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High performance modeling tools for plasma-based accelerators

High performance modeling tools for plasma-based accelerators. C. Benedetti, J.-L. Vay, C.B. Schroeder, R. Lehe, C.G.R. Geddes, E. Esarey, & W.P. Leemans BELLA Center, LBNL. FACET-II Science Opportunities Workshops SLAC, October 12-16, 2015.

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High performance modeling tools for plasma-based accelerators

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  1. High performance modeling tools for plasma-based accelerators C. Benedetti, J.-L. Vay, C.B. Schroeder, R. Lehe, C.G.R. Geddes, E. Esarey, & W.P. Leemans BELLA Center, LBNL FACET-II Science Opportunities Workshops SLAC, October 12-16, 2015 Work supported by Office of Science, US DOE, Contract No. DE-AC02-05CH11231

  2. Overview • Requirements for an end-to-end modeling of a laser-plasma accelerator (LPA)-based linear collider [or a driver for an advanced light source (e.g., LPA-based FEL)] • BLAST (Berkeley Lab Accelerator Simulation Toolkit) modules as a comprehensive suite of numerical tools for efficient, detailed and predictive modeling of intense laser-plasma interactions: • Ultra-low emittance from two-color laser ionization injection [injector] • Current BELLA experiments: 4.3 GeV LPA (using 16 J) [LPA stage] • Future BELLA experiments: 10 GeV LPA stage [LPA stage] • Staging experiment [LPA staging] • Summary 2

  3. Many potential LPA applications require high repetition rate and high wall-plug efficiency End-to-end simulation of a plasma-based linear collider is an extremely challenging problem (multi-physics, multi-scale) • All-optical setup (injection+acceleration) • 100x10 GeV LPA modules (staging) • Length: ≤1 Km (1-10 GV/m) VS ~30 Km of ILC (RF, ~50 MV/m) LPA-based collider* → Injector: - gas dynamics - bunch self-injection (10 GeV, 1 m) LPA-stage: - gas dynamics - MHD - laser-plasma interaction Driver in-coupling Beam transport - vacuum propag. - lenses - interaction w/plasma mirror Final focus Positron generation - Montecarlo code *Leemans, Esarey, Physics Today (2009) Schroeder et al., PRSTAB (2010) 3

  4. Many potential LPA applications require high repetition rate and high wall-plug efficiency LBNL is developing a suite of tools to addresses the diverse physics of interest to model an LPA-based collider 4

  5. Computational complexity in modeling an LPA stage depends on unbalance between physical scales involved in the simulation Maxwell-Vlasov equations → Particle-In-Cell (PIC) scheme: spatial grid for EM fields + macroparticles for plasma plasmawaves λp λ0 e-bunch laser pulse *courtesy of B. Shadwick et al. L Simulation complexity scales ~ (D/λ0)4/3 → 3D full PIC simulation of a 10 GeV LPA stage (~109 grid points, >109 macroparticles, 107 time steps) requires: 107 -108 CPUh → UNFEASIBLE WITH CONVENTIONAL 3D PIC CODES ← 5

  6. Understanding the physics of intense LPAs requires detailed numerical modeling What we need (from the computational point of view): • run 3D simulations (dimensionality matters!) of cm/m-scale laser-plasma interaction in a reasonable time (a few hours/days) • perform, for a given problem, different simulations (exploration of the parameter space, optimization, convergence check, etc.) Reduced Models → Reducing the computational complexity by carefully selecting the amount of Information/physics to compute (e.g., by neglecting some aspects of the physics) Lorentz Boosted Frame→ Different spatial/temporal scales in an LPA simulation do not scale the same way changing the reference frame. Simulation length can be greatly reduced going to an optimal (wake) reference frame. Mora & Antonsen, Phys. Plas. (1997) [WAKE] Huang, et al., JCP (2006) [QuickPIC] Lifshitz, et al., JCP (2009) [CALDER-circ] Benedetti, et al., AAC2010/PAC2011/ICAP2012 [INF&RNO] Mehrling, et al., PPCF (2014) [HiPACE] Vay, PRL (2007) 6

  7. Berkeley Lab Accelerator Simulation Toolkit (BLAST) provides comprehensive suite of numerical tools for detailed, efficient, and predictive modeling of advanced accelerators Detailed modeling of: beams, plasmas, laser-plasma interaction, linacs, rings, injectors, LPAs, … Using state-of-the-art codes: BEAMBEAM3D, IMPACT, POSINST, INF&RNO, WARP With original advanced algorithms: boosted frame, IGF, advanced laser envelope, AMR, relativistic particle pusher, EM spectral, quasi-cylindrical, … Reduced code tailored on LPAs: several orders of magnitude faster compared to 3D full PIC General purpose, full 3D PIC: more complete description. Large gain with boosted frame. 2014 & 2015 NERSC HPC Achievement award; 2013 USPAS Prize http://blast.lbl.gov 7

  8. Tunnel ionization implemented in BLAST modules and used to investigate novel concept to produce ultra-low emittance beam using two-color laser ionization injection* Modeling injector → >0=trapping Transverse phase space Low emittance injected beam Plasma Pump laser pulse Wake Injection laser pulse εn ≈ 0.028 μm Simulations: Warp Visualization: VisIt *Yu, et al., PRL (2014)Schroeder, et al., PRSTAB (2014) Schroeder, et al., SPIE Proc (2015) 8

  9. INF&RNO is used to model current BELLA experiments: study of laser evolution in a 9 cm capillary* using realistic model for laser pulse 1/e2 intensity 0 3 6 9 0 3 6 9 Accurate model of the BELLA laser has been constructed based on measurements transverse intensity profile based on exp data 2013 measured long. laser intensity profile – top-hat near field: I/I0=[2J1(r/R)/(r/R)]2– Gaussian Ulaser=15 J Simulation cost w/ INF&RNO: ~10 CPUh (reduction ~106) → features of INF&RNO allowed to run many simulations at a reasonable computational cost 9 Propagation distance (cm) *Leemans, et al., PRL (2014) 9

  10. Post-interaction laser optical spectra have been used as an independent diagnostic of the on-axis density* Comparison between measured and simulated post-interaction laser optical spectra Measurement INF&RNO simulation *Simulations include instrumental response ← 30 simulation runs (each for a 9 cm long LPA) → numerical modeling reproduces key features in the laser optical spectra: independent diagnostic for the plasma density *Leemans, et al., PRL (2014) 10

  11. INF&RNO full PIC simulation allows for detailed investigation of particle self-injection and acceleration Simulated spectra *Leemans, et al., PRL (2014) E=4.3 GeVdE/E=13%Q=50 pC x'=0.2 mrad e-beam spectrum [nC/SR/(MeV/c)] E=4.2 GeVdE/E=6%Q=6 pC x'=0.3 mrad Experiment divergence [mrad] Simulation cost w/ INF&RNO: 300,000 CPUh (reduction >200) 11 Energy [GeV]

  12. WARP allows for efficient modeling of meter long, 10 GeV LPA stages using Lorentz boosted frame* e- beam energy gain (GeV) Simulation speed-up e- beam position (m) γ (Lorentz boost speed) e- beam size (μm) e- beam position (m) → Theoretical speedups demonstrated numerically Simulation cost 10 GeV LPA (3D) w/ WARP: 5,000 CPUh using LBF (reduction ~20,000) *J.-L. Vay, PRL (2007) 12

  13. INF&RNO is used to design and help the interpretation of the results of the STAGING experiment* Modeling of e-bunch spectrum after LPA2 as a function of the delay between e-bunch and laser2 at the entrance of LPA2 plasma mirror Simulation cost w/ INF&RNO: ~15 CPUh (reduction ~60,000) bunch LPA1 Laser1 (1.3 J, 45 fs) LPA2 Laser2 (0.45 J, 45 fs) cap lens Measurement* INF&RNO simulation ← 550 simulation runs (each for a 3.3 cm long LPA) +100 MeV energy gain, 3% capturing efficiency in LPA2 → *background subtracted 13 *Steinke, et al., submitted (2015)

  14. Many potential LPA applications require high repetition rate and high wall-plug efficiency ~10 GeV electron beams from STAGING experiment using BELLA (5 GeV+5 GeV): simulations show 100% capturing efficiency Energy spectra ← injector 8 cm 1 cm 10 cm 20 cm ~30 cm ~30 cm injector cap lens after LPA1 LPA2 [n0=(2-3)x1017cm-3] LPA1 [n0=(2-3)x1017cm-3] Laser1 =BELLA/2 (15 J, 80 fs) after LPA2 bunch Laser2 =BELLA/2 (15 J, 80 fs) Bunch dynamics in LPA1 Bunch transport LPA1 → LPA2 Bunch dynamics in LPA2 delay=-434.6 fs delay=-430.8 fs delay=-426.9 fs 5 GeV bunch from LPA1 refocused: 100% bunch captured in LPA2 Bunch energy Bunch energy Relative energy spread Relative energy spread cap lens 14

  15. Continuous development of new modules within BLAST for improved accuracy/physical fidelity New WARP Module* (R. Lehe) = spectral + quasi-cylindrical PIC Two-fold improvement in the physical fidelity/accuracy: Quasi-cylindrical: possibility to model non-axisymmetric physics Spectral: strongly reduces spurious Cherenkov radiation (e.g., better description of beam emittance) (addition of a few azimuthal modes) (eqs. solved in Fourier space) Numerical error → Ported on GPU (40x speed-up) *Lehe et al., submitted to CPC (2015) 15

  16. Summary and future research directions • BLAST modules will allow modeling all the aspects of an LPA-based collider • Our numerical tools are accurate: we are benchmarking/validating our simulation tools against current experiments at LBNL • Our numerical tools are efficient: our codes provides computational speed-ups of several orders of magnitude compared to conventional 3D PIC codes • Modeling using BLAST modules guides the design of current experiments and enables testing of new advanced accelerator concepts • Future research directions: • Exploring and developing reduced models to capture relevant physics • Continue developing numerical schemes for improved efficiency/fidelity • Combine different approaches to increase speedup • Improving the parallel efficiency exploiting new hardware (GPUs, many-cores) 16

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