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Full-scale particle simulations of highenergy density science experiments W.B.Mori , W.Lu, M.Tzoufras, B.Winjum, J.Fahlen,F.S.Tsung, C.Huang,J.Tonge M.Zhou, V.K.Decyk, C. Joshi (UCLA) L.O.Silva, R.A.Fonseca (IST Portugal) C.Ren (U. Rochester) T. Katsouleas (USC) Directed high-energy density Lasers • Pressure=Energy/Volume – Pressure=Power/Area/c • PetaWatt with 10mm spot – 3x1010 J/cm3 – 300 GBar • Electric field in laser: Particle beams • At SLAC: – N=2x1010 e- or e+ sr=1mm, sz =60mm – E=50GeV • Pressure: – 15x1010J/cm3 – 1.5TBar – TeV/cm • Electric field of beam: – 1.6TeV/cm Radiation pressure and space forces of intense lasers and beams expel plasma electrons Particle Accelerators Why Plasmas? Conventional Accelerators • Limited by peak power and breakdown Plasma • No breakdown limit • 20-100 MeV/m • 10-100 GeV/m Why lasers? Radiation pressure can excite longitudinal wakes a0 eA 10 2 8.5x10 I(W /cm )mm 2 mc Concepts For Plasma Based Accelerators* Plasma Wake Field Accelerator(PWFA) A high energy electron bunch Laser Wake Field Accelerator(LWFA, SMLWFA, PBWA) A single short-pulse of photons Drive beam 1. Wake excitation 2. Evolution of driver and wake 3. Loading the wake with particles *Tajima and Dawson PRL 1979 Trailing beam Plasma Accelerator Progress and the “Accelerator Moore’s Law” Slide 2 LOA,RAL LBL ,RAL Osaka Courtesy of Tom Katsouleas The blowout and Rosenzwieg et al. 1990 bubble regimes Puhkov and Meyer-te-vehn 2002 Ion column provides ideal accelerating and focusing forces Full scale 3D particle-in-cell modeling is now possible:OSIRIS Typical simulation parameters: ~109 particles ~105 time steps Other codes:VLPL, Vorpal, TurboWAVE, Z3 etc., but no all the same! Progress in computer hardware The “Dawson” cluster at UCLA: <$1,000,000 $50,000,000 Progress in lasers Courtesy of G.Mourou Progress in hardware and software • Era Memory particles speed max energy (full PIC) •80’s 16MByte 105-106 5ms/part-step 100 MeV (2D) ~109 1x10-3ms/part-step 1-10GeV (3D (~7.5 Tflops/3) •Local ~500GByte Clusters (e.g., DAWSON) ~109 2x10-3 ms/part-step 1-10GeV (3D) (2.3Tflops) 1 TeV (3D) •Future 25-1000TByte >1011 5x10-5ms/part-step 500 GeV (3D) 150Tflops - 10Pflops? •Today ~6TByte/3 (e.g., NERSC) The simulations of Tajima and Dawson would take ~1 second on my laptop! Computational challenges for modeling plasma-based acceleration (1 GeV Stage) Beam-driven wake* z y, x t # grids in z # grids in x , y # steps Nparticles Particles x steps Fully Explicit .05 c/p .05 c/p .02 c/p 350 150 2 x 10 5 ~.25 x 1 08 (3D) ~1 x 10 6 (2D) ~.5 x 1013 (3D) - 10,000 hrs ~1 x 10 11 (2D) - 75 hrs *Laser-driven GeV stage requires on the o rder of (o/p)2=1000 x l onger, however, the the resolution ca n usually be relaxed. Full-scale modeling: Challenges and expectations Challenges: What is excellent agreement? • As a laser propagates through• Don’t know exact plasma the plasma it encounters profile. ~1013-1014 electrons • Don’t know laser intensity or spot size. • There are ~106-109 selftrapped electrons • Don’t know laser transverse, longitudinal, or frequency • Need to model accuracy of 1 profile (not a diffraction 6 part in O(10 ) limited Gaussian beam). Convergence of advances in laser technology and computer simulation Full scale 3D LWFA simulation using OSIRIS: 6TW, 50fs State-of- the- art ultrashort laser pulse 0 = 800 nm, t = 50 fs •Simulation Parameters I = 2.5x1018 W/cm-2, W =12.5 mm 512 cells 100 mm 512 cells 100 mm Plasma Background ne = 2x1019 cm-3 2340 cells 56.18 mm Simulation ran for 6400 hours on DAWSON (~4 Rayleigh lengths) –Laser: • a0 = 1.1 • W0=15.6 12.5mm • l/p = 10 –Particles • 2x1x1 particles/cell • 500 million total –Plasma length • L=.2cm • 50,000 timesteps Simulations: no fitting parameters! Nature papers, agreement with experiment 3D Simulations for: Nature V431, 541 (S.P.D Mangles et al) Imperial Data #( /((dE/E) ) 3D OSIRIS 12 1.4 10 1.2 1012 1 1012 • • In experiments, the # of electrons in the spike is 1.4 108. In our 3D simulations, we estimate of 2.4 108 electrons in the bunch. 8 1011 6 1011 4 1011 2 1011 0 -2 1011 -50 0 50 100 Energy (MeV) 150 200 Movie of Imperial Run Plasma density and laser envelope QuickTime™ and a MPEG-4 Video decompressor are needed to see this picture. 3D PIC simulations: Tweak parameters Propagation: 2 mm Scenario: • self-focusing (intensity increases by 10) • longitudinal compression Excite highly nonlinear wakefield with cavitation: bubble formation • trapping at the Experiment X point • electrons dephase and self-bunch • monoenergetic electrons are behind PIC the laser field Parameters: E=1 J, 30 fs, 18 µm waist, 6×1018 cm-3 Full scale 3D LWFA simulation using OSIRIS Predict the future: 200TW, 40fs State-of- the- art ultrashort laser pulse 0 = 800 nm, t = 30 fs •Simulation Parameters I = 3.4x1019 W/cm-2, W =19.5 mm 256 cells 80.9 mm 256 cells 80.9 mm Plasma Background ne = 1.5x1018 cm-3 4000 cells 101.9 mm Simulation ran for 75,000 hours on DAWSON (~5 Rayleigh lengths) –Laser: • a0 = 4 • W0=24.4 19.5mm • l/p = 33 –Particles • 2x1x1 particles/cell • 500 million total –Plasma length • L=.7cm • 300,000 timesteps OSIRIS 200 TW simulation: Run on DAWSON Cluster A 1.3 GeV beam! The trapped particles form a beam. • • Beam loading Normalized emittance:The divergence of the beam is about 10mrad. Energy spread: Physical picture Evolution of the nonlinear structure • The blowout radius remains nearly constant as long as the laser intensity doesn’t vary much. Small oscillations due to the slow laser envelope evolution have been observed. QuickTime™ and a MPEG-4 Video decompressor are needed to see this picture. • Beam loading eventually shuts down the self injection. • The laser energy is depleted as the accelerating bunch dephases. The laser can be chosen long enough so that the pump depletion length is longer than the dephasing length. QuickPIC loop: 2-D plasma slab Wake (3-D) Beam (3-D): Laser or particles 1. initialize beam 2. solve 2 , 2 e Fp , 3. push plasma, store 4. step slab and repeat 2. 5. use to giant step beam QuickPIC: Basic concepts Maxell’s equations in Lorentz gauge Full PIC (no approximation) Let : s z, ct z 1 ( 2 c 1 ( 2 c dPe 1 q (E v e B) e dt c plasma e : dXe v e dt dPb 1 q (E v b B) b dt c beam e : dXb v b dt 2 4 2 )A j t 2 c 2 2 2 ) 4 t Assume : (1) s (quasi static approximation) (2) v b c 4 A j c 2 4 2 Let : A// QuickPIC 2 4 4 ( 2 j // c Particle pusher(relativistic) ) dPe qe 1 d( /c) 1 v /c (E c v e B) ez plasma e : dXe v e d( /c) 1 v ez /c dPb 1 q (E v b B) d(s /c) b c beam e : dXb v b d(s /c) Solved by 2D field solver QuickPIC: Code structure QuickTime™ and a TIFF (LZW) decompressor are needed to see this picture. QuickPIC Benchmark: Full PIC vs. Quasi-static PIC Benchmark for different drivers 0.1 Longitudinal Wakefield (mcp/e) Longitudinal Wakefield (mcp/e) 3 Osiris QuickPIC (l=2) QuickPIC (l=4) 2 1 0 -1 -2 e- driver -3 -8 -6 -4 -2 0 2 4 6 Osiris QuickPIC (l=2) 0.05 0 -0.05 -0.1 -10 8 e+ driver -5 0 10 1 2 OSIRIS QuickPIC Longitudinal Wakefield (mcp/e) Longitudinal wakefield(mcp/e) 5 (c/p) (c/p) 1 0 -1 e- driver with ionization -2 Osiris QuickPIC (l=2) 0.5 0 -0.5 -1 -3 -5 0 5 (c/p) 10 laser driver -6 -4 -2 0 2 4 6 Excellent agreement with full PIC code. More than 100 times timesavings. Successfully modeled current experiments. Explore possible designs for future experiments. Guide development on theory. (c/p) 100+ CPU savings with “no” loss in accuracy A Plasma Afterburner (Energy Doubler) Could be Demonstrated at SLAC 0-50GeV in 3 km 50-100GeV in 10 m! 3 km 30 m Afterburners S. Lee et al., Phys. Rev. STAB, 2001 Excellent agreement between simulation and experiment of a 28.5 GeV positron beam which has passed through a 1.4 m PWFA OSIRIS Simulation Prediction: Experimental Measurement: OSIRIS Head Peak Energy Loss 64 MeV 65±10 MeV Peak Energy Gain 78 MeV 79±15 MeV E162 Experiment Tail Head Tail 5x108 e+ in 1 ps bin at +4 ps • Identical parameters to experiment ionization: Agreement is excellent! QuickTime™ and a YUV420 codec decompressor are needed to see this picture. including self- Relative Energy (GeV) Full-scale simulationof E-164xx is possible using a new code QuickPIC +4 +2 0 -2 -4 -5 0 +5 X (mm) Full-scale simulationof E-164xx is possible using a new code QuickPIC QuickTime™ and a YUV420 codec decompressor are needed to see this picture. QuickTime™ and a YUV420 codec decompressor are needed to see this picture. Full-scale simulation of a 1TeV afterburner possible using QuickPIC 5000 instead of 5,000,000 node hours • We use parameters consistent QuickTime™ and a MPEG-4 Video decompressor are needed to see this picture. with the International Linear Collider “design” •We have modeled the beam propagating through ~25 meters of plasma. I see a day where the world is fueled by fusion energy. I see a day when high energy accelerators will fit on a tabletop. I see a day where particle simulations will use 1 trillion particles Wakefield equations: “2D-electro and magneto-statics Maxwell equations in Lorentz gauge 1 ( 2 c 1 ( 2 c Reduced Maxwell equations 4 2 4 2 A j ) A j c 2 t c 2 Quasi-static approx. 4 2 2 2 4 ( j /c) ) 4 z 2 t ( j/c) 2 We define ,A (ct z ,x ), A(,x ) Az j 0 Antonsen and Mora 1997 Whittum 1997 Huang et al., 2005 (QuickPIC) Quasi-static Model including a laser driver Maxwell equations in Lorentz gauge 1 2 4 ( 2 2 )A j 2 quasi - static : s 0 c t c 1 2 2 s z, ct z ( 2 2 ) 4 c t Laser envelope equation: dPb qb c 3D loop begin 2D loop begin Initialize beam Initialize plasma Call 2D routine Field Solver Push beam particles Push plasma particles Deposition Deposition 3D loop end 4 j c 2 4 2 A 2p 2 2 2 2 ik0 a a k0 pa = k0 a s 02 p V E b B ds c dP qe V For plasma electrons : e [E ( e B ) ] d c Ve // c For beam electrons : Reduced Maxwell equations 2D loop end Iteration Pipelining: scaling quasi-static PIC to 10,000+ processors beam 1 Initial plasma slab 2 3 4 Initial plasma slab 1 solve plasma response 2 3 4 solve plasma response solve plasma response solve plasma response solve plasma response update beam update beam update beam update beam update beam beam Without pipelining: Beam is not advanced until entire plasma response is determined With pipelining: Each section is updated when its input is ready, the plasma slab flows in the pipeline. LWFA - Accelerating Field •Isosurface values: 512 cells 40.95 mm •Blue : -0.9 •Cyan: -0.6 •Green: -0.3 •Red: +0.3 •Yellow: +0.6 •Electric Field in normalized units me c p e-1 Simulations The 200 TW run: Dephasing ~ Pump depletion Given a Laser we pick the plasma density and we evaluate from our formulas: w0 20mm 30 fs P 200TW 0.8mm a0 4 n p 1.5 1018 cm3 After 5 Zr / 7.5 mm P 10 Pc Total charge = 1.1 nC f(E) (a.u.) 2.5 f(E) LT 1.0cm Ldp 1.3cm E 1.5GeV 2 1.5 1 0.5 0 800 1200 1600 Energy (MeV) 2000 Physical picture of an “optimal” regime Geometry - fields • The ponderomotive force of the laser pushes the electrons out of the laser’s way. • The particles return on axis after the laser has passed. • The region immediately behind the pulse is void of electrons but full of ions. • The result is a sphere (bubble) moving with the speed of (laser) light, supporting huge accelerating fields. Physical picture Evolution of the nonlinear structure • The front of the laser pulse interacts with the plasma and loses energy. As a result the front etches back. • The shape accelerating change. and size structure of the slightly • Electrons are self-injected in the plasma bubble due to the accelerating and focusing fields. • The trapped electrons make the bubble elongate. PIC Simulations of beam loading in blowout regime: Used the new code QuickPIC (UCLA,USC,U.Maryland) Bi-Gaussian shape sz= 1.2 c/p, nb/np= 26 Wedge shape w/ beam load beam length = 6 c/p, nb/np= 8.4, Ndrive = 3x1010, Ntrailing = 0.5x1010