The role of polarization current in magnetic island evolution

Abstract

The polarization current plays an important role in the evolution of magnetic islands with a width comparable to the characteristic ion orbit width. Understanding the evolution of such small magnetic islands is important for two reasons: (1) to investigate the threshold mechanisms for growth of large-scale islands (e.g., neoclassical tearing modes), and (2) to describe the drive mechanisms for small-scale magnetic turbulence and consequent transport. This article presents a two-fluid, cold ion, collisional analysis of the role of the polarization current in magnetic island evolution in slab geometry. It focuses on the role played by the conjunction of parallel electron dynamics and perpendicular transport (particle diffusion and viscosity) in determining the island rotation frequency and the distribution of the polarization current within the island.

Multiscale interaction of a tearing mode with drift wave turbulence: A minimal self-consistent model

“…Finally, we note that previous studies of ͑ * ͒ modified tearing modes have invoked outgoing wave boundary conditions for similar reasons. 32 Like other familiar cases of outgoing wave boundary conditions, the damping does not appear explicitly in the theory, as outgoing wave boundary conditions tacitly presume a sink for the outgoing wave. As shown in Appendix A, this outgoing wave energy condition implies that A / B is pure imaginary, so the dispersion relation takes the form…”

Effect of externally applied resonant magnetic perturbations on resistive tearing modes

“…When the island width is not too large, however, a variety of stabilizing or destabilizing mechanisms are involved, such as the ion polarization current [11][12][13][14][15][16] and the plasma viscosity [14,17]. The classical tearing mode stability in low β plasmas has been investigated in [18].…”

Two-fluid magnetic island dynamics in slab geometry. I. Isolated islands

“…(62)]. 16 It follows, from our result for the island phase-velocity, that the polarization term is stabilizing when the anomalous perpendicular ion viscosity significantly exceeds the anomalous perpendicular electron viscosity [see Fig. 1, left panel].…”

“…Magnetic island physics is less completely understood within the context of two-fluid, drift-MHD theory, [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] which is far more relevant to present-day magnetic confinement devices than single-fluid theory. In two-fluid theory, the island is generally embedded within ion and electron fluids which flow at different velocities.…”