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(TH3/7) Theory for Angular Momentum Generation and the Problem of Poloidal Rotation

B. Coppi, G. Penn, L. E. Sugiyama

Massachusetts Institute of Technology, Cambridge MA, United States of America

Abstract.  Results of the investigation of two basic problems involving the rotation of magnetically confined plasmas are presented. In the toroidal direction, significant plasma rotation has been produced in plasmas subject to ion cyclotron RF heating, in the absence of any evident direct angular momentum source. The theoretical model proposes the excitation of two classes of intrinsic magnetosonic whistler-like modes. The first, ``contained'' modes, has toroidal momentum in the same direction as that of the plasma current and is radially localized in the outer region of the plasma column, r > 0.4a. The other class is nonlocal and convects radially outwards, carrying the angular momentum in the counter-current direction to particles near the edge of the plasma column that are then scattered out of the plasma. Thus, rotation of the central part of the plasma column can be induced, with a velocity radial profile that is consistent with the anomalous transport of angular momentum resulting from the additional excitation of velocity-gradient-driven modes. The question of poloidal rotation and the evolution of poloidal flows in a torus is also examined. Results from the numerical simulation of MHD and two-fluid plasmas shows that compressional and other effects are important in the plasma response to rotation and provide an effective mechanism for damping poloidal flows in a torus on relatively fast time scales. The two-fluid response to rotation can be different than in MHD, due to differences in the symmetries of the equations, but they experience similar break-up of the poloidal rotation.

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IAEA 2001