Energy Of Fast Particles Research Articles

Magnetic reconnection on the Sun: ESPD Senior Prize Lecture

Magnetic reconnection is a fundamental process for changing the magnetic topology and converting magnetic energy into other forms on the Sun, such as heat, flow energy and fast particle energy. In two dimensions it is fairly well understood, although some aspects still need to be developed. In three dimensions, it behaves very differently and a substantial body of theory and numerical experiment has now been built up, including reconnection at null points, separators and quasi-separators.Some aspects of solar flares can be understood with 2D reconnection models, but other aspects such as the shapes of flare ribbons, the acceleration of particles and the creation of twist in erupting flux ropes need a 3D understanding. A paradigm shift in our understanding of coronal heating by reconnection has been stimulated by dramatic new observations of photospheric flux cancellation from SUNRISE and from SST together with the realisation that it may well be driving nanoflare heating events and possibly campfires.

Condensation of plasmon-polaritons in dispersive carbon nanotubes assisted by a fast charge

Capturing the energy of fast charged particles by nanostructures opens up access to new affordable and environmentally friendly solutions in the field of energy. However, the condition for this (Cherenkov emission) in dispersionless media is attainable only for very fast particles. We propose to use for this purpose the excitation of surface plasmon polaritons in a three-dimensional (3D) array of dispersive carbon nanotubes (CNTs) assisted by a fast charge. In such a dispersive system, the radiation occurs even if the particle speed is less than the speed of light in the material (E.Fermi). The inclusion of an array of CNTs leads to that such a composite system becomes spatially inhomogeneous, which significantly modifies the field dynamics. Our numerical 3D modeling shows that the properties of the field created in such a composite drastically depend on the value of the plasma frequency ω p of carbon nanotubes. Local short-wave fields of plasmon-polaritons arise here already in the subcritical region. At large ω p , the reconnection of local fields leads to transition in a delocalized state (plasmon-polaritons condensate), when collective field oscillations occupy macroscopicaly large region of the CNT and the inverse partisipation ratio attains a minimum. This effect can find interesting applications in modern ‘laboratory-on-a-chip’ technologies for capturing and accumulation of the pure energy of fast particles by plasmon-polaritons of carbon nanostructures.

Three-dimensional magnetic reconnection in astrophysical plasmas

Magnetic reconnection is a fundamental process in laboratory, magnetospheric, solar and astrophysical plasmas, whereby magnetic energy is converted into heat, bulk kinetic energy and fast particle energy. Its nature in two dimensions is much better understood than that in three dimensions, where its character is completely different and has many diverse aspects that are currently being explored. Here, we focus on the magnetohydrodynamics of three-dimensional reconnection in the plasma environment of the Solar System, especially solar flares. The theory of reconnection at null points, separators and quasi-separators is described, together with accounts of numerical simulations and observations of these three types of reconnection. The distinction between separator and quasi-separator reconnection is a theoretical one that is unimportant for the observations of energy release. A new paradigm for solar flares, in which three-dimensional reconnection plays a central role, is proposed.

Magnetic reconnection in terms of catastrophe theory

Magnetic field line reconnection (magnetic reconnection) is a phenomenon that occurs in space and laboratory plasma. Magnetic reconnection allows both the change the magnetic topology and the conversion of the magnetic energy into energy of fast particles. The critical point (critical line or plane in higher dimensional cases) of the magnetic field play an important role in process of magnetic reconnection, as in its neighborhood occurs a change of its topology of a magnetic field and redistribution of magnetic field energy. A lot of literature is devoted to the analytical and numerical investigation of the reconnection process. The main result of these investigations as the result of magnetic reconnection the current sheet is formed and the magnetic topology is changed. While the studies of magnetic reconnection in 2D and 3D configurations have a led to several important results, many questions remain open, including the behavior of a magnetic field in the neighborhood of a critical point of high order. The magnetic reconnection problem is closely related to the problem of the structural stability of vector fields. Since the magnetic field topology changes during both spontaneous and induced magnetic reconnection, it is natural to expect that the magnetic field should evolve from a structurally unstable into a structurally stable configuration. Note that, in this case, the phenomenon under analysis is more complicated since, during magnetic reconnection in a highly conducting plasma, we deal with the non-linear interaction between two vector fields: the magnetic field and the field of the plasma velocities. The aim of our article is to consider the process of magnetic reconnection and transformation of the magnetic topology from the viewpoint of catastrophe theory. Bifurcations in similar configurations (2D magnetic configuration with null high order point) with varying parameters were thoroughly discussed in a monograph by Poston and Stewart.

Axisymmetric global Alfvén eigenmodes within the ellipticity-induced frequency gap in the Joint European Torus

Alfvén eigenmodes (AEs) with toroidal mode number n = 0 (i.e., axisymmetric) have been observed in the ellipticity-induced frequency range in the Joint European Torus. The axisymmetric modes are of interest because they can be used to diagnose fast particle energy distributions at the mode location. The modes were identified as global Alfvén eigenmodes (GAEs), with the ellipticity of the plasma cross-section preventing strong continuum damping of the modes. The MHD codes CSCAS, MISHKA, and AEGIS were used to compute the n = 0 Alfvén continuum, eigenmode structure, and continuum damping. For zero ellipticity, a single mode exists at a frequency below the Alfvén continuum branch. This mode has two dominant poloidal harmonics with poloidal mode numbers m = ±1 that have the same polarity; therefore, it is an even mode. For finite ellipticity, the continuum branch splits into two branches and the single GAE splits into two modes. An even mode exists below the minimum of the top continuum branch, and the frequency of this mode coincides with the experimentally observed AE frequency. The other mode is found below the lower continuum branch with opposite signs between the two poloidal harmonics (an odd mode structure). This mode was not excited in our experiment. Analytical theory for the n = 0 GAE in an elliptical cylinder shows the n = 0 Alfvén continuum agrees with the numerical modelling.

Our dynamic sun: 2017 Hannes Alfvén Medal lecture at the EGU

Abstract. This lecture summarises how our understanding of many aspects of the Sun has been revolutionised over the past few years by new observations and models. Much of the dynamic behaviour of the Sun is driven by the magnetic field since, in the outer atmosphere, it represents the largest source of energy by far. The interior of the Sun possesses a strong shear layer at the base of the convection zone, where sunspot magnetic fields are generated. A small-scale dynamo may also be operating near the surface of the Sun, generating magnetic fields that thread the lowest layer of the solar atmosphere, the turbulent photosphere. Above the photosphere lies the highly dynamic fine-scale chromosphere, and beyond that is the rare corona at high temperatures exceeding 1 million degrees K. Possible magnetic mechanisms for heating the corona and driving the solar wind (two intriguing and unsolved puzzles) are described. Other puzzles include the structure of giant flux ropes, known as prominences, which have complex fine structure. Occasionally, they erupt and produce huge ejections of mass and magnetic fields (coronal mass ejections), which can disrupt the space environment of the Earth. When such eruptions originate in active regions around sunspots, they are also associated with solar flares, in which magnetic energy is converted to kinetic energy, heat and fast-particle energy. A new theory will be presented for the origin of the twist that is observed in erupting prominences and for the nature of reconnection in the rise phase of an eruptive flare or coronal mass ejection.

A hierarchy of electromagnetic gyrokinetic and fluid hybrid models for the simulation of global modes

The goal of magnetic confinement fusion research is to produce an economically viable power reactor. This will require operation at finite plasma β, where for instance fast particle transport by Alfvén eigenmodes may become important. The density and energy of fast particles originating from heating and fusion will also be higher. Low frequency Alfvénic modes can be destabilised by fast particles, with velocities comparable to the Alfvén velocity, resulting in significant reduction of fast particle confinement. To properly predict and manipulate this behaviour in current and future fusion devices, the numerical simulation of fast particle interaction with Alfvén modes is necessary. Since these simulations are computationally demanding, it is desirable to use the simplest model capable of simulating a given phenomenon. Comparing a case with different physical models also permits the isolation of physics effects responsible for certain phenomena. In this paper we present a hierarchy of such numerical models and investigate their ranges of validity.

Large ELM-like events triggered by core MHD in JET advanced tokamak plasmas: impact on plasmas profiles, plasma-facing components and heating systems

Large and infrequent collapse events have been observed in high βN advanced tokamak (AT) plasmas in JET. Although they have features similar to large ELMs, they were triggered by core MHD. They caused a considerable loss of the plasma thermal and fast particle energy (∼10% of the total stored energy), but the heat load in the divertor due to these collapse events was small as a fraction of the plasma energy loss compared with regular type-I ELMs. Instead, significant heating of the main chamber wall was observed. A large, toroidally asymmetric, increase in the neutral gas pressure outside the plasma was observed after such events, which caused arcs in the lower hybrid (LH) and ion cyclotron (IC) heating systems and increased reionization in the neutral beam (NB) injectors. The collapses resulted in a reduction in the electron and ion temperatures and toroidal rotation of the whole plasma, a rise in Zeff; and a sufficiently large increase in the peripheral electron density to completely black-out the ECE emission from the plasma core. These features have been modelled to gain an understanding of the plasma behaviour associated with these collapse events and the implication for the operation of AT plasma scenarios with high additional heating power will be discussed.

Gyrokinetic calculations of diffusive and convective transport of α particles with a slowing-down distribution function

Quasilinear gyrokinetic calculations of the transport of fast α particles with a slowing-down equilibrium distribution function in the trace limit are presented. Diffusive and convective contributions to the total flux are separated and their dependence on the ratio of the fast particle energy to the background plasma temperature is investigated. The results are compared with those obtained in the case an equivalent Maxwellian distribution function is assumed for the fast particles. On the basis of the gyrokinetic results, simple models for α particle transport are proposed for transport modeling purposes.

Fast-particle energy loss to a quantum well

Electron energy loss spectroscopy (EELS) to a single GaAs–AlGaAs quantum well is considered for a charged particle moving parallel to the two-dimensional electron gas (2DEG) within the framework of the random-phase approximation (RPA). For the single-quantum well structure, a modulation-doped GaAs–AlGaAs heterostructure is considered. The Schrödinger–Poisson solver is used to obtain the electron eigenstates. We present theoretical results for the electron energy loss to intersubband and intrasubband plasmons and particle–hole modes using the inverse dielectric function (IDF) formalism.

Cyclotron resonance maser as a solar flare trigger

We propose a new mechanism of solar flaring, which is based on explosive phenomena in magnetic traps in the presence of a two-component plasma composed of fast electrons with anisotropic velocity distribution and a dense cold background plasma with high ionization. It is assumed that such a plasma is generated in a coronal magnetic trap in a preflare stage. This system, which is essentially a cyclotron resonance maser, becomes unstable under certain conditions and gives rise to an explosive cyclotron instability, which develops at first in a very small local area and is accompanied by intense heating of the background plasma and release of fast electrons at the trap ends. The energy of fast particles is collected from the entire volume of the magnetic trap and is localized in the form of heat in the explosion area from which thermal and shock waves are propagated. The model makes it possible to explain the main solar flare effects.

Commensurability oscillations in fast particle energy loss to a density modulated 2DEG in a magnetic field

We examine fast particle energy loss as a probe of the properties of a density modulated 2DEG in a normal magnetic field. In the high velocity limit, the local plasmon spectrum makes two separate contributions to energy loss for both the cases in which the particle velocity is parallel and perpendicular to the planar 2DEG. The inter-Landau band plasmon makes a distinct contribution to energy loss through excitation of the hybrid 2D magnetoplasmon. The other local plasmon, associated with the spread of a Landau level into a miniband by application of the periodic potential associated with the density modulation contributes to energy loss with features corresponding to Shubnikov-de Haas oscillations jointly with an amplitude envelope exhibiting oscillations associated with the commensurability of the modulation period and the cyclotron radius at the Fermi energy.

Fast-particle energy loss to a layered electron gas.

The energy loss of a fast-charged-particle probe of an array of parallel two-dimensional (2D) electron-gas layers is calculated. The two-dimensional electron-gas (2D EG) layers are equally spaced and are used to model modulation-doped semiconductor superlattices such as GaAs-(${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$)As in the electric quantum limit where only the lowest subband is occupied. The 2D EG layers of the model system are embedded in a slab with background dielectric constant \ensuremath{\epsilon}, with vacuum on one side and a material with background dielectric constant ${\ensuremath{\epsilon}}_{0}$ on the other. The dielectric materials screen the Coulomb interaction between electrons which are confined to the 2D planes. The fast-particle motion is taken to be parallel to the 2D plasma layers which are assumed to be at zero temperature. The electronic response dynamics are described in the random-phase approximation. The energy loss is determined as a function of the distance of the fast particle from the surface of the superlattice and its velocity.

Fast-particle energy loss in the vicinity of a two-dimensional plasma.

This paper presents an analysis of the energy loss of a fast-charged-particle probe of a two-dimensional (2D) collisionless solid-state plasma. The fast-particle motion is taken to be parallel to the 2D plasma sheet, and the plasma is taken to be in a degenerate state (zero temperature). The 2D plasma response dynamics are described in the random-phase approximation (RPA), and our calculation is a 2D analogue of the well-known Nozi\`eres-Pines energy-loss calculation, but with the particle's trajectory at a fixed distance H from the plane of the 2D plasma sheet. Our calculation includes a determination of the part of the fast particle's energy loss which can be ascribed to the excitation of electron-hole pairs in the 2D plasma, as well as the part which can be ascribed to 2D plasmons (of all wave numbers). We determine the energy loss as a function of the distance of the fast particle from the 2D plasma plane, and its velocity.

790. Influence of impurities on the energy of fast particles in a coaxial source: V P Goncharenko and V M Mishchenko, Zh Tekh Fiz, 38 (2), Feb 1968, 264–267 ( in Russian).

790. Influence of impurities on the energy of fast particles in a coaxial source: V P Goncharenko and V M Mishchenko, Zh Tekh Fiz, 38 (2), Feb 1968, 264–267 ( in Russian).

Origin of Ultrarelativistic Cosmic Ray Particles

A mechanism is proposed to explain how cosmic rays and fast electrons in non-thermal radio sources originate. The theory develops from Fermi's suggestion that charged particles gain energy through successive encounters with moving magnetic fields. Considerations of the geometry of cosmic magnetic fields and the state of motion of the plasma indicate how magnetic energy may be converted into kinetic energy of fast particles and how such particles may be later released.

Direct transformation of magnetic-field energy into energy of fast particles

There are two distinct but as it seems strongly connected problems. The first is the surprisingly rapid dissipation of magnetic fields which is observed in the Sun's atmosphere and must be supposed for some other objects as well. The second problem is the acceleration of fast particles in magnetized cosmical plasma.