556 research outputs found
A note on the Weibel instability and thermal fluctuations
The thermal fluctuation level of the Weibel instability is recalculated. It
is shown that the divergence of the fluctuations at long wavelengths, i.e. the
Weibel infrared catastrophe, never occurs. At large wavelengths the thermal
fluctuation level is terminated by the presence of even the smallest available
stable thermal anisotropy. Weibel fields penetrate only one skin depth into the
plasma. When excited inside, they cause layers of antiparallel fields of skin
depth width and vortices which may be subject to reconnection.Comment: 4 pages, 2 figures, accepted by Ann Geophy
Collisionless reconnection: Mechanism of self-ignition in thin current sheets
The spontaneous onset of magnetic reconnection in thin collisionless current
sheets is shown to result from a thermal-anisotropy driven magnetic
Weibel-mode, generating seed-magnetic field {\sf X}-points in the centre of the
current layer.Comment: 8 pages, 6 figures, prepared for Annales Geophysica
Collisionless reconnection: The sub-microscale mechanism of magnetic field line interaction
Magnetic field lines are quantum objects carrying one quantum
of magnetic flux and have finite radius . Here
we argue that they possess a very specific dynamical interaction. Parallel
field lines reject each other. When confined to a certain area they form
two-dimensional lattices of hexagonal structure. We estimate the filling factor
of such an area. Antiparallel field lines, on the other hand, attract each
other. We identify the physical mechanism as being due to the action of the
gauge potential field which we determine quantum mechanically for two parallel
and two antiparallel field lines. The distortion of the quantum electrodynamic
vacuum causes a cloud of virtual pairs. We calculate the virtual pair
production rate from quantum electrodynamics and estimate the virtual pair
cloud density, pair current and Lorentz force density acting on the field lines
via the pair cloud. These properties of field line dynamics become important in
collisionless reconnection, consistently explaining why and how reconnection
can spontaneously set on in the field-free centre of a current sheet below the
electron-inertial scale.Comment: 13 journal pages, 6 figures, submitted to Ann. Geophy
Plasma wave mediated electron pairing effects
Pairing of particles, in particular electrons, in high temperature plasma is
generally not expected to occur. Here we investigate, based on earlier work,
the possibility for electron pairing mediated in the presence of various kinds
of plasma waves. We confirm the possibility for pairing in ion- and
electron-acoustic waves, pointing out the importance of the former and the
expected consequences. While electron-acoustic waves probably do not play any
role, ion-acoustic waves may cause formation of heavy electron compounds. Lower
hybrid waves also mediate pairing but under different conditions. Buneman modes
which evolve from strong currents may cause pairing among trapped electrons
constituting a heavy electron component that populates electron holes. All
pairing processes are found to generate cold pair populations. They provide a
mechanism of electron cooling which can be interpreted as kind of classical
condensation, in some cases possibly accompanied by formation of current
filaments, weak soft-X-ray emission and superfluidity which might affect
reconnection physics.Comment: Ready for submission, Journal not yet specified. 10 pages, 2 figure
Superdiffusion revisited in view of collisionless reconnection
The concept of diffusion in collisionless space plasmas like those near the
magnetopause and in the geomagnetic tail during reconnection is reexamined
making use of the division of particle orbits into waiting orbits and
break-outs into ballistic motion lying at the bottom, for instance, of Lévy
flights. The rms average displacement in this case increases with time,
describing superdiffusion, though faster than classical, is still a weak
process, being however strong enough to support fast reconnection. Referring
to two kinds of numerical particle-in-cell simulations we determine the
anomalous diffusion coefficient, the anomalous collision frequency on which
the diffusion process is based, and construct a relation between the
diffusion coefficients and the resistive scale. The anomalous collision
frequency from electron pseudo-viscosity in reconnection turns out to be of
the order of the lower-hybrid frequency with the latter providing a lower
limit, thus making similar assumptions physically meaningful. Tentative
though not completely justified use of the κ distribution yields
κ ≈ 6 in the reconnection diffusion region and, for the anomalous
diffusion coefficient, the order of several times Bohm diffusivity
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