Three-Dimensional Particle Acceleration in Electromagnetic Cylinder and Torus

Particle acceleration via Poynting vector with toroidal magnetic field is studied in 3D PIC simulation of electron-positron plasma. We choose two different initial magnetic field configurations to compare how the particle acceleration is affected by the expansion of electromagnetic wave. In the cylindrical case, the electromagnetic field strength decays as (ct)⁻², and particles are accelerated in the radial direction as well as the axial direction. Rayleigh-Taylor instability is also observed at the center of the cylinder. In the torus case, the field strength decays as (ct)⁻³, making the acceleration less efficient. Particles accelerated in the axial direction by E × B force creates strong charge separation.     

A new low-frequency electrostatic mode in a nonuniform electron-positron plasma

The existence of a novel low-frequency electrostatic mode, which is due to the gravitational acceleration in a nonuniform electron-positron plasma, is pointed out. At large amplitudes, the unstable modes self-organize to form dipolar vortices.     

The example of effective plasma acceleration in a magnetosphere

The problem of effective transform of Poynting flux energy into the kinetic energy of relativistic plasma outflow in a magnetosphere is considered. In this article we present an example of such acceleration. In order to perform it, we use the approach of ideal axisymmetric magnetohydrodynamics (MHD). For highly magnetized plasma outflow we show that a linear growth of Lorentz factor with a cylindrical distance from the rotational axis is a general result for any field configuration in the sub-magnetosonic flow. In the far region the full magnetohydrodynamics problem for one-dimensional flow is considered. It turns out that the effective plasma outflow acceleration is possible in the paraboloidal magnetic field. It is shown that such an acceleration is due to the drift of charged particles in the crossed electric and magnetic field. The clear explanation of the absence of acceleration in the monopole magnetic field if given.      

Simulating Poynting Flux Acceleration in the Laboratory with Colliding Laser Pulses

We review recent PIC simulation results which show that double-sided irradiation of a thin over-dense plasma slab with ultra-intense laser pulses from both sides can lead to sustained comoving Poynting flux acceleration of electrons to energies much higher than the conventional ponderomotive limit. The result is a robust power-law electron momentum spectrum similar to astrophysical sources. We discuss future ultra-intense laser experiments that may be used to simulate astrophysical particle acceleration.     

The termination shock in a striped pulsar wind

The origin of radio emission from plerions is considered. Recent observations suggest that radio-emitting electrons are presently accelerated rather than having been injected at early stages of the plerion evolution. The observed flat spectra without a low-frequency cut-off imply an acceleration mechanism that raises the average particle energy by orders of magnitude but leaves most of the particles at an energy of less than approximately a few hundred MeV. It is suggested that annihilation of the alternating magnetic field at the pulsar wind termination shock provides the necessary mechanism. Toroidal stripes of opposite magnetic polarity are formed in the wind emanating from an obliquely rotating pulsar magnetosphere (the striped wind). At the termination shock, the flow compresses and the magnetic field annihilates by driven reconnection. Jump conditions are obtained for the shock in a striped wind. It is shown that the post-shock magnetohydrodynamic parameters of the flow are the same as if the energy of the alternating field had already been converted into plasma energy upstream of the shock. Therefore, the available estimates of the ratio of the Poynting flux to the matter energy flux, σ, should be attributed not to the total upstream Poynting flux but only to that associated with the average magnetic field. A simple model for the particle acceleration in the shocked striped wind is presented.     

Relativistic large-scale jets and minimum power requirements

The recent discovery, by the Chandra satellite, that jets of blazars are strong X-ray emitters at large scales     , lends support to the hypothesis that emitting plasma is still moving at highly relativistic speeds on these scales. In this case in fact the emission via inverse Compton scattering off cosmic background photons is enhanced and the resulting predicted X-ray spectrum accounts well for the otherwise puzzling observations. Here we point out another reason to favour relativistic large-scale jets, based on a minimum power argument: by estimating the Poynting flux and bulk kinetic powers corresponding to, at least, the relativistic particles and magnetic field responsible for the emission, one can derive the value of the bulk Lorentz factor for which the total power is minimized. It is found that both the inner and extended parts of the jet of PKS     satisfy such a condition.     

Propagation of microwaves in pulsar magnetospheres

We discuss the dispersion relation of linearly-polarized waves, propagating along a strong background magnetic field embedded in an electron-positron plasma. The results are then applied to the study of the propagation conditions of coherent curvature radio radiation inside neutron stars magnetospheres, as produced by electric discharges following current pulsar models.     

The Cretaceous/Paleogene (K‐Pg) boundary at the J Anomaly Ridge,Newfoundland (IODP Expedition 342, Hole U1403B)

We present results of an in‐situ geochemical study using laser‐ablation inductively coupled plasma–mass spectrometry (LA‐ICP‐MS) analyses along a ~4.3 cm long section across the K‐Pg event bed, drilled during IODP Expedition 342 at J Anomaly Ridge south of St. John's, Newfoundland. This section comprises the Maastrichtian with a sharp boundary to the graded, between 1.5 and 1.8 cm thick ejecta layer with totally altered impact glass spherules, which in turn is topped by Danian sediments. The porous and clayey material required elaborate preparation in order to yield reliable data. The ejecta bed shows a highly variable depletion in rare earth elements that even results in strongly subchondritic concentrations. The Ce/Ce* varies strongly (0.81–34), Ni/Cr ranges from 0.38 to 2.79. The maximum platinum group elements (PGE) concentrations are located in one LA‐spot exactly at the basis of the ejecta layer; they amount (in μg g^?1) to 0.35 (Rh), 1.64 (Pd), 2.79 (Pt), and 0.86 (Au). The Nb/Ta ratio increases in the Ma from ~10 to 35.9 toward the ejecta horizon, which itself has higher Nb, Ta, Zr, and Hf concentrations than the background sedimentation, combined with low Nb/Ta (~5–10), and low Zr/Hf (~20–30). The overall result is that alteration processes changed totally the original geochemical characteristics of this K‐Pg spherule bed. To explain the exorbitant element mobility at distances of hundreds of μm, we discuss a combination of mostly reducing redox processes and interaction with organic compounds. This study demonstrates the high potential of in‐situ analyses with high spatial resolution at complex geological materials. Moreover, our results indicate that some caution is necessary in determining the projectile type in impactites via PGE ratios.     

Electron-positron pairs production in the pulsar magnetosphere

The case of an aligned rotator magnetosphere is considered. Provided the ions ejection from the neutron stellar surface is absent, the pulsar magnetosphere consists of two polar electron caps. The upper parts of the caps are unstable. Electrons precipitate from these parts, fall onto the star and are accelerated to Lorentz-factor 10⁶–10⁷. Electrons radiate -quanta in the direction of the star. These -quanta are converted into electron-positron pairs. The region of size, about 10 stellar radii, around the star appears to be filled with electron-positron plasma. The inflow of electron-positron plasma interacts with the electron gas of the polar cap. For this reason longitudinal plasma vibrations arise, and bunched outflows of electron-positron plasma appear.     

Generation of electromagnetic waves in the electron-positron plasma in the vicinity of a pulsar

The problem of the efficiency of the ion-synchrotron maser proposed by Hoshino and Arons is analyzed in a linear approximation. A hot, relativistic, electron-positron plasma penetrated by a relativistic ion beam is considered. At the front of the magnetosonic shock wave an electromagnetic wave is generated, which should be damped on positrons of the plasma. This should, in turn, result in synchrotron emission from energetic positrons in the high-frequency range, far above the natural frequencies of the plasma. It is shown that one must allow simultaneously for the conditions of resonance at a high harmonic of the ion-cyclotron frequency and at the fundamental of the electron-cyclotron frequency. Natural transverse waves are generated in the process, but within the framework of the linear theory there is no positron acceleration due to the kinetic energy of ions. Translated from Astrofizika, Vol. 43, No. 3, pp. 389-396, July–September, 2000.     

Numerical construction of magnetosphere with relativistic two-fluid plasma flows

We present a numerical model in which a cold pair plasma is ejected with relativistic speed through a polar cap region and flows almost radially outside the light cylinder. Stationary axisymmetric structures of electromagnetic fields and plasma flows are self-consistently calculated. In our model, motions of positively and negatively charged particles are assumed to be determined by electromagnetic forces and inertial terms, without pair creation and annihilation or radiation loss. The global electromagnetic fields are calculated by the Maxwell's equations for the plasma density and velocity, without using ideal magnetohydrodynamic condition. Numerical result demonstrates the acceleration and deceleration of plasma due to parallel component of the electric fields. Numerical model is successfully constructed for weak magnetic fields or highly relativistic fluid velocity, i.e. kinetic energy dominated outflow. It is found that appropriate choices of boundary conditions and plasma injection model at the polar cap should be explored in order to extend present method to more realistic pulsar magnetosphere, in which the Poynting flux is dominated.     

Nonlinear Drift-Alfvén Waves in Relativistically Hot Nonuniform Electron-Positron Plasmas

The magnetic viscosity tensor is derived for a magnetized relativistic collisionless plasma with temperature gradients. By means of this tensor we deduce the nonlinear equations for drift–Alfvén waves in a relativistic electron-positron low plasma with density and temperature gradients. It is shown that our new equations have solutions in the form of dipolar vortices. The present results should be relevant to a number of astrophysical objects with strong electron-positron pair production, e.g. in pulsars as well as in accretion disks and jets.     

Formation of Expanding Envelopes in Wolf-Rayet Stars

Some features of the envelopes of WR stars have not yet been explained in terms of the standard stellar wind. One of these features is the presence of gas condensations (clumps) in the envelopes. In this paper the possible reasons for clump formation are examined along with their role in the structure of envelopes. Clumps can be formed in the transitional zone between a star and its envelope because of instabilities in the gas. This zone lies much deeper than the "optical radus" of the star, so it cannot be observed. A clump expands as it moves under the action of radiation pressure from the star and its density decreases at the same time. The clump mixes with the surrounding gas if its mass is low. Large clumps can reach the visible region of the envelope.     

Experimental Studies of Magnetically Driven Plasma Jets

We present experimental results on the formation of supersonic, radiatively cooled jets driven by pressure due to the toroidal magnetic field generated by the 1.5 MA, 250 ns current from the MAGPIE generator. The morphology of the jet produced in the experiments is relevant to astrophysical jet scenarios in which a jet on the axis of a magnetic cavity is collimated by a toroidal magnetic field as it expands into the ambient medium. The jets in the experiments have similar Mach number, plasma beta and cooling parameter to those in protostellar jets. Additionally the Reynolds, magnetic Reynolds and Peclet numbers are much larger than unity, allowing the experiments to be scaled to astrophysical flows. The experimental configuration allows for the generation of episodic magnetic cavities, suggesting that periodic fluctuations near the source may be responsible for some of the variability observed in astrophysical jets. Preliminary measurements of kinetic, magnetic and Poynting energy of the jets in our experiments are presented and discussed, together with estimates of their temperature and trapped toroidal magnetic field.     

Effects of plasma rotation on alfvén solitons in pulsar magnetospheres

Nonlinear Alfvén wave in a hot rotating and strongly magnetized electron-positron plasma is considered. Using relativistic two fluid equations, the dispersion relation for Alfvén wave in the rotating plasma is obtained. Large amplitude Alfvén solitons are found to exist in the rotating pulsar plasma. Rotational effects on solitons are discussed.     

Nonlinear coupling between electromagnetic fields in a strongly magnetized electron-positron plasma

The nonlinear coupling between electromagnetic fields in a strongly magnetized electron-positron plasma is considered. We point out that compressional magnetic field perturbations are excited by the rotational part of the nonlinear current, and derive a new nonlinear system of equations that is basic for studies of modulational instabilities and coherent nonlinear structures in magnetized electron-positron plasmas.     

On the production of hard X-rays in solar flares

The problem of producing the hard X-ray burst at the onset of solar flares may be thought of in terms of the problem of producing the non-thermal electrons which emit the X-rays via bremsstrahlung. Electron acceleration to relativistic energies without similar ion acceleration is difficult to achieve, even in an ad hoc theoretical model. Yet from global energetic considerations, it is not feasible to accelerate the electrons as a minor constituent of the total energetic particle population. Therefore, it is necessary to invoke a more sophisticated process for the electron acceleration. In this paper we describe a mechanism for achieving this via an initial acceleration of a neutralized ion beam. When such a beam impacts the chromosphere, the electrons start to scatter while the ions continue downwards, rapidly setting up an electric field which is either cancelled by the inflow of background chromospheric electrons or results in the runaway acceleration of beam electrons. In the former case the result is simply heating, whereas in the latter case much of the ion kinetic energy is transferred into electron kinetic energy. The final electron energy may be similar to the typical energy of the ions. The electrons that are accelerated are those in the neutral beam that experience an electric field greater than the critical Dreicer field. Thus there will be a low-energy cut-off to the electron spectrum which overcomes the well-known energetics problem at low energies with certain other spectral forms.     

Comparison Between Halo cme Expansion Speeds Observed on the Sun,the Related Shock Transit Speeds to Earth and Corresponding Ejecta Speeds at 1 au

We have compared characteristics of 38 halo coronal mass ejections observed on the Sun by the Large Angle and Spectrometric Coronagraph onboard SOHO with their corresponding counterparts observed near Earth by the magnetic field and plasma instruments onboard the ACE, WIND and SOHO satellites, in the period from January 1997 to April 2001. We only have selected events that have some associated interplanetary ejecta structure at 1 AU and we have compared the lateral expansion speeds of these halo CMEs and the corresponding ejecta speeds near Earth. We found that there is a high correlation between these two speeds. The results are very similar to the study done by Lindsay et al. (1999) using observations made by Solwind and SMM coronagraphs, and Helios-1 and PVO plasma and interplanetary field data from the period of 1979 to 1988. Also, we reviewed the relation between the CME-related shock transit speed to Earth and the ejecta speeds near Earth. This kind of relation is very important to estimate ejecta speeds of events for which no interplanetary observations are available.     

Petrography and geochemistry of ejecta from the Sudbury impact event

Ejecta from the Connors Creek site in Michigan (500 km from the Sudbury Igneous Complex [SIC]), the Pine River site in western Ontario (650 km from the SIC), and the Coleraine site in Minnesota (980 km from the SIC) were petrographically and geochemically analyzed. Connors Creek was found to have approximately 2 m of ejecta, including shocked quartz, melt droplets, and accretionary lapilli; Pine River has similar deposits about 1 m in thickness, although with smaller lapilli; Coleraine contains only impact spherules in a 20 cm‐thick layer (impact spherules being similar to microkrystites or microtektites). The ejecta transition from chaotic deposits of massively bedded impactoclastic material with locally derived detritus at Connors Creek to a deposit with apparently very little detrital material that is primarily composed of melt droplets at Pine River to a deposit that is almost entirely composed of melt spherules at Coleraine. The major and trace element compositions of the ejecta confirm the previously observed similarity of the ejecta deposits to the Onaping Formation in the SIC. Platinum‐group element (PGE) concentrations from each of the sites were also measured, revealing significantly elevated PGE contents in the spherule samples compared with background values. PGE abundances in samples from the Pine River site can be reproduced by addition of approximately 0.2 wt% CI chondrite to the background composition of the underlying sediments in the core. PGE interelement ratios indicate that the Sudbury impact event was probably caused by a chondritic impactor.     

The mechanism of magnetospheric substorm and the MHD waves of the solar wind

A mechanism of the Earth's magnetospheric substorm is proposed. It is suggested that the MHD waves may propagate across the magnetopause from the magnetosheath into the magnetotail and will be dissipated in the plasma sheet, heating the plasma and accelerating the particles. When the solar wind parameters change, the Poynting flux of the waves transferred from the magnetosheath into the tail, may be greater than 10¹⁸ erg s^?1. The heated plasma and accelerated particles in the plasma sheet will be injected into the inner magnetosphere, and this may explain the process of the ring current formation and auroral substorm.The Alfvén wave can only propagate along the magnetic force line into the magnetosphere in the open magnetosphere, but the magnetosonic wave can propagate in both the open and closed magnetosphere. When the IMF turns southward, the configuration of the magnetosphere will change from a nearly closed model into some kind of open one. The energy flux of Alfvén waves is generally larger than that of the magnetosonic wave. This implies that it is easy to produce substorms when the interplanetary magnetic field (IMF) has a large southward component, but the substorm can also be produced even if the IMF is directed northward.