W.B.Mori UCLA Orion Center: Computer Simulation. Simulation component of the ORION Center Just as...
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Transcript of W.B.Mori UCLA Orion Center: Computer Simulation. Simulation component of the ORION Center Just as...
W.B.Mori UCLA
Orion Center: Computer Simulation
Simulation component of the ORION Center
Just as the ORION facility is a resource for the ORION Center, codes such as OSIRIS and quickPIC will be a resource for modeling experiments.
This will be accomplished by encouraging collaborative partnerships.
The proposed simulation research in within the ORION Center includes:
Developing high fidelity parallelized software: currently OSIRIS, quickPIC, and UPIC
Model the full-scale of current and planned experiments ~50MeV -1GeV
Lay the foundation for enabling full-scale modeling of 100+ GeV plasma-based colliders
Real-time feedback between experiment and simulation
A new paradigm of scientific research
Close coupling between experiment and full-scale, three-dimensional, high-fidelity particle based simulations
Refraction of an Electron Beam:Interplay Between Simulation & Experiment
Laser off Laser on
3-D OSIRIS
PIC Simulation
Experiment(Cherenkov
images)
1 to 1 modeling of meter-scale experiment in 3-D!
P. Muggli et al., Nature 411, 2001
One goal is to build a virtual accelerator:A 100 GeV-on-100 GeV e-e+ Collider
Based on Plasma Afterburners
Afterburners
3 km
30 m
Beam-driven wake* Fully Explicitz .05 c/p
y, x .05 c/p
t .02 c/p
# grids in z 350
# grids in x, y 150# steps 2 x 105
Nparticles ~.25-1. x 108 (3D)
Particles x steps ~.5 x 1013 (3D) - ~ 5,000 hrson SP3
Computational challenges for modeling plasma wakefield acceleration
(1 GeV Stage)
Parallel Full PIC OSIRIS UPIC
Parallel quasi-static PIC quickPIC
Other codes exist within the community, e.g.,
OOPIC/Vorpal
The parallel simulation facility of the center includes:
Modeling Plasma Wakefield Acceleration Modeling Plasma Wakefield Acceleration requires particle based modelsrequires particle based models
• Space charge of drive beam displaces plasma electrons
• Transformer ratio
• Wake Phase Velocity = Beam Velocity (like wake on a boat)
• Plasma ions exert restoring force => Space charge oscillations
E Ez acc dec beam. .
• Wake amplitude N b z 2 ( )fornz p
o2
1
++++++++++++++ ++++++++++++++++
----- --- ----------------
--------------
--------- ----
--- -------------------- - --
---- - -- ---
------ -
- -- ---- - - - - - ------ - -
- - - - --- --
- -- - - - - -
---- - ----
------
electron beam
+ + + + + + + + + + ++ + + + + + + + + + + + + + ++ + + + + + + + + + + + + + +
+ + + + + + + + + + + + + + +-
- --
--- --
EzEz
• Maxwell’s equations for field solver
• Lorentz force updates particle’s position and momentum
Interpolate to particles
Particle positions
Lorentz Force
push
partic
les weight to grid
z vi i,
n m n mj, ,,
dpdt
E v B c
E Bn m n m, ,,
t
Computational cycle (at each step in time)
What Is a Fully Explicit Particle-in-cell Code?
Typical simulation parameters:~107-109 particles ~1-100 Gbytes~104 time steps ~102-104 cpu hours
OSIRIS.frameworkBasic algorithms are mature and well tested
• Fully relativistic
• Choice of charge-conserving current deposition algorithms
• Boris pusher for particles, finite field solver for fields
• 2D cartesian, 2D cylindrical and 3D cartesian
• Field and impact ionization models
• Arbitrary particle initialization and external fields
• Conducting and Lindman boundaries for fields; absorbing, reflective, and thermal bath for particles; periodic for both
• Moving window
• Launch EM waves: field initialization and/or antennas
• Launch particle beam
• particle sorting and ion subcycling
• Extended diagnostics using HDF file output:–Envelope and boxcar averaging for grid quantities–Energy diagnostics for EM fields–Phase space, energy, and accelerated particle selection diagnostics for particles
UCLA
Effort was made to improve speed while maintaining parallel efficiency:
2D 128x128 with 16 particles/cell per processor and Vth=.1c
CPU#
Speed
s/ps
Push
%
BCpart BCcurr Field
Solve
BC Field
other Efficiency
1 2.1 95 4.2 .03 .56 .03 .19 100
4 2.13 95 3.89 .09 .59 .1 .31 99.48
16 2.2 92.8 4.91 .53 .71 .38 .68 95.82
64 2.3 89.3 6.87 1.28 .57 1.09 1.09 91.82
256 2.29 88.7 6.97 1.29 .55 1.39 1.15 92.16
512 2.37 85.2 7.42 1.27 .54 1.87 3.72 88.52
1024 2.29 90 5.6 1.1 .56 1.3 1.4 92.1
Speed in 3D: 3.2s/ps with 80%efficiency on 512 processors and 60% on 1024 processors(323 cells and 8 particles/cell/processor)
quickPIC• Quasi-static approximation: driver evolves on a much
longer distances than wake wavelength· Frozen wakefield over time scale of the bunch length
·
· => and/or xR >> z (very good approximation!)
Beam
Wake
UCLA
Basic equations for approximate QuickPIC
• Quasi-static or frozen field approximation converts Maxwell’s equations into electrostatic equations
(1
c2
2
t2 2 )A 4
cj
(1
c2
2
t2 2 ) 4
2 A 4
cj
2 4
Maxwell equations in Lorentz gauge Reduced Maxwell equations
j jb je jb cbˆ z • )ˆ( // zAA
Local-- at any z-slice depend only on j at that slice!
, A , A(z ct )
Quasi-static approx.
• A//
Forces :
plasma : Fe e
beam : Fb e
2-D plasma slab
Beam (3-D)Wake (3-D)
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 loop (based on UPIC):
Parallelization of QuickPIC
zy
x
Node 3 Node 2 Node 1 Node 0
x
y
Node 3
Node 2
Node 1
Node 0
Benchmarking
Full PIC: OSIRIS and OOPIC
Full PIC vs. quasi-static PIC: OSIRIS and quickPIC
PIC against experiment: OSIRIS and quickPIC against E-157/E-162
quickPIC vs. OSIRIS
Positron driver
-0.08
-0.06
-0.04
-0.02
0
0.02
0.04
0.06
0.08
-10 -5 0 5 10
OsirisStandard QuickPICFull QuickPIC
(c/p)
-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
-3 -2 -1 0 1 2 3
Full QuickPICStandard QuickPICOsiris
(c/p)
Lon
gitu
dina
l Wak
efie
ld (
mc
p/e)
Focu
sing
Fie
ld (
mc
p/e)
Plasma density = 2.1E14 cm-3, Beam Charge = 1.8E10 e+
Head Tail
Wakefield and focusing field from QuickPIC agree well with those from OSIRIS, and it is >100 times faster!
Full-scale modeling of experiments:A new paradigm of research
Plasma wakefield accelerator(PWFA) E-157/E-162electron acceleration/focusingpositron acceleration/focusing
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:
Peak Energy Loss64 MeV
65±10 MeV
Peak Energy Gain78 MeV
79±15 MeV
5x108 e+ in 1 ps bin at +4 ps
Head Tail Head Tail
OSIRIS E162 Experiment
Beyond planned experiments:Afterburner modeling
Nonlinear wakespreformedself-ionized
Nonliear beamloadingStability: hosingFinal focusing
OOPIC shows that a PWFA e- driver can ionize neutral Li
• OOPIC simulations show that tunneling ionization plays a key role in the PWFA afterburner concept– The self-fields of the bunch can ionize Li or Cs– High particle density (i.e. large self-fields) is required to drive a strong wake
• In Li, a shorter afterburner drive beam could ionize the plasma by itself– This approach would greatly simplify beam-driven wakefield accelerators– r=20 m; z=30 m; 2x1010 e- in the bunch; E0=11.4 GV/m
• We need to model evolution of the drive beam with TI effects included
Superposition cannot be used for nonlinear beamloading: 1+1 ≠ 2
2nd beam charge density
1st beam charge density
Linear superposition
Nonlinear wake
Nonlinear wake
Hosing can be studied for afterburner
parameters using quickPIC
Electron drive beam hoses as it propagate over a long distance in the plasma
3D image of the plasma charge density under blow-out regime
t = 0 t = 64,800 (1/p)
++ ++ ++ ++ ++ ++ + ++ + ++ ++ ++ ++ ++ ++ ++
-- -- -- - ---- -- --- ---- ----
- - -- - - - ---Er --
---------- --- --- - - - -- - -- -- -----------
-
----------
-- --- --
-- ---------- --- - ---
----- ----
-- ------
- - - --- - --
-- - ---
++++++++++++++++++++++++++ +++++++++++++++ +++++++++++++++
-
---
-- ---
EzEz
Focusing fieldAcceleration field
Simulations are a key piece of the ORION Center
Mature fully parallelized codes are a “facility” for the Center.
Codes have been benchmarked against each other and experiment.
One goal is to provide realtime feedback between experiment and theory.
Another goal is to lay the foundation for pushing advanced accelerators forward.
Role for this workshop:To discuss the simulation needs for new ideas: Can they be done with existing software?What new physics modules are needed?Applying methods in UPIC and OSIRIS.framework to LEAP and Sources.