Investigation of tearing instability using GeFi particle simulation model

Abstract

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.

Numerical comparison between a gyrofluid and gyrokinetic model investigating collisionless magnetic reconnection

“…An analysis of the eigenvalues and the eigenmode structure is given here for both the linearised gyrofluid and the gyrokinetic equations. The gyrofluid equations (14)(15)(16)(17)(18)(19)(20), and the gy-rokinetic equations (5-9), are linearised using the ansatz δΦ (x, y, t) = e i(ky y−ωt) Φ(x) and δA (x, y, t) = e i(ky y−ωt) Ã(x) for the perturbed quantities, additionally assuming a long-wavelength approximation for the quasineutrality equation, Eq. ( 9).…”

“…The saturated island half width w and oscillation frequency ω B in the deeply nonlinear phase are the two most relevant observables. Up to now, in the literature there are only a few extended simulation results of these quantities in homogeneous plasmas [14,15,18].…”

“…Simulations of the collisionless tearing mode with gyrokinetic electrons and fully kinetic ions were performed in Ref. [18] and compared with the asymptotic matching theory of Ref. [16], and with a gyrokinetic eigenmode theory in a small but finite Larmor radius limit.…”

A closed high-frequency Vlasov–Maxwell simulation model in toroidal geometry

“…Instead of directly solving the perpendicular Ampère's law, GeFi applies the force balance equation to calculate the perturbed parallel magnetic field δB , which is then used to compute the perturbed vector potential δA through Ampère's law. A two dimensional kinetic code based on this model was then developed in slab geometry to study the physics of Harris sheet [40] and tearing instability [41], which was followed by the simulations of propagation property [42] and Landau damping [43] of LHW in uniform plasmas.…”

Benchmark Simulations of Gyro-Kinetic Electron and Fully-Kinetic Ion Model for Lower Hybrid Waves in Linear Region

“…In this way, relatively larger time steps and spatial grids can be adopted, and the computation cost can be significantly improved over that of the traditional full-particle codes. Furthermore, the code can be used to study relatively longer evolution processes while the realistic ion to electron mass ratio remains unchanged [22,23] . Currently, GeFi has already been used to study the Landau damping process of LHWs in uniform plasmas [24] .…”