B. Feng

QuickPIC: a highly efficient fully parallelized PIC code for plasma-based acceleration

A highly efficient, fully parallelized, fully relativistic, three-dimensional particle-incell model for simulating plasma and laser wakefield acceleration is described. The model is based on the quasi-static approximation, which reduces a fully three-dimensional electromagnetic field solve and particle push to a two-dimensional field solve and particle push. This is done by calculating the plasma wake assuming that the drive beam and/or laser does not evolve during the time it takes for it to pass a plasma particle. The complete electromagnetic fields of the plasma wake and its associated index of refraction are then used to evolve the drive beam and/or laser using very large time steps. This algorithm reduces the computation time by 2 to 3 orders of magnitude without loss of accuracy for highly nonlinear problems of interest. The code is fully parallelizable with different domain decompositions for the 2D and 3D pieces of the code. The code also has dynamic load balancing. We present the basic algorithms and design of QuickPIC, as well as comparison between the new algorithm and conventional fully explicit models (OSIRIS). Direction for future work is also presented including a software pipeline technique to further scale QuickPIC to 10,000+ processors.

Recent results and future challenges for large scale Particle-In-Cell simulations of plasma-based accelerator concepts

The concept and designs of plasma-based advanced accelerators for high energy physics and photon science are modelled in the SciDAC COMPASS project with a suite of Particle-In-Cell codes and simulation techniques including the full electromagnetic model, the envelope model, the boosted frame approach and the quasi-static model. In this paper, we report the progress of the development of these models and techniques and present recent results achieved with large-scale parallel PIC simulations. The simulation needs for modelling the plasma-based advanced accelerator at the energy frontier is discussed and a path towards this goal is outlined.

Enhancing parallel quasi-static particle-in-cell simulations with a pipelining algorithm

A pipelining algorithm to overcome the limitation on scaling quasi-static particle-in-cell models of relativistic beams in plasmas to a very large number of processors is described. The pipelining algorithm uses multiple groups of processors and optimizes the job allocation on the processors in parallel computing. The algorithm is implemented on the quasi-static code QuickPIC and is shown to scale to over 10^3 processors and increased the scale and speed by two orders of magnitude over the non-pipelined model. The new approach opens the door to performing full scale 3D simulations of future plasma wakefield accelerators or full lifetime models of beam interaction with electron clouds in circular accelerators such as the Large Hadron Collider (LHC) at CERN.

Enhancing Plasma Wakefield and E‐cloud Simulation Performance Using a Pipelining Algorithm

Modeling long timescale propagation of beams in plasma wakefield accelerators at the energy frontier and in electron clouds in circular accelerators such as CERN‐LHC requires faster and more efficient simulation codes. Simply increasing the number of processors does not scale beyond one‐fifth of the number of cells in the decomposition direction. A pipelining algorithm applied on fully parallelized code QuickPIC is suggested to overcome this limit. The pipelining algorithm uses many groups of processors and optimizes the job allocation on the processors in parallel computing. With the new algorithm, it is possible to use on the order of 102 groups of processors, expanding the scale and speed of simulations with QuickPIC by a similar factor.

Long Time Simulation of LHC Beam Propagation in Electron Clouds

In this report we show the simulation results of single-bunch instabilities caused by interaction of a proton beam with an electron cloud for the Large Hadron Collider (LHC) using the code QuickPIC [1]. We describe three new results: 1) We test the effect of the space charge of the beam on itself; 2) we add the effect of dispersion in the equation of motion in the x direction, and 3) we extend previous modeling by an order of magnitude (from 50ms to 500ms) of beam circulation time. The effect of including space charge is to change the emittance growth by less than a few percent. Including dispersion changes the plane of instability but keeps the total emittance approximately the same. The longer runs indicate that the long term growth of electron cloud instability of the LHC beam cannot be obtained by extrapolating the results of short runs.

Simulation Of Electron Cloud Effects On Electron Beam At ERL With Pipelined QuickPIC

With the successful implementation of pipelining algorithm to the QuickPIC code, the number of processors used is increased by 2 to 3 orders of magnitude, and the speed of the simulation is improved by a similar factor. The pipelined QuickPIC is used to simulate the electron cloud effect on electron beam in the Cornell Energy Recovery Linac (ERL) due to extremely small emittance and high peak currents anticipated in the machine. A tune shift is found due to electron cloud on electron beams, which is of equal magnitude to that on positron beams but in an opposite direction; however, emittance growth of the electron beam in an electron cloud is not observed for ERL parameters.

Simulation of Weibel Instability for LWFA and PWFA Electron Beams

Weibel instability is of central importance for relativistic beams both in laboratory, ex. fast‐igniter concept for inertial confinement fusion, and astrophysical, ex. cosmic jets, plasmas. Simulations, using QuickPIC, of an intense and monoenergetic beam propagating through a plasma were conducted for experimental setups with Laser Wakefield and RF accelerators and show the appearance of Weibel instability (or current instability). The appearance of the instability is investigated as a function of beam parameters (density, spot size and bunch length) and plasma parameters (plasma density and length of plasma). We present preliminary simulation results that show that the instability should be observable for the RF accelerator experiment.