Resonance enhanced turbulent transport

Enhanced Doppler Effect in the Upper Hybrid Resonance Microwave Backscattering Experiment

Observations of enhanced Doppler frequency shift effect of the highly localized microwave backscattering in the upper hybrid resonance are reported. The experiment is performed at FT-2 tokamak, where a steerable focusing antenna set, allowing off equatorial plane plasma extraordinary wave probing from high magnetic field side, was installed. A separate line less than 1.5 MHz wide and shifted by up to 2 MHz is routinely observed in the backscattering spectrum under condition of accessible upper hybrid resonance. The enhanced frequency shift is explained by the growth of poloidal wave number of …

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…

Turbulent transport of MeV range cyclotron heated minorities as compared to alpha particles

We study the turbulent transport of an ion cyclotron resonance heated (ICRH), MeV range minority ion species in tokamak plasmas. Such highly energetic minorities, which can be produced in the three ion minority heating scheme [Ye. O. Kazakov et al. (2015) Nucl. Fusion 55, 032001], have been proposed to be used to experimentally study the confinement properties of fast ions without the generation of fusion alphas. We compare the turbulent transport properties of ICRH ions with that of fusion born alpha particles. Our theoretical predictions indicate that care must be taken when conclusions are …

Enhanced Attenuation Arising from Lattice Resonances in a Plasma Photonic Crystal

We describe the experimental verification of lattice resonances in two-dimensional photonic crystals constructed from an array of gaseous plasma columns. Enhancements are seen in the extinction of normal incidence transverse electric electromagnetic waves when the localized surface plasmon modes of the plasma columns are shifted into the vicinity of the photonic crystal Bragg resonances. Simulations and experiments are in reasonable agreement and confirm the appearance of a Fano-like profile with deep and broad extinction bands. The broadening of the spectra as surface plasmon modes come into …

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…

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。

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…

在具有超光速相速度的直接激光加速过程中通过高阶共振增强能量增益

Enhanced energy gain through higher-order resonances during direct laser acceleration with superluminal phase velocity

本文研究超光速相速度下的直接激光加速，揭示其产生的非单调频率比可在宽能区内维持高阶共振匹配，使高阶共振取代基频电子感应加速器共振成为增强电子能量增益的主导机制。

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…

Resonance-broadened transit time damping of particles in MHD turbulence

As a fundamental astrophysical process, the scattering of particles by turbulent magnetic fields has its physical foundation laid by the magnetohydrodynamic (MHD) turbulence theory. In the framework of the modern theory of MHD turbulence, we derive a generalized broadened resonance function by taking into account both the magnetic fluctuations and nonlinear decorrelation of turbulent magnetic fields arising in MHD turbulence, and we specify the energy range of particles for the dominance of different broadening mechanisms. The broadened resonance allows for scattering of particles beyond the e…

Electron acceleration by turbulent plasmoid reconnection

In space and astrophysical plasmas, like in planetary magnetospheres, as that of Mercury,energetic electrons are often found near current sheets (CSs), which hints at electron acceleration by magnetic reconnection. Unfortunately, electron acceleration by reconnection is not well understood, yet. In particular, acceleration by turbulent plasmoid reconnection. We have investigated electron acceleration by turbulent plasmoid reconnection, described by MHD simulations, via test particle calculations. In order to avoid resolving all relevant turbulence scales down to the dissipation scales, a mean-…