arXiv subjects

R. Schopper

Publications and source records attributed to R. Schopper.

3 recordsLinked to original sources

arXiv2003

Particle acceleration in three-dimensional tearing configurations

In three-dimensional electromagnetic configurations that result from unstable resistive tearing modes particles can efficiently be accelerated to relativistic energies. To prove this resistive magnetohydrodynamic simulations are used as input configurations for successive test particle simulations. The simulations show the capability of three-dimensional non-linearly evolved tearing modes to accelerate particles perpendicular to the plane of the reconnecting magnetic field components. The simulations differ considerably from analytical approaches by involving a realistic three-dimensional electric field with a non-homogenous component parallel to the current direction. The resulting particle spectra exhibit strong pitch-angle anisotropies. Typically, about 5-8 % of an initially Maxwellian distribution is accelerated to the maximum energy levels given by the macroscopic generalized electric potential structure. Results are shown for both, non-relativistic particle acceleration that is of interest, e.g., in the context of auroral arcs and solar flares, and relativistic particle energization that is relevant, e.g., in the context of active galactic nuclei.

astro-ph↗

arXiv2002

The Free Electron Maser in Pulsar Magnetospheres

We present the numerical simulations of coherent inverse Compton scattering (CICS) in a highly magnetized plasma process by means of a full three dimensional particle in cell code (PIC), which is mass and energy conservative. We used the parameters of a pulsar magnetosphere where CICS is one of the most promising models for the generation of the observed highly coherent radio emission. First we show details of the onset and time evolution of strong Langmuir turbulence driven by a relativistic electron beam penetrating a strongly magnetized background plasma. The Langmuir turbulence acts as self-generated wiggler fields which bunch the beam electrons thereby inducing strong coherent emission of the bunches at frequency gamma^2 times the plasma frequency. The emitted power is about 10 GW in a few nanoseconds. This radiation is interpreted in terms of inverse Compton scattering on nonlinear density fluctuations. CICS is the longitudinal version of a laboratory free electron laser and is applicable in strongly magnetized plasmas like pulsars.

astro-ph↗

arXiv1998

Magnetic Reconnection and Particle Acceleration in Active Galactic Nuclei

Magnetic field-aligned electric fields are characteristic features of magnetic reconnection processes operating in externally agitated magnetized plasmas. An especially interesting environment for such a process are the coronae of accretion disks in active galactic nuclei (AGN). There, Keplerian shear flows perturb the quite strong disk magnetic field leading to intense current sheets. It was previously shown that given field strengths of 200 G in a shear flow, reconnection driven magnetic field aligned electric fields can accelerate electrons up to Lorentz factors of about 2000 in those objects thus providing us with a possible solution of the injection (pre-acceleration) problem. However, whereas in the framework of magnetohydrodynamics the formation of the field-aligned electric fields can be described consistently, the question has to be addressed whether the charged particles can really be accelerated up to the maximum energy supplied by the field-aligned electric potentials, since the accelerated particles undergo energy losses either by synchrotron or inverse Compton mechanisms. We present relativistic particle simulations starting from electric and magnetic fields obtained from magnetohydrodynamic simulations of magnetic reconnection in an idealized AGN configuration including nonthermal radiative losses. The numerical results prove that the relativistic electrons can be effectively accelerated even in the presence of an intense radiation bath. Energies from 50 MeV up to 40 GeV can be reached easily, depending on the energy density of the photon bath.

astro-ph↗