28,537 research outputs found
Classical Radiation Reaction in Particle-In-Cell Simulations
Under the presence of ultra high intensity lasers or other intense
electromagnetic fields the motion of particles in the ultrarelativistic regime
can be severely affected by radiation reaction. The standard particle-in-cell
(PIC) algorithms do not include radiation reaction effects. Even though this is
a well known mechanism, there is not yet a definite algorithm nor a standard
technique to include radiation reaction in PIC codes. We have compared several
models for the calculation of the radiation reaction force, with the goal of
implementing an algorithm for classical radiation reaction in the Osiris
framework, a state-of-the-art PIC code. The results of the different models are
compared with standard analytical results, and the relevance/advantages of each
model are discussed. Numerical issues relevant to PIC codes such as resolution
requirements, application of radiation reaction to macro particles and
computational cost are also addressed. The Landau and Lifshitz reduced model is
chosen for implementation.Comment: 12 pages, 8 figure
Full-scale ab initio 3D PIC simulations of an all-optical radiation reaction configuration at
Using full-scale 3D particle-in-cell simulations we show that the radiation
reaction dominated regime can be reached in an all optical configuration
through the collision of a 1 GeV laser wakefield accelerated (LWFA)
electron bunch with a counter propagating laser pulse. In this configuration
radiation reaction significantly reduces the energy of the particle bunch, thus
providing clear experimental signatures for the process with currently
available lasers. We also show that the transition between classical and
quantum radiation reaction could be investigated in the same configuration with
laser intensities of
Simulations of particle acceleration beyond the classical synchrotron burnoff limit in magnetic reconnection: An explanation of the Crab flares
It is generally accepted that astrophysical sources cannot emit synchrotron
radiation above 160 MeV in their rest frame. This limit is given by the balance
between the accelerating electric force and the radiation reaction force acting
on the electrons. The discovery of synchrotron gamma-ray flares in the Crab
Nebula, well above this limit, challenges this classical picture of particle
acceleration. To overcome this limit, particles must accelerate in a region of
high electric field and low magnetic field. This is possible only with a
non-ideal magnetohydrodynamic process, like magnetic reconnection. We present
the first numerical evidence of particle acceleration beyond the synchrotron
burnoff limit, using a set of 2D particle-in-cell simulations of
ultra-relativistic pair plasma reconnection. We use a new code, Zeltron, that
includes self-consistently the radiation reaction force in the equation of
motion of the particles. We demonstrate that the most energetic particles move
back and forth across the reconnection layer, following relativistic Speiser
orbits. These particles then radiate >160 MeV synchrotron radiation rapidly,
within a fraction of a full gyration, after they exit the layer. Our analysis
shows that the high-energy synchrotron flux is highly variable in time because
of the strong anisotropy and inhomogeneity of the energetic particles. We
discover a robust positive correlation between the flux and the cut-off energy
of the emitted radiation, mimicking the effect of relativistic Doppler
amplification. A strong guide field quenches the emission of >160 MeV
synchrotron radiation. Our results are consistent with the observed properties
of the Crab flares, supporting the reconnection scenario.Comment: 15 pages, 16 figures, Accepted for publication in The Astrophysical
Journa
Effects of high energy photon emissions in laser generated ultra-relativistic plasmas: real-time synchrotron simulations
We model the emission of high energy photons due to relativistic charged
particle motion in intense laser-plasma interactions. This is done within a
particle-in-cell code, for which high frequency radiation normally cannot be
resolved due to finite time steps and grid size. A simple expression for the
synchrotron radiation spectra is used together with a Monte-Carlo method for
the emittance. We extend previous work by allowing for arbitrary fields,
considering the particles to be in instantaneous circular motion due to an
effective magnetic field. Furthermore we implement noise reduction techniques
and present validity estimates of the method. Finally, we perform a rigorous
comparison to the mechanism of radiation reaction, and find the emitted energy
to be in excellent agreement with the losses calculated using radiation
reaction
Kinetic simulations of relativistic magnetic reconnection with synchrotron and inverse Compton cooling
First results are presented from kinetic numerical simulations of
relativistic collisionless magnetic reconnection in pair plasma that include
radiation reaction from both synchrotron and inverse Compton (IC) processes,
motivated by non-thermal high-energy astrophysical sources, including in
particular blazars. These simulations are initiated from a configuration known
as 'ABC fields' that evolves due to coalescence instability and generates thin
current layers in its linear phase. Global radiative efficiencies, instability
growth rates, time-dependent radiation spectra, lightcurves, variability
statistics and the structure of current layers are investigated for a broad
range of initial parameters. We find that the IC radiative signatures are
generally similar to the synchrotron signatures. The luminosity ratio of IC to
synchrotron spectral components, the Compton dominance, can be modified by more
than one order of magnitude with respect to its nominal value. For very short
cooling lengths, we find evidence for modification of the temperature profile
across the current layers, no systematic compression of plasma density, and
very consistent profiles of E.B. We decompose the profiles of E.B with the use
of the Vlasov momentum equation, demonstrating a contribution from radiation
reaction at the thickness scale consistent with the temperature profile.Comment: 18 pages, 6 figures, accepted for publication in the Journal of
Plasma Physics, special collection "Plasma physics under extreme conditions:
from high-energy-density experiments to astrophysics", Eds. F. Fiuza, R. D.
Blandford & S. Glenze
Pair plasma cushions in the hole-boring scenario
Pulses from a 10 PW laser are predicted to produce large numbers of
gamma-rays and electron-positron pairs on hitting a solid target. However, a
pair plasma, if it accumulates in front of the target, may partially shield it
from the pulse. Using stationary, one-dimensional solutions of the two-fluid
(electron-positron) and Maxwell equations, including a classical radiation
reaction term, we examine this effect in the hole-boring scenario. We find the
collective effects of a pair plasma "cushion" substantially reduce the
reflectivity, converting the absorbed flux into high-energy gamma-rays. There
is also a modest increase in the laser intensity needed to achieve threshold
for a non-linear pair cascade.Comment: 17 pages, 5 figures. Accepted for publication in Plasma Physics and
Controlled Fusion. Typos corrected, reference update
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