Current status theory and simulations ALEGRO WG3 J. Vieira web.ist.utl.pt/ jorge.vieira � epp .tecnico.ulisboa.pt || golp.tecnico.ulisboa.pt � � � GoLP / Instituto de Plasmas e Fusão Nuclear Instituto Superior Técnico, Lisbon Portugal Courtesy W. An et al. golp golp INSTITUTO DE PLASMAS E FUSÃO NUCLEAR Jorge Vieira | ALEGRO workshop, Oxford | March 26, 2018
Acknowledgements Contributions from H. Vicenti (CEA) , T. Mehrling, (LBNL); R.A. Fonseca (ISCTE, IST), J. England (SLAC) ; U. Niedermayer (TUD) , B. Cowan (TECH-X), W. An (UCLA), D. Gordon (NRL) ) Jorge Vieira | ALEGRO workshop, Oxford | March 26, 2018
Physics Models for Plasma Based Collider Simulation D. Gordon et al. Desired conditions at final focus determine the physics issues: • Enough high energy events per second to measure something – TeV energy: long plasmas, high peak power lasers – Average power: long time scale behavior (hydro/transport) – Emittance: source emittance, emittance growth • Ability to generate/manipulate short positron bunches – Novel wakefield structures – Perturbative or nonlinear QED processes • Polarization resolution is important to physics case – Question of polarized sources and polarization preservation 25/03/18 1 Ricardo Fonseca | ALEGRO 2018
Physics Models for Plasma Based Collider Simulation D. Gordon et al. Reasonable guess at major and ancillary components points to physics: Propagation coupled to Laser Polarization Spin-resolved dynamics: rate equations; Module Dirac Equation Preservation Flow models (cooling); BMT Equation Material damage. Injection Acceleration Final Focus Stage Stages Beamstrahlung Usual Maxwell- Lorentz; Beam Emittance Growth Coupling Sources Plasma Chemical kinetics Elements Hydrodynamics & Sources Ionization physics, Transport QED models, Plasma lenses, MHD, Cathode models material damage. Ricardo Fonseca | ALEGRO 2018
State-of-the-art of current modeling tools for Laser/Plasma Wakefield Accelera;on Require kine>c I. Context III. Methods for realis;c ;me/ressource-to-solu;on « Par>cle-In-Cell (PIC) » driver : simula>ons Reduce LWFA Reduce ;me/length Mi;gate numerical dimensionality scale dispari;es ar;facts R-Z geometry Quasi-sta>c/ Dispersion-free Wavebreaking • PWFA With Azimuthal Envelope driver : Maxwell solvers Non-linear regimes • decomposi>on Adapta>ve Mesh Lorentz invariant Refinement par>cle pushers Laser envelope II. Challenges to overcome in LWFA/PWFA simula;ons Boosted frame Galilean solvers/ « 3D standard full PIC modelling is extremely challenging » Fluid Bumped dispersion Merging/SpliSng 3D geometry very costly • >10 9 macropar;cles/10 9 cells Driver 1 µm / Large ;me/length scale • IV. Methods to account for physics beyond Vlasov Acc length cm to 100 m dispari;es Field/collisional ioniza>on QED Monte-Carlo modules • • High spa;o-temporal Numerical ar;facts • Radia>on (sub-cell) Spin polariza>on • • resolu;on required H. Vincen;*, T. Mehrling* and J-L Vay (with contribu;ons from: R. Lehe, C. BenedeL, X. Davoine, W. Ann, T. Grismayer, M. Vranic and K. Lotov) - *speakers Ricardo Fonseca | ALEGRO 2018
Algorithmic needs for LWFA: quasi-static PIC algorithm QuickPIC QuickPIC QuickPIC is a 3D parallel Quasi-Static PIC code, which is developed based on the framework UPIC. https://github.com/UCLA-Plasma-Simulation-Group/QuickPIC-OpenSource Recent Progress MPI+OpenMP with Tiles OO Design Using Fortran 2003 Open Source on Github Vectorization on KNL QuickPIC simulation of (3.61 ns/particle/step) QuickPIC simulation of two-bunch positron-driven PWFA. electron-driven PWFA experiment at FACET shown on the Nature Future Plans cover. Adaptive 2d and 3d time steps Dynamic load balancing Adaptive mesh refinement Adaptive particle loading QuickPIC simulation of LWFA with a beam load W. An et al. http://picksc.idre.ucla.edu Ricardo Fonseca | ALEGRO 2018
Towards Exascale Computations R. A. Fonseca et al. • Outstanding progress in computational power since 1950s • Present systems can reach performances of 0.1 EFlop/s Dynamic load balancing of a LWFA simulation • Energy cost for calculations has gone down by 14 orders of magnitude • Continuous evolution of architectures and computing paradigms � • Exascale simulations are within reach • Present simulations can already track > 10 13 particles for millions of time steps • Increasing quality and quantitative fidelity of simulations • Continuously evolve algorithms and codes to e ffj ciently use new generations of computing hardware � • Community e fg ort among experts in large scale plasma simulation • This evolution presents a formidable challenge for Derouillat et al, CPC 222 351 computational physicists (2018) • Useful to have an ecosystem of codes where ideas are shared. • The community needs sustainable support for exascale software development 7 Ricardo Fonseca | ALEGRO 2018
WG7 (DLA): Optical System Design Combining Analytical Calculation, FDTD, AVM, and NLSE J. England et al. couplers splitters phase shifters T. Hughes, et al. “On-Chip Laser Power Delivery System for Dielectric • Design Study of Integrated Multi-Stage DLA Network Laser Accelerators,” submitted (2018) • Realistic Component Parameters • Adjoint Variable (AVM or “Inverse Design”) Based Structure Optimizations Ricardo Fonseca | ALEGRO 2018
WG7 (DLA): Particle Tracking Using Semi- Analytic 6D DLA Tracker U. Niedermayer et al. Phys. Rev. Accel. Beams 20 , 111302 (2017) One kick per grating cell Kicks by resonant Fourier coefficient (one complex number per grating cell) (numerically lightweight) Transverse kick by Panofsky-Wenzel theorem Symplectic code Can be applied to laterally coupled structures à No artificial emittance increase Subrelativistic & Relativistic structures Tilted grating structures à Natural emittance increase Alternating phase / Spatial Harmonic focusing properly determined J. England et al. Ricardo Fonseca | ALEGRO 2018
Key computational question for DLA collider • Will beam remain stable over km of propagation? • Or are beam-driven wakefields a show-stopper? • Need algorithms/codes for propagation with wakefields • Wakefields for short (~1 mm–1 cm) structures can be computed with standard PIC (mostly—see below) • But even meter scale (~million structure periods) intractable • Need reduced model for wakefields to propagate with tracking • Wakefield physics not even fully understood • Optical bunches have frequency content deep in UV • What is material response? Need iteration between fundamental modeling and experiment B. Cowan et al. Ricardo Fonseca | ALEGRO 2018
Conclusions Plasma based acceleration Full PIC codes are the most predictive but are very CPU expensive but . Reduced codes are less accurate. Combination and cross check between different models is crucial. Large efforts devoted to improving the accuracy of the algorithms (e.g. accurate predictions of beam emittance growth requires numerical Cherenkov free solvers). Improving agreement with experiments/understanding the origin of disagreements is critical to improve current designs and requires combined efforts of numerical simulations, theory and experimental diagnostics (e.g. effects of higher order laser modes/accurate description of laser profiles in simulations). Including additional physics beyond electromagnetism is important to tackle open questions (spin tracking, ionisation, disruption, hydro codes, …). Investigating new types of plasma waves (with different topologies, geometries) required to address current challenges (e.g. positron acceleration) and to open new avenues of research DLA Current challenge: staging several accelerating structures is critical to boost energy gains Accurate and systematic numerical modelling of 3D beam dynamics is an on-going effort Jorge Vieira | ALEGRO workshop, Oxford | March 26, 2018
Agenda Jorge Vieira | ALEGRO workshop, Oxford | March 26, 2018
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