| 1. |
- Dieckmann, Mark E, 1969-, et al.
(author)
-
Electron surfing acceleration by mildly relativistic beams : wave magnetic field effects
- 2008
-
In: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 10:Januar, s. 013029-1-13029-2
-
Journal article (peer-reviewed)abstract
- Electron surfing acceleration (ESA) is based on the trapping of electrons by a wave and the transport of the trapped electrons across a perpendicular magnetic field. ESA can accelerate electrons to relativistic speeds and it may thus produce hot electrons in plasmas supporting fast ion beams, like close to astrophysical shocks. One-dimensional (1D) particle-in-cell (PIC) simulations have demonstrated that trapped electron structures (phase space holes) are stabilized by relativistic phase speeds of the waves, by which ESA can accelerate electrons to ultrarelativistic speeds. The 2(1/2)D electromagnetic and relativistic PIC simulations performed in the present paper model proton beam driven instabilities in the presence of a magnetic field perpendicular to the simulation plane. This configuration represents the partially electromagnetic mixed modes and the filamentation modes, in addition to the Buneman waves. The waves are found to become predominantly electromagnetic and nonplanar for beam speeds that would result in stable trapped electron structures. The relativistic boost of ESA reported previously is cancelled by this effect. For proton beam speeds of 0.6 and 0.8c, the electrons reach only million electron volt energies. The system with the slower beam is followed sufficiently long in time to reveal the development of a secondary filamentation instability. The instability forms a channel in the simulation domain that is void of any magnetic field. Proton beams may thereby cross perpendicular magnetic fields for distances beyond their gyroradius.
|
|
| 2. |
- Dieckmann, Mark E, 1969-, et al.
(author)
-
The formation of a relativistic partially electromagnetic planar plasma shock
- 2008
-
In: Astrophysical Journal. - : American Astronomical Society. - 0004-637X .- 1538-4357. ; 675:1, s. 586-595
-
Journal article (peer-reviewed)abstract
- Relativistically colliding plasma is modeled by particle-in-cell simulations in one and two spatial dimensions, with an ion-to-electron mass ratio of 400 and a temperature of 100 keV. The energy of an initial quasi-parallel magnetic field is 1% of the plasma kinetic energy. Energy dissipation by a growing wave pulse of mixed polarity, probably an oblique whistler wave, and different densities of the colliding plasma slabs result in the formation of an energetic electromagnetic structure within milliseconds. The structure, which develops for an initial collision speed of 0.9c, accelerates electrons to Lorentz factors of several hundred. A downstream region forms, separating the forward and reverse shocks. In this region, the plasma approaches an energy equipartition between electrons, ions, and the magnetic field. The electron energy spectrum resembles a power law at high energies, with an exponent close to −2.7, or . The magnetic field reflects upstream ions, which form a beam and drag the electrons along to preserve the plasma quasineutrality. The forward and reverse shocks are asymmetric due to the unequal slab densities. The forward shock may be representative for the internal shocks of gamma-ray bursts.
|
|
| 3. |
- Marklund, Mattias, et al.
(author)
-
Magnetosonic solitons in a dusty plasma slab
- 2008
-
In: Journal of Plasma Physics. - Cambridge : Cambridge University Press. - 0022-3778 .- 1469-7807. ; 74:5, s. 601-605
-
Journal article (peer-reviewed)abstract
- The existence of magnetosonic solitons in dusty plasmas is investigated. The nonlinear magnetohydrodynamic equations for a warm dusty magnetoplasma are thus derived. A solution of the nonlinear equations is presented. It is shown that, owing to the presence of dust, static structures are allowed. This is in sharp contrast to the formation of the so-called shocklets in usual magnetoplasmas. A comparatively small number of dust particles can thus drastically alter the behavior of the nonlinear structures in magnetized plasmas.
|
|
