Solar radio observations provide a unique diagnostic of the outer solar atmosphere. However, inhomogeneous turbulent corona strongly affects propagation emitted waves, so decoupling intrinsic properties emitting source from effects radio-wave has long been major challenge in physics. Here we report quantitative spatial and frequency characterization burst fine structures observed with LOw Frequency Array (LOFAR), an instrument high time resolution that also permits imaging at scales much...

This paper presents the results of three-dimensional fluid global simulations electrostatic ion turbulence in tokamaks with reversed magnetic shear. It is found that a transport barrier appears at location shear reversal. due to rarefaction resonant surfaces this region. For same reason, more pronounced when minimum safety factor simple rational number. The broadened by velocity effects. also large-scale events hardly cross barrier. Finally, significant amount toroidal rotation generated...

Radial convection of isolated filamentary structures due to interchange motions in magnetized plasmas is investigated. Following a basic discussion vorticity generation, ballooning, and the role sheaths, two-field model studied by means numerical simulations on biperiodic domain perpendicular magnetic field. It demonstrated that blob-like plasma structure develops dipolar electrostatic potential fields, resulting rapid radial acceleration formation steep front trailing wake. While dynamical...

The energy released in solar flares derives from a reconfiguration of magnetic fields to lower state, and is manifested several forms, including bulk kinetic the coronal mass ejection, acceleration electrons ions, enhanced thermal that ultimately radiated away across electromagnetic spectrum optical x rays. Using an unprecedented set coordinated observations, suite instruments, we here report on hitherto largely overlooked component-the associated with small-scale turbulent motions. We show...

Recent observations from {\em RHESSI} have revealed that the number of non-thermal electrons in coronal part a flaring loop can exceed required to explain hard X-ray-emitting footpoints same loop. Such sources cannot, therefore, be interpreted on basis standard collisional transport model, which stream along while losing their energy through collisions with ambient plasma; additional physical processes, either trap or scatter energetic electrons, are required. Motivated by this and other...

Large-scale radial advection of isolated structures in nonuniformly magnetized plasmas is investigated. The underlying mechanism considered due to the nonlinear evolution interchange motions, without any presumption plasma sheaths. Theoretical arguments supported by numerical simulations reveal an inertial scaling for velocity ideal limit. This increases as square root structure size relative length scale magnetic field. magnitude velocity, well dynamical structures, compares favorably with...

Twisted coronal loops should be ubiquitous in the solar corona. magnetic fields contain excess energy, which can released during reconnection, causing flares. The aim of this work is to investigate and particle acceleration transport kink-unstable twisted loops, with a focus on effects resistivity, loop geometry atmospheric stratification. Another perform forward-modelling bremsstrahlung emission determine structure hard X-ray sources. We use combination magnetohydrodynamic (MHD)...

Driven by recent RHESSI observations of confined loop-top hard X-ray sources in solar flares, we consider stochastic acceleration electrons the presence Coulomb collisions. If electron escape from region can be neglected, distribution function is determined a balance between diffusive and Such scenario admits stationary solution for that takes form kappa distribution. We show evolution toward this involves "wave front" propagating forwards velocity space, so higher energy are accelerated...

In this paper we show the self-consistent evolution of an isolated density perturbation in models tokamak scrape-off layer turbulence. Our purpose is to explain possible mechanisms responsible for radial propagation perturbations observed layer. Results both two-dimensional numerical simulations and one-dimensional quasilinear modeling propagative events are presented, shown be consistent with many experimental observations. The role sheath dissipation front turbulent mixing also addressed.

Plasma turbulence is thought to be associated with various physical processes involved in solar flares, including magnetic reconnection, particle acceleration and transport. Using Ramaty High Energy Solar Spectroscopic Imager ({\it RHESSI}) observations the X-ray visibility analysis, we determine spatial spectral distributions of energetic electrons for a flare (GOES M3.7 class, April 14, 2002 23$:$55 UT), which was previously found consistent reconnection scenario. It demonstrated that...

Extending previous studies of nonthermal electron transport in solar flares, which include the effects collisional energy diffusion and thermalization fast electrons, we present an analytic method to infer more accurate estimates accelerated spectrum flares from observations hard X-ray spectrum. Unlike for standard cold-target model, spatial characteristics flaring region, especially necessity consider a finite volume hot plasma source, need be taken into account order correctly obtain...

Observations with RHESSI have enabled the detailed study of structure dense hard X-ray coronal sources in solar flares. The variation source extent electron energy has been discussed context streaming non-thermal particles a one-dimensional cold target model and results used to constrain both physical of, density within, acceleration region. Here, we extend this investigation more physically realistic transport that takes into account finite temperature ambient plasma, initial pitch angle...

ABSTRACT The transport of the energy contained in electrons, both thermal and suprathermal, solar flares plays a key role our understanding many aspects flare phenomenon, from spatial distribution hard X-ray emission to global energetics. Motivated by recent RHESSI observations that point existence mechanism confines electrons coronal parts loops more effectively than Coulomb collisions, we here consider impact pitch-angle scattering off turbulent magnetic fluctuations on parallel flaring...

High-energy charged particles are produced during solar flares. These may be accelerated by the strong electric fields associated with magnetic reconnection process which is source of energy release in A simple model random acceleration due to fragmented considered for case a turbulent reconnecting plasma fluctuating field highly localized and its magnitude distributed according power laws. The statistical properties expressed terms fractional diffusion equation velocity space, whose...

We establish a classification scheme for stochastic acceleration models involving low-frequency plasma turbulence in strongly magnetized plasma. This takes into account both the properties of accelerating electromagnetic field, and nature transport charged particles region. group processes as either resonant, non-resonant, or resonant-broadened, depending on whether particle motion is free-streaming along magnetic diffusive, combination two. Stochastic by moving mirrors adiabatic...

{This work aims to investigate the spectral structure of parallel electric field generated by strong anisotropic and balanced Alfvenic turbulence in relation with problem electron acceleration from thermal population solar flare plasma conditions.} {We consider fluctuations presence a background magnetic field. Exploiting this anisotropy, set reduced equations governing non-linear, two-fluid dynamics is derived. The low-$\beta$ limit model used follow turbulent cascade energy resulting...

The acceleration of charged particles in magnetized plasmas is considered during turbulent multi-island magnetic reconnection. particle model constructed for an ensemble islands which produce adiabatic compression the particles. takes into account statistical fluctuations rate experienced by their transport region. evolution distribution function described as a simultaneous first and second-order Fermi process. While efficiency first-order process controlled average compression, second order...

Context. High-energy electrons accelerated during solar flares are abundant in the corona and interplanetary space. Commonly, number energy of non-thermal at Sun is estimated through hard X-ray (HXR) spectral observations (e.g. RHESSI) a single-particle collisional approximation.

We investigate the impact of turbulent suppression parallel heat conduction on cooling post-flare coronal loops. Depending value mean free path $\lambda_T$ associated with scattering process, we identify four main scenarios. The overall temperature evolution, from an initial in excess $10^7$~K, is modeled each case, highlighting evolution dominant mechanism throughout process. Comparison observed times allows to be constrained, and interestingly this range corresponds situations where...

Large scale transport events are studied using two different 3-D simulation codes related to resistive ballooning and ion temperature gradient turbulence. The turbulence is driven by a constant incoming flux. In the case of simulations, underlying structures found be radially elongated on low field side distorted magnetic shear in parallel direction (streamers). non-linear character these emphasized. Bursty investigated presence zonal flows internal barriers generated either strong flow or...

In this contribution some recent investigations of two-dimensional thermal convection relevant to ordinary fluids as well magnetized plasmas are reviewed. An introductory discussion is given the physical mechanism for baroclinic vorticity generation and convective motions in stratified fluids, emphasizing its relation interchange non-uniformly plasmas. This followed by a review theories onset quasi-linear saturation driven-dissipative systems. Non-linear numerical simulations which result...

Abstract The heat flux in a plasma is determined by the degree of anisotropy particle distribution function, which turn driven gradients ambient density and temperature. When mean free path at thermal speed substantially smaller than scale length associated with temperature variation, simply depends on local value gradient. However, when are comparable, conduction becomes non-local character: magnitude now overall profile generally locally value. In presence angular scattering turbulence,...

Using the "enthalpy-based thermal evolution of loops" (EBTEL) model, we investigate hydrodynamics plasma in a flaring coronal loop which heat conduction is limited by turbulent scattering electrons that transport flux. The EBTEL equations are solved analytically each two (conduction-dominated and radiation-dominated) cooling phases. Comparison results with typical observed times solar flares shows mean free path λT lies range corresponding to regime classical (collision-dominated) plays at...