Study of plasma wakefield acceleration mechanism for emittance dominated regimes via hybrid and pic simulations

Electron plasma wakefield acceleration (PWFA) mechanism is a promising non conventional acceleration scheme. Nonetheless further investigation is still needed to fully uncover the instability mechanisms so to mitigate them and make PWFA an effective tool. This work focuses in this direction, we discuss the necessity to use well matched driver bunches to further mitigate witness instabilities. Specifically we propose to inject driver bunches with larger emittance than the matched one (overcompressed bunch) so to let the system reach the matching condition by itself. This preliminary results lead us to the following consideration: while a limited number of cases can be studied with a particle-in-cell code, we understand the necessity for fast systematic analysis: we briefly introduce the hybrid code Architect

High energy gain in three-dimensional simulations of light sail acceleration

The dynamics of radiation pressure acceleration in the relativistic light sail regime are analysed by means of large scale, three-dimensional (3D) particle-in-cell simulations. Differently to other mechanisms, the 3D dynamics leads to faster and higher energy gain than in 1D or 2D geometry. This effect is caused by the local decrease of the target density due to transverse expansion leading to a “lighter sail.” However, the rarefaction of the target leads to an earlier transition to transparency limiting the energy gain. A transverse instability leads to a structured and inhomogeneous ion distributio

Errors, Correlations and Fidelity for noisy Hamilton flows. Theory and numerical examples

International audienceWe compare the decay of correlations and fidelity for some prototype noisy Hamiltonian flows on a compact phase space. The results obtained for maps on the torus T2 or on the cylinder T×I are recovered, in a simpler way, in the limit of vanishing time step Δt→0, if these maps are the symplectic integrators of the proposed flows. The mean square deviation σ(t) of the noisy flow asymptotically diverges, following a power law if the unperturbed flow is integrable, exponentially if it is chaotic. Correspondingly the fidelity, which measures the correlation at time t of the noisy flow with respect to unperturbed flow, decays as exp(−2π2σ2(t)). For chaotic flows the fidelity exhibits a plateau, followed by a super-exponential decay starting at t∗∝−logϵ where ϵ is the noise amplitude. We analyze numerically two simple models: the anharmonic oscillator the H\'enon-Heiles Hamiltonian and the N vortex system for N=3,4 The round-off error on the symplectic integrator acts as a (single realization of a) random perturbation provided that the map has a sufficiently high computational complexity. This can be checked by considering the reversibility error. Finally we consider the effect of the observational noise showing that the decrease of correlations or fidelity can only be observed, after a sequence of measurements. The multiplicative noise is more effective at least for long enough delay between two measurements

Towards Robust Algorithms for Current Deposition and Dynamic Load-Balancing in a GPU Particle In Cell Code

We present 'jasmine', an implementation of a fully relativistic, 3D, electromagnetic Particle-In-Cell (PIC) code, capable of running simulations in various laser plasma acceleration regimes on Graphics-Processing-Units (GPUs) HPC clusters. Standard energy/charge preserving FDTD-based algorithms have been implemented using double precision and quadratic (or arbitrary sized) shape functions for the particle weighting. When porting a PIC scheme to the GPU architecture (or, in general, a shared memory environment), the particle-to-grid operations (e. g. the evaluation of the current density) require special care to avoid memory inconsistencies and conflicts. Here we present a robust implementation of this operation that is efficient for any number of particles per cell and particle shape function order. Our algorithm exploits the exposed GPU memory hierarchy and avoids the use of atomic operations, which can hurt performance especially when many particles lay on the same cell. We show the code multi-GPU scalability results and present a dynamic load-balancing algorithm. The code is written using a python-based C++ meta-programming technique which translates in a high level of modularity and allows for easy performance tuning and simple extension of the core algorithms to various simulation schemes

Case studies in space charge and plasma acceleration of charged beams

none5siPlasma acceleration with electron or proton driver beams is a challenging opportunity for high-energy physics. An energy doubling experiment with electron drivers was successfully performed at SLAC and a key experiment AWAKE with proton drivers is on schedule at CERN. Simulations play an important role in choosing the best experimental conditions and in interpreting the results. The Vlasov equation is the theoretical tool to describe the interaction of a driver particle beam or a driver laser pulse with a plasma. Collective effects, such as tune shift and mismatch instabilities, appear in high intensity standard accelerators and are described by the Poisson–Vlasov equation. In the paper, we review the Vlasov equation in the electrostatic and fully electromagnetic cases. The general framework of variational principles is used to derive the equation, the local form of the balance equations and related conservation laws. In the electrostatic case, we remind the analytic Kapchinskij–Vladimirskij (K–V) model and we propose an extension of the adiabatic theory for Hamiltonian systems, which ensures stability for perturbation of size ϵ on times of order 1/ϵ1/ϵ. The variational framework is used to derive the Maxwell–Vlasov equations and related conservation laws and to briefly sketch the particle-in-cell (PIC) approximation schemes. Finally, the proton-driven acceleration is examined in the linear and quasi-linear regime. A PIC simulation with the code ALaDyn developed at Bologna University is presented to illustrate the longitudinal and transverse fields evolution which allow a witness electron bunch to be accelerated with a gradient of a few GeV/m. We also present some remarks on future perspectives.mixedArmando Bazzani;Massimo Giovannozzi;Pasquale Londrillo;Stefano Sinigardi;Giorgio TurchettiArmando Bazzani;Massimo Giovannozzi;Pasquale Londrillo;Stefano Sinigardi;Giorgio Turchett

Errors, Correlations and Fidelity for noisy Hamilton flows. Theory and numerical examples

International audienceWe compare the decay of correlations and fidelity for some prototype noisy Hamiltonian flows on a compact phase space. The results obtained for maps on the torus T2 or on the cylinder T×I are recovered, in a simpler way, in the limit of vanishing time step Δt→0, if these maps are the symplectic integrators of the proposed flows. The mean square deviation σ(t) of the noisy flow asymptotically diverges, following a power law if the unperturbed flow is integrable, exponentially if it is chaotic. Correspondingly the fidelity, which measures the correlation at time t of the noisy flow with respect to unperturbed flow, decays as exp(−2π2σ2(t)). For chaotic flows the fidelity exhibits a plateau, followed by a super-exponential decay starting at t∗∝−logϵ where ϵ is the noise amplitude. We analyze numerically two simple models: the anharmonic oscillator the H\'enon-Heiles Hamiltonian and the N vortex system for N=3,4 The round-off error on the symplectic integrator acts as a (single realization of a) random perturbation provided that the map has a sufficiently high computational complexity. This can be checked by considering the reversibility error. Finally we consider the effect of the observational noise showing that the decrease of correlations or fidelity can only be observed, after a sequence of measurements. The multiplicative noise is more effective at least for long enough delay between two measurements