Conditions for the formation of nongyrotropic current sheets in slowly evolving plasmas

Abstract

This paper addresses the formation of nongyrotropic current sheets resulting from slow external driving. The medium is a collisionless plasma with one spatial dimension and a three-dimensional velocity space. The study is based on particle simulation and an analytical approach. Earlier results that apply to compression of an initial Harris sheet are generalized in several ways. In a first step a general sufficient criterion for the presence of extra ion and electron currents due to nongyrotropic plasma conditions is derived. Then cases with antisymmetric magnetic and electric fields are considered. After establishing consistency of the criterion with the earlier case, the usefulness of this concept is illustrated in detail by two further particle simulations. The results indicate that the formation of nongyrotropic current sheets is a ubiquitous phenomenon for plasmas with antisymmetric fields that have evolved slowly from initial gyrotropic states. A fourth case concerns a plasma with a unidirectional magnetic field. Consistent with the general criterion, the observed final state is fluidlike in that it is approximately gyrotropic. Momentum balance is shown to include a contribution that results from accumulation of an off-diagonal pressure tensor component during the evolution. Heat flux also plays an important role.

Forced reconnection in the near magnetotail: Onset and energy conversion in PIC and MHD simulations

“…The overall current concentration is similar in both PIC and MHD simulations; however, the internal structure differs. Similar substructures of the current sheet can also be found in PIC simulations of the slow compression of a one‐dimensional current sheet [ Schindler and Hesse , , ]. However, the current concentration and the increase in the peak current density by a factor of ~3.5 in the 2‐D case significantly exceed the values obtained in a 1‐D compression.…”

On the Fourier Contribution of Strong Current Sheets to the High‐Frequency Magnetic Power SpectralDensity of the Solar Wind

“…Finding #2 in Table points out that the spectral breakpoint is associated with the thicknesses of current sheets in the solar wind. As noted in Table , physical processes that act on the thicknesses of current sheets are important, such as plasma expansion and compression (Schindler & Hesse, , ), Bohm and gyro‐Bohm diffusion (Borovsky, ; Borovsky & Gary, ; Pecseli & Mikkelsen, ; Perkins et al, ; Vahala & Montgomery, ), eddy diffusion (Borovsky, ; Chen & Montgomery, ; Yoshizawa & Yokoi, ), Alfvén wave steepening (Tsurutani & Ho, ; Vasquez & Hollweg, ), current sheet instabilities (Birn et al, ; Daughton, ; Roytershteyn & Daughton, ), and reconnection (Faganello et al, ; Gosling & Phan, ; Yin & Winske, ).…”

“…Finding #3 in Table 2 points out that the profiles of solar wind current sheets determine the high-frequency magnetic spectra. As noted in Table 2, physical concepts that are important to the spatial profiles of current sheets are current sheet structuring (Gekelman et al, 2016;Ng et al, 2019;Schindler & Birn, 2002;Schindler & Hesse, 2008), plasma expansion and compression (Schindler & Hesse, 2008, 2010, Bohm and gyro-Bohm diffusion (Borovsky & Gary, 2009;Pecseli & Mikkelsen, 1985;Vahala & Montgomery, 1971), finite-gyroradii effects (Schindler & Hesse, 2010), ion versus electron current carriers (Aunai et al, 2013;Sasunov et al, 2016;Schindler & Birn, 2002), Alfvén wave nonlinear processes (Gomberoff, 2007;Tsurutani et al, 2002), plasma waves in current sheets (Huang et al, 2009;Malaspina et al, 2013;Verscharen & Marsch, 2011;Zelenyi et al, 2011), pressure balance Figure 13. The spectral slopes of the individual current sheets are plotted as a function of the Pearson linear correlation coefficient R corr between the logarithm of the power spectral density and the logarithm of the frequency in the frequency range where the spectral-slope fit is made.…”

Multipoint observations of dipolarization front formation by magnetotail reconnection

“…Thin current sheets with a sharp peak at the center and secondary peaks at the edges due to electron anisotropy were predicted in analytical models [ Zelenyi et al , 2004; Sitnov et al , 2006]. The triple‐peak current sheet profile has been also obtained in TCS expansion modeling [ Schindler and Hesse , 2010].…”