13,437 research outputs found
Controlled Shock Shells and Intracluster Fusion Reactions in the Explosion of Large Clusters
The ion phase-space dynamics in the Coulomb explosion of very large ( atoms) deuterium clusters can be tailored using two consecutive
laser pulses with different intensities and an appropriate time delay. For
suitable sets of laser parameters (intensities and delay), large-scale shock
shells form during the explosion, thus highly increasing the probability of
fusion reactions within the single exploding clusters. In order to analyze the
ion dynamics and evaluate the intracluster reaction rate, a one-dimensional
theory is used, which approximately accounts for the electron expulsion from
the clusters. It is found that, for very large clusters (initial radius
100 nm), and optimal laser parameters, the intracluster fusion yield becomes
comparable to the intercluster fusion yield. The validity of the results is
confirmed with three-dimensional particle-in-cell simulations.Comment: 25 pages, 11 figures, to appear in Physical Review
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
Modelling radiation emission in the transition from the classical to the quantum regime
An emissivity formula is derived using the generalised
Fermi-Weizacker-Williams method of virtual photons which accounts for the
recoil the charged particle experiences as it emits radiation. It is found that
through this derivation the formula obtained by Sokolov et al using QED
perturbation theory is recovered. The corrected emissivity formula is applied
to nonlinear Thomson scattering scenarios in the transition from the classical
to the quantum regime, for small values of the nonlinear quantum parameter
\chi. Good agreement is found between this method and a QED probabilistic
approach for scenarios where both are valid. In addition, signatures of the
quantum corrections are identified and explored.Comment: 11 pages, 4 figures, submitted for publicatio
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
Particle Merging Algorithm for PIC Codes
Particle-in-cell merging algorithms aim to resample dynamically the
six-dimensional phase space occupied by particles without distorting
substantially the physical description of the system. Whereas various
approaches have been proposed in previous works, none of them seemed to be able
to conserve fully charge, momentum, energy and their associated distributions.
We describe here an alternative algorithm based on the coalescence of N massive
or massless particles, considered to be close enough in phase space, into two
new macro-particles. The local conservation of charge, momentum and energy are
ensured by the resolution of a system of scalar equations. Various simulation
comparisons have been carried out with and without the merging algorithm, from
classical plasma physics problems to extreme scenarios where quantum
electrodynamics is taken into account, showing in addition to the conservation
of local quantities, the good reproducibility of the particle distributions. In
case where the number of particles ought to increase exponentially in the
simulation box, the dynamical merging permits a considerable speedup, and
significant memory savings that otherwise would make the simulations impossible
to perform
Magnetically assisted self-injection and radiation generation for plasma based acceleration
It is shown through analytical modeling and numerical simulations that
external magnetic fields can relax the self-trapping thresholds in plasma based
accelerators. In addition, the transverse location where self-trapping occurs
can be selected by adequate choice of the spatial profile of the external
magnetic field. We also find that magnetic-field assisted self-injection can
lead to the emission of betatron radiation at well defined frequencies. This
controlled injection technique could be explored using state-of-the-art
magnetic fields in current/next generation plasma/laser wakefield accelerator
experiments.Comment: 7 pages, 4 figures, accepted for publication in Plasma Physics and
Controlled Fusio
Radiation in 1.5 GeV and 12 GeV laser wakefield acceleration stages from PIC simulations
WOS:000287176200029 (Nº de Acesso Web of Science)A massivelly parallel post-processing radiation diagnostic for PIC codes is presented, which is then used to study the main features of the radiation from single LWFA stages (1.5 GeV and 12 GeV). This diagnostic also allows to examine radiation signatures associated with the physics of self-injection
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