32 research outputs found
QScatter: Numerical Framework for Fast Prediction of Particle Distributions in Electron-Laser Scattering
The new generation of multi-PetaWatt laser facilities will allow tests of
Strong Field QED, as well as provide an opportunity for novel photon and lepton
sources. The first experiments are planned to study the (nearly) head-on
scattering of intense, focused laser pulses with either relativistic electron
beams or high-energy photon sources. In this work, we present a numerical
framework that can provide fast predictions of the asymptotic particle and
photon distributions after the scattering. The works presented in this
manuscript includes multiple features such as spatial and temporal misalignment
between the laser and the scattering beam, broadband electron beams, and beam
divergence. The expected mean energy, energy spread, divergence or other
observables are calculated by combining an analytical description and numerical
integration. This method can provide results within minutes on a personal
computer, which would otherwise require full-scale 3D QED-PIC simulations using
thousands of cores. The model, which has been compiled into an open-source code
QScatter, may be used to support the analysis of large-size data sets from
high-repetition rate experiments, leveraging its speed for optimization or
reconstruction of experimental parameters.Comment: 17 pages, 9 figure
Electron - positron cascades in multiple-laser optical traps
We present an analytical and numerical study of multiple-laser QED cascades
induced with linearly polarised laser pulses. We analyse different polarisation
orientations and propose a configuration that maximises the cascade
multiplicity and favours the laser absorption. We generalise the analytical
estimate for the cascade growth rate previously calculated in the field of two
colliding linearly polarised laser pulses and account for multiple laser
interaction. The estimate is verified by a comprehensive numerical study of
four-laser QED cascades across a range of different laser intensities with QED
PIC module of OSIRIS. We show that by using four linearly polarised 30 fs laser
pulses, one can convert more than 50 % of the total energy to gamma-rays
already at laser intensity . In this
configuration, the laser conversion efficiency is higher compared with the case
with two colliding lasers
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
Radiation-dominated injection of positrons generated by the nonlinear Breit-Wheeler process into a plasma channel
Plasma acceleration is considered a prospective technology for building a
compact multi-TeV electron-positron collider in the future. The challenge of
this endeavor is greater for positrons than for the electrons because usually
the self-generated fields from laser-plasma interaction are not well-suited for
positron focusing and on-axis guiding. In addition, an external positron source
is required, while electrons are naturally available in the plasma. Here, we
study electron-positron pair generation by an orthogonal collision of a
multi-PW laser pulse and a GeV electron beam by the nonlinear Breit-Wheeler
process. We studied conditions favorable for positron deflection in the
direction of the laser pulse propagation, which favors injection into the
plasma for further acceleration. We demonstrate using the OSIRIS
particle-in-cell framework that the radiation reaction triggered by ultra-high
laser intensity plays a crucial role in the positron injection. It provides a
suppression of the initial transverse momentum gained by the positrons from the
Breit-Wheeler process. For the parameters used in this work, the intensity of
at least 2.2x1023 W/cm2 is needed in order to inject more than 1% of positrons
created. Above this threshold, the percentage of injected positrons rapidly
increases with intensity. Moreover, subsequent direct laser acceleration of
positrons in a plasma channel, using the same laser pulse that created them,
can ensure a boost of the final positron energy by a factor of two. The
positron focusing and guiding on the axis is provided by significant electron
beam loading that changes the internal structure of the channel fields
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
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