53,199 research outputs found
Electromagnetic field generation in the downstream of electrostatic shocks due to electron trapping
A new magnetic field generation mechanism in electrostatic shocks is found,
which can produce fields with magnetic energy density as high as 0.01 of the
kinetic energy density of the flows on time scales . Electron trapping during the shock formation process
creates a strong temperature anisotropy in the distribution function, giving
rise to the pure Weibel instability. The generated magnetic field is
well-confined to the downstream region of the electrostatic shock. The shock
formation process is not modified and the features of the shock front
responsible for ion acceleration, which are currently probed in laser-plasma
laboratory experiments, are maintained. However, such a strong magnetic field
determines the particle trajectories downstream and has the potential to modify
the signatures of the collisionless shock
Physics of collisionless shocks - theory and simulation
Collisionless shocks occur in various fields of physics. In the context of
space and astrophysics they have been investigated for many decades. However, a
thorough understanding of shock formation and particle acceleration is still
missing. Collisionless shocks can be distinguished into electromagnetic and
electrostatic shocks. Electromagnetic shocks are of importance mainly in
astrophysical environments and they are mediated by the Weibel or filamentation
instability. In such shocks, charged particles gain energy by diffusive shock
acceleration. Electrostatic shocks are characterized by a strong electrostatic
field, which leads to electron trapping. Ions are accelerated by reflection
from the electrostatic potential. Shock formation and particle acceleration
will be discussed in theory and simulations
The impact of kinetic effects on the properties of relativistic electron-positron shocks
We assess the impact of non-thermally shock-accelerated particles on the
magnetohydrodynamic (MHD) jump conditions of relativistic shocks. The adiabatic
constant is calculated directly from first principle particle-in-cell
simulation data, enabling a semi-kinetic approach to improve the standard fluid
model and allowing for an identification of the key parameters that define the
shock structure. We find that the evolving upstream parameters have a stronger
impact than the corrections due to non-thermal particles. We find that the
decrease of the upstream bulk speed yields deviations from the standard MHD
model up to 10%. Furthermore, we obtain a quantitative definition of the shock
transition region from our analysis. For Weibel-mediated shocks the inclusion
of a magnetic field in the MHD conservation equations is addressed for the
first time
Orbit decidability, applications and variations
We present the notion of orbit decidability into a more general framework,
exploring interesting generalizations and variations of this algorithmic
problem. A recent theorem by Bogopolski-Martino-Ventura gave a renovated
protagonism to this notion and motivated several interesting algebraic
applications
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