Paper  Title  Page 

TUSBC1 
Simulating Radiation from Laserwakefield Accelerators  


Radiation from laserwakefield accelerators (LWFA), ranging from the xray to the infrared spectrum, is of great interest for experiments, both for advanced diagnostics and radiation sources. Hence, detailed numerical modelling of these phenomena is desired for understanding measured data. In order to meet computational demands, we build on recent advances in general purpose graphical processing units (GPGPU). With the PIConGPU code, a scalable, highlyparallel, performant implementation of a 3DPIC code [1], it is possible to run largescale, realistic simulations within hours compared to more than a week on CPUs. Here we present, a LiénardWiecherttype radiation algorithm (CLARA) as an extension to PIConGPU, which now can calculate the plasma radiation spectrum in all directions of the solid angle, parallel to the laserplasma simulation, when the full macroparticle data is in memory. We discuss the algorithm with its tradeoffs between data storage and computation time on GPUs and CPUs. As examples, we display first results from realistic laserwakefield accelerator scenarios investigated using the DRACO laser system at the HZDR.
[1] H Burau, et al, "PIConGPU: A Fully Relativistic ParticleinCell Code for a GPU Cluster", IEEE Transactions on Plasma Science 38(10), 28312839 (October 2010) 

Slides TUSBC1 [10.019 MB]  
TUSBC2  Low Noise ParticleinCell Simulations of Laser Plasma Accelerator 10 GeV Stages  78 


Funding: Work supported by DOE/HEP, under grants DESC0004441 and DEFC0207ER41499, including use of NERSC under DEAC0205CH11231. Because of their ultrahigh accelerating gradient, laser plasma based accelerators (LPA) are contemplated for the next generation of highenergy colliders and light sources. The upcoming BELLA project will explore acceleration of electron bunches to 10 GeV in a 1 meter long plasma, where a wakefield is driven by a PWclass laser. Particleincell (PIC) simulations are used to design the upcoming experiments where boosted frame simulations are used to model the full scale stages. As criteria on energy spread and beam emittance become more stringent, PIC simulations become more challenging as high frequency noise artificially increases those quantities. We show that calculating the beam selffields using a static Poisson solve in the beam frame dramatically reduces particle noise, allowing for more accurate simulation of the beam evolution. In particular, this method gets correct cancellation of the transverse selfelectric and magnetic fields of the beam, eliminating artificial selfforces, which is usually not true when using the standard PIC algorithm based on the staggered (“Yee”) electromagnetic field solver. 

Slides TUSBC2 [5.989 MB]  
TUSBC3 
Improved Particle Statistics for LaserPlasma SelfInjection Simulations  


Funding: Work supported by Contracts DOE DESC0006245, DEFC0207ER41499, DEFG0208ER55000, and DEFG0205ER15663; NSF PHY1104683; DTRA HDTRA111C0001; and AFOSR FA95501110157 and 95500810232. Simulations of laserplasma acceleration (LPA) play a key role in understanding the effect of initial conditions on injected beam parameters. Here we present a method for improving the accuracy of simulated particle beams from the LPA selfinjection process. We recently demonstrated the ability to compute the collection volume of an injection process – the range of initial locations of injected particles*. We find that the collection volume consists of an annular region around the propagation axis. By loading this region with higher particle statistics than in other locations, we can significantly increase the number of macroparticles in the injected beam. We show that this technique captures much finer detail of particle phase space than does uniform loading, and results in lower noise. We demonstrate convergence of key beam parameters in 2D, and present results of full 3D simulations. In addition, we present results of a novel technique in which particles can deform and split if they expand, effectively selfgenerating statistics. We also discuss a perfect dispersion algorithm and its impact on selfinjection results. *B. M. Cowan et al., "Computationally efficient methods for modelling laser wakefield acceleration in the blowout regime," accepted for publication in J. Plasma Phys. (2012) 

Slides TUSBC3 [6.516 MB]  
THAAI2  Efficient Modeling of Laserplasma Accelerators Using the Ponderomotivebased Code INF&RNO  206 


Funding: Work supported by the Office of Science, Office of High Energy Physics, of the U.S. Department of Energy under Contract No. DEAC0205CH11231. Numerical modeling of laserplasma accelerators using the ponderomotive approximation allows efficient modeling of 10 GeV and beyond laserplasma accelerators. The timeaveraged ponderomotive force approximation also allows simulation in cylindrical geometry which captures relevant 3D physics at 2D computational cost. In this talk I will present the code INF&RNO (INtegrated Fluid & paRticle simulatioN cOde). The code is based on an envelope model for the laser while either a PIC or a fluid description can be used for the plasma. The effect of the laser pulse on the plasma is modeled with the timeaveraged poderomotive force. These and other features, such as dynamical resampling of the phase space distribution to reduce onaxis noise and boostedLorentzframe modeling capability, allow for a speedup of several orders of magnitude compared to standard full PIC simulations while still retaining physical fidelity. The code has been benchmarked against analytical solutions and 3D PIC simulations and a set of validation tests together with a discussion of the performances will be presented. Applications to the BELLA PW laserplasma accelerator experiments at LBNL will be discussed. 

Slides THAAI2 [1.881 MB]  
THP08  Beam Dynamics Studies for Particle Driven Plasma Wakefield Acceleration Experiments at PITZ  236 


The Photo Injector Test Facility at DESY, Zeuthen site (PITZ) is developing and optimizing high brightness electron sources for linac based free electron lasers such as FLASH and the European XFEL. The high quality of the 25 MeV electron beam together with the availability of a highly flexible photocathode laser system makes the PITZ injector a perfect facility for variety of experimental studies. Two approaches are of great interest for future applications in the context of particle driven plasma wakefield acceleration experiments: selfmodulation and transformer ratio studies. In both cases a high density electron beam is interacting with a plasma which has a density of about 10^{15} cm^{3}. ASTRA simulations were done to study the ebeam density along the existing PITZ beamline, especially at two different possible longitudinal positions of the planned plasma cell, in order to reach the particle density required for occurrence of selfmodulation. The results of the beam dynamics studies are presented and discussed in this paper.  