RF current condensation in the presence of turbulent enhanced transport

Turbulent Magnetic Reconnection in Two Dimensions

Two-dimensional numerical simulations of the effect of background turbulence on 2D resistive magnetic reconnection are presented. For sufficiently small values of the resistivity ($η$) and moderate values of the turbulent power ($ε$), the reconnection rate is found to have a much weaker dependence on $η$ than the Sweet-Parker scaling of $η^{1/2}$ and is even consistent with an $η-$independent value. For a given value of $η$, the dependence of the reconnection rate on the turbulent power exhibits a critical threshold in $ε$ above which the reconnection rate is significantly enhanced.

Saturation mechanism of the fluctuation dynamo in supersonic turbulent plasmas

Magnetic fields in several astrophysical objects are amplified and maintained by a dynamo mechanism, which is the conversion of the turbulent kinetic energy to magnetic energy. A dynamo that amplifies magnetic fields at scales $<$ the driving scale of turbulence is known as the fluctuation dynamo. We study the properties of the fluctuation dynamo in supersonic turbulent plasmas, which is of relevance to the ISM, structure formation, and lab experiments of laser-plasma turbulence. Using simulations, we explore the properties of the exponentially growing and saturated state of the fluctuation dy…

Proton Kinetic Effects and Turbulent Energy Cascade Rate in the Solar Wind

The first observed connection between kinetic instabilities driven by proton temperature anisotropy and estimated energy cascade rates in the turbulent solar wind is reported using measurements from the Wind spacecraft at 1 AU. We find enhanced cascade rates are concentrated along the boundaries of the ($β_{\parallel}$, $T_{\perp}/T_{\parallel}$)-plane, which includes regions theoretically unstable to the mirror and firehose instabilities. A strong correlation is observed between the estimated cascade rate and kinetic effects such as temperature anisotropy and plasma heating, resulting in prot…

On Turbulent Reconnection

We examine the dynamics of turbulent reconnection in 2D and 3D reduced MHD by calculating the effective dissipation due to coupling between small-scale fluctuations and large-scale magnetic fields. Sweet-Parker type balance relations are then used to calculate the global reconnection rate. Two approaches are employed -- quasi-linear closure and an eddy-damped fluid model. Results indicate that despite the presence of turbulence, the reconnection rate remains inversely proportional to $\sqrt{R_m}$, as in the Sweet-Parker analysis. In 2D, the global reconnection rate is shown to be enhanced over…

Experimental validation of a filament transport model in turbulent magnetized plasmas

In a wide variety of natural and laboratory magnetized plasmas, filaments appear as a result of interchange instability. These convective structures substantially enhance transport in the direction perpendicular to the magnetic field. According to filament models, their propagation may follow different regimes depending on the parallel closure of charge conservation. This is of paramount importance in magnetic fusion plasmas, as high collisionality in the scrape-off layer may trigger a regime transition leading to strongly enhanced perpendicular particle fluxes. This work reports for the first…

动力学螺旋度对磁场和标量场湍流扩散影响的理论

Theory of the kinetic helicity effect on turbulent diffusion of magnetic and scalar fields

本文采用路径积分方法研究有限相关时间、大雷诺数随机螺旋速度场，证明动力学螺旋度会减弱湍流磁扩散却增强被动标量扩散，并指出其源于速度相关时间的螺旋度依赖。

Enhanced Dissipation Rate of Magnetic Field in Striped Pulsar Winds by the Effect of Turbulence

In this letter we report on turbulent acceleration of the dissipation of magnetic field in the postshock re- gion of a Poynting flux-dominated flow, such as the Crab pulsar wind nebula. We have performed two- dimensional resistive relativistic magnetohydrodynamics simulations of subsonic turbulence driven by the Richtmyer-Meshkov instability at the shock fronts of the Poynting flux-dominated flows in pulsar winds. We find that turbulence stretches current sheets which substantially enhances the dissipation of magnetic field, and that most of the initial magnetic field energy is dissipated with…

Cross-helicity effects and turbulent transport in magnetohydrodynamic flow

In the presence of large-scale vortical motions and/or magnetic-field strains, the turbulent cross helicity (velocity--magnetic-field correlation in fluctuations) may contribute to the turbulent electromotive force and the Reynolds stress. These effects of cross helicity are considered to balance the primary effects of turbulence such as the turbulent magnetic diffusivity in magnetic-field evolution and the eddy viscosity in the momentum transport. The cross-helicity effects may suppress the enhanced transports due to turbulence. Physical interpretation of the effects is presented with special…

Turbulent energization of electron power law tails during magnetic reconnection

Earth's magnetotail is an excellent laboratory to study the interplay of reconnection and turbulence in determining electron energization. The process of formation of a power law tail during turbulent reconnection is a documented fact still in need of a comprehensive explanation. We conduct a massively parallel particle in cell 3D simulation and use enhanced statistical resolution of the high energy range of the particle velocities to study how reconnection creates the conditions for the tail to be formed. The process is not direct acceleration by the coherent, laminar, reconnection-generated …

螺旋度对湍流被动和主动标量扩散率的影响

Helicity effect on turbulent passive and active scalar diffusivities

本文通过数值模拟发现螺旋度会降低有效磁扩散率但增强被动标量扩散率，并证明速度场关联时间随动能螺旋度增加是解释该结果的关键。