Error field locked modes thresholds in rotating plasmas, anomalous braking and spin-up

Abstract

The mechanisms of nonlinear interaction of external helical fields with a rotating plasma are investigated analyzing the results of recent systematic experiments on the Joint European Torus (JET) [A. Gibson et al., Phys. Plasmas 5, 1839 (1998)] that widen the previous data base collected on Compass-D [T. C. Hender et al., Nucl. Fusion 32, 2091 (1992)], Doublet III-D [R. J. La Haye et al., Nucl. Fusion 32, 2119 (1992)] and JET. The empirical scaling laws governing the onset of “error field” locked modes are re-assessed and interpreted in terms of existing driven reconnection theories and with new models. In particular the important mechanisms of plasma rotation braking, and spin up, associated with error fields are analyzed in detail and interpreted.

Beta-limiting MHD Instabilities in Improved-performance NSTX Spherical Torus Plasmas

“…Resonant error fields resulting from loss of axisymmetry due to coil misalignments and other construction imperfections are well known to potentially lead to tokamak performance degradation [10][11][12][13]. This degradation typically occurs when the electromagnetic torque applied to resonant surfaces by the error field cannot be overcome by the intrinsic or externally driven torque of the plasma leading to error field penetration (locking) and loss of plasma rotation.…”

Role of singular layers in the plasma response to resonant magnetic perturbations

“…Efforts to improve the quantitative predictions of the theory have led to the realization that the non-resonant components of the field also affect the plasma rotation by giving rise to a neoclassical toroidal viscosity (NTV), which exerts a braking force proportional to the deviation of the rotation velocity from a value determined by neoclassical effects [49,50,51,52]. Bécoulet et al have examined the role of NTV forces in the context of ELM-suppression experiments [53].…”

Observation of Peak Neoclassical Toroidal Viscous Force in the DIII-D Tokamak

“…Experiments on DIII-D [8], JET [9], NSTX [10], and MAST [11] have all observed toroidal flow damping with the application of external NA fields in general agreement with the form given in (1). With the recent introduction of both co-and counter-I p neutral beam injection, the DIII-D tokamak is now able to access low toroidal rotation states and observe both toroidal flow damping and spin-up [12,13], to an offset value in qualitative agreement with Ω * defined in (5) below.…”