82 research outputs found
The Suppression of Radiation Reaction and Laser Field Depletion in Laser-Electron beam interaction
The effects of radiation reaction (RR) have been studied extensively by using
the ultraintense laser interacts with the counter-propagating relativistic
electron. At the laser intensity at the order of W/cm, the
effects of RR are significant in a few laser period for a relativistic
electron. However, the laser at such intensity is tightly focused and the laser
energy is usually assumed to be fixed. Then, the signal of RR and energy
conservation cannot be guaranteed. To assess the effects of RR in a tightly
focused laser pulse and the evolution of the laser energy, we simulate this
interaction with a beam of electrons by means of Particle-in-Cell (PIC)
method. We observed that the effects of RR are suppressed due to the
ponderomotive force and accompanied by a non-negligible amount of laser field
energy reduction. This is due to the ponderomotive force that prevents the
electrons from approaching the center of the laser pulse and leads to the
interaction at weaker field region. At the same time, the laser energy is
absorbed through ponderomotive acceleration. Thus, the kinetic energy of the
electron beam has to be carefully selected such that the effects of RR become
obvious.Comment: 6 pages, 3 figure
Pair Plasma Dominance in the Parsec-Scale Relativistic Jet of 3C345
We investigate whether a pc-scale jet of 3C345 is dominated by a normal
plasma or an electron-positron plasma. We present a general condition that a
jet component becomes optically thick for synchrotron self-absorption, by
extending the method originally developed by Reynolds et al. The general
condition gives a lower limit of the electron number density, with the aid of
the surface brightness condition, which enables us to compute the magnetic
field density. Comparing the lower limit with another independent constraint
for the electron density that is deduced from the kinetic luminosity, we can
distinguish the matter content. We apply the procedure to the five components
of 3C345 (C2, C3, C4, C5, and C7) of which angular diameters and radio fluxes
at the peak frequencies were obtainable from literature. Evaluating the
representative values of Doppler beaming factors by their equipartition values,
we find that all the five components are likely dominated by an
electron-positron plasma. The conclusion does not depend on the lower cutoff
energy of the power-law distribution of radiating particles.Comment: 17 page
New Insights into Dissipation in the Electron Layer During Magnetic Reconnection
Detailed comparisons are reported between laboratory observations of
electron-scale dissipation layers near a reconnecting X-line and direct
two-dimensional full-particle simulations. Many experimental features of the
electron layers, such as insensitivity to the ion mass, are reproduced by the
simulations; the layer thickness, however, is about 3-5 times larger than the
predictions. Consequently, the leading candidate 2D mechanism based on
collisionless electron nongyrotropic pressure is insufficient to explain the
observed reconnection rates. These results suggest that, in addition to the
residual collisions, 3D effects play an important role in electron-scale
dissipation during fast reconnection.Comment: 17 pages, 4 figure
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