1,375 research outputs found
Particle Acceleration and Plasma Dynamics during Magnetic Reconnection in the Magnetically-dominated Regime
Magnetic reconnection is thought to be the driver for many explosive
phenomena in the universe. The energy release and particle acceleration during
reconnection have been proposed as a mechanism for producing high-energy
emissions and cosmic rays. We carry out two- and three-dimensional kinetic
simulations to investigate relativistic magnetic reconnection and the
associated particle acceleration. The simulations focus on electron-positron
plasmas starting with a magnetically dominated, force-free current sheet
(). For this limit, we demonstrate
that relativistic reconnection is highly efficient at accelerating particles
through a first-order Fermi process accomplished by the curvature drift of
particles along the electric field induced by the relativistic flows. This
mechanism gives rise to the formation of hard power-law spectra and approaches for sufficiently large and
system size. Eventually most of the available magnetic free energy is converted
into nonthermal particle kinetic energy. An analytic model is presented to
explain the key results and predict a general condition for the formation of
power-law distributions. The development of reconnection in these regimes leads
to relativistic inflow and outflow speeds and enhanced reconnection rates
relative to non-relativistic regimes. In the three-dimensional simulation, the
interplay between secondary kink and tearing instabilities leads to strong
magnetic turbulence, but does not significantly change the energy conversion,
reconnection rate, or particle acceleration. This study suggests that
relativistic reconnection sites are strong sources of nonthermal particles,
which may have important implications to a variety of high-energy astrophysical
problems.Comment: 18 pages, 13 figures, slightly modified after submitted to Ap
Magnetic Reconnection and Associated Particle Acceleration in High-energy Astrophysics
Magnetic reconnection occurs ubiquitously in the universe and is often
invoked to explain fast energy release and particle acceleration in high-energy
astrophysics. The study of relativistic magnetic reconnection in the
magnetically dominated regime has surged over the past two decades, revealing
the physics of fast magnetic reconnection and nonthermal particle acceleration.
Here we review these recent progresses, including the magnetohydrodynamic and
collisionless reconnection dynamics as well as particle energization. The
insights in astrophysical reconnection strongly connect to the development of
magnetic reconnection in other areas, and further communication is greatly
desired. We also provide a summary and discussion of key physics processes and
frontier problems, toward a better understanding to the roles of magnetic
reconnection in high-energy astrophysics.Comment: 49 pages, 19 figures. Submitted to Space Science Reviews. This is a
review paper as an outcome of the 2022 Magnetic Reconnection Workshop in the
International Space Science Institut
Polarization-independent phase modulation using a polymer-dispersed liquid crystal
Polarization-independent phase-only modulation of a polymer-dispersed liquid crystal (PDLC) is demonstrated. In the low voltage region, PDLC is translucent because of light scattering. Once the voltage exceeds a saturation level, PDLC is highly transparent and exhibits phase-only modulation capability. Although the remaining phase is not too large, it is still sufficient for making adaptive microdevices, such as microlens. A tunable-focus microlens for arrays using PDLC is demonstrated. This kind of microlens is scattering free, polarization independent, and has fast response time
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