of experimentally attainable β ( ≈ 2.7% versus ≈ 1.8%). Equilibrium calculations find that a region of chaotic magnetic field line trajectories fills approximately the outer 1/3 of the cross-section in each of these configurations. The field lines in the stochastic region are calculated to behave as if the flux surfaces are broken only locally near the outer midplane and are preserved elsewhere. The calculated magnetic field line diffusion coefficients in the stochastic regions for the two shots are consistent with the observed differences in the attainable β, and are also consistent with the differences in the reconstructed pressure profiles