Shielding of external magnetic perturbations by torque in rotating tokamak plasmas

• Published in: Physics of plasmas 2009-08, Vol.16 (8), p.082512-082512-7
• Main Authors: Park, Jong-Kyu, Boozer, Allen H., Menard, Jonathan E., Gerhardt, Stefan P., Sabbagh, Steve A.
• Format: Article
• Language: English
• ISSN: 1070-664X; 1089-7674
• DOI: 10.1063/1.3206668

The imposition of a nonaxisymmetric magnetic perturbation on a rotating tokamak plasma requires energy and toroidal torque. Fundamental electrodynamics implies that the torque is essentially limited and must be consistent with the external response of a plasma equilibrium f ⃗ = j ⃗ × B ⃗ . Here magnetic measurements on National Spherical Torus Experiment device are used to derive the energy and the torque, and these empirical evaluations are compared with theoretical calculations based on perturbed scalar pressure equilibria f ⃗ = ∇ ⃗ p coupled with the theory of nonambipolar transport. The measurement and the theory are consistent within acceptable uncertainties, but can be largely inconsistent when the torque is comparable to the energy. This is expected since the currents associated with the torque are ignored in scalar pressure equilibria, but these currents tend to shield the perturbation.