PLEP-0001 – Purpose and Guidelines for PlasmaPy Enhancement Proposals

PlasmaPy Enhancement Proposals (PLEPs) are design documents that provide information to the PlasmaPy community, describe decision-making processes, or propose major changes or enhancements to the code. PLEPs are intended to be the primary mechanism for proposing major changes to the direction of PlasmaPy, collecting community feedback, and documenting the reasoning behind major decisions. This document describes the process for creating and deciding upon PLEPs

Non-equilibrium Ionization Modeling of Petschek-type Shocks in Reconnecting Current Sheets in Solar Eruptions

Non-equilibrium ionization (NEI) is essentially required for astrophysical plasma diagnostics once the plasma status departs from ionization equilibrium assumptions. In this work, we perform fast NEI calculations combined with magnetohydrodynamic (MHD) simulations and analyze the ionization properties of a Petschek-type magnetic reconnection current sheet during solar eruptions. Our simulation reveals Petschek-type slow-mode shocks in the classical Spitzer thermal conduction models and conduction flux-limitation situations. The results show that under-ionized features can be commonly found in shocked reconnection outflows and thermal halo regions outside the shocks. The departure from equilibrium ionization strongly depends on plasma density. In addition, this departure is sensitive to the observable target temperature: the high-temperature iron ions are strongly affected by NEI effects. The under-ionization also affects the synthetic SDO/AIA intensities, which indicates that the reconstructed hot reconnection current sheet structure may be significantly under-estimated either for temperature or apparent width. We also perform the MHD-NEI analysis on the reconnection current sheet in the classical solar flare geometry. Finally, we show the potential reversal between the under-ionized and over-ionized state at the lower tip of reconnection current sheets where the downward outflow collides with closed magnetic loops, which can strongly affect multiple SDO/AIA band ratios along the reconnection current sheet

The plasmoid instability during asymmetric inflow magnetic reconnection

High Lundquist number current sheets have recently been found to be unstable to the formation of plasmoids. Numerical simulations of this instability have usually assumed that the reconnecting magnetic fields are symmetric. We therefore present resistive MHD simulations of the plasmoid instability during asymmetric inflow reconnection. Asymmetry in the upstream magnetic fields modifies the scaling, onset, and dynamics of this instability. Plasmoids develop preferentially into the weak magnetic field region. Outflow jets from individual X-lines impact magnetic islands obliquely rather than directly as in the symmetric case. Consequently, momentum deposition into the magnetic islands from the outflow jets is less efficient and outward advection of the islands is somewhat slower. The islands also develop net vorticity. Finally, we discuss the implications these simulations may have on the dynamics of the plasmoid instability in three dimensions

The appearance, motion, and disappearance of three-dimensional magnetic null points

N.A.M. acknowledges support from NASA grants NNX11AB61G, NNX12AB25G, and NNX15AF43G; NASA contract NNM07AB07C; and NSF SHINE grants AGS-1156076 and AGS-1358342 to SAO. C.E.P. acknowledges support from the St Andrews 2013 STFC Consolidated grant.While theoretical models and simulations of magnetic reconnection often assume symmetry such that the magnetic null point when present is co-located with a flow stagnation point, the introduction of asymmetry typically leads to non-ideal flows across the null point. To understand this behavior, we present exact expressions for the motion of three-dimensional linear null points. The most general expression shows that linear null points move in the direction along which the magnetic field and its time derivative are antiparallel. Null point motion in resistive magnetohydrodynamics results from advection by the bulk plasma flow and resistive diffusion of the magnetic field, which allows non-ideal flows across topological boundaries. Null point motion is described intrinsically by parameters evaluated locally; however, global dynamics help set the local conditions at the null point. During a bifurcation of a degenerate null point into a null-null pair or the reverse, the instantaneous velocity of separation or convergence of the null-null pair will typically be infinite along the null space of the Jacobian matrix of the magnetic field, but with finite components in the directions orthogonal to the null space. Not all bifurcating null-null pairs are connected by a separator. Furthermore, except under special circumstances, there will not exist a straight line separator connecting a bifurcating null-null pair. The motion of separators cannot be described using solely local parameters because the identification of a particular field line as a separator may change as a result of non-ideal behavior elsewhere along the field line.Publisher PDFPeer reviewe