The gyrokinetic (GK) electron and fully kinetic ion (GeFi) simulation model of Lin et al. [Plasmas Phys. Controlled Fusion 53, 054013 (2011)] has been thoroughly benchmarked and validated for a two-dimensional (2D) Harris current sheet with a finite guide field. First, a gyrokinetic eigenmode theory for the collisionless tearing mode in the small Larmor radius limit is presented. The linear eigenmode structure and growth rate of the tearing mode obtained from the GeFi simulation are benchmarked against those from the GK eigenmode analysis in the limit of L≫ρi>ρe, where L is the current sheet half-width, ρi is ion Larmor radius, and ρe is electron Larmor radius. Second, to valid the GeFi model, both the linear and nonlinear tearing instabilities obtained from the GeFi simulations are compared with the Darwin particle-in-cell (PIC) simulation. The validation of the GeFi model for laboratory and space plasmas is also discussed. Meanwhile, the GeFi simulation is carried out to investigate both the linear and nonlinear tearing instabilities for cases with a broad range of L and guide magnetic field BG. It is found that in a wide current sheet with L > 4.5ρeK, the nonlinear saturation level of the island half-width is ws ≃ 3ρeK, where ρeK = ρeB0/Bx0, B0 is the strength of the asymptotic magnetic field, and Bx0 is the antiparallel field. On the other hand, in a thin current sheet with L < 2.5ρeK, ws ≃ 2.2 L. In addition, a high frequency electrostatic drift mode is found to coexist with the tearing mode.

No abstract

The normal mode equation for coupled drift and Alfv6n waves in a finite-B nonuniform plasma with a sheared magnetic field is solved, in the slab geometry, to investigate the instability of slow Alfv6n waves. It is shown, that, besides having an appreciable growth rate, the instability also produces microscopic "tearing" of the rational surfaces which has important implications for anomalous transport.

This work was supported by U. S, IQ1ergy I&sea.ch and Depelopaent ~i s t. r a t i~(~ Contract W-76-002-3073, lkproductios1, tcansla-tia~, publicaticm, use a d disposal, in whole or in part, by or far the Ihlited states GoParnrment is permitted, DISCLAIMER This report was prepared as an account of work sponsored by an agency of the United States Government.