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ADVANCED COMPUTATION IN PLASMA PHYSICS
Forty-Third American Physical Society
Division of Plasma Physics Annual Meeting
Long Beach, California
W. M. TANG
Princeton University, Plasma Physics Laboratory,
2 November 2001
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PERSPECTIVE
• GOAL: Reliable predictions of complex properties of high temperature plasmas– Acquire scientific understanding needed for predictive models
superior to empirical scaling
• Plasma Science is both utilizing and contributing to the exciting advances in Information Technology and Scientific Computing.
• Advanced computation in tandem with theory and experiment is powerful new tool for scientific understanding and innovation in research
• Focus of present talk: Magnetically-Confined Plasmas (Fusion Energy Sciences )
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Fusion Plasma Science is in Pasteur’s QuadrantProf. Donald Stokes, Dean, Princeton Woodrow Wilson School
Considerations of Use?
No – Yes
Qu
est
for
Bas
icU
nd
erst
and
ing
?
No
–
Yes
Bohr
Edison
Pasteur
Tight coupling of understanding and innovation.
Strong commitment to both!
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Plasma Science ChallengesNRC Plasma Science Committee
• Macroscopic Stability– What limits the pressure in plasmas?
• Astrophysical accretion disks
• Wave-particle Interactions– How do particles and plasma waves
interact?• Solar coronal heating
• Microturbulence & Transport– What causes plasma transport?
• Accelerator collective dynamics
• Plasma-material Interactions– How can high-temperature plasma
and material surfaces co-exist?• Materials processing
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Challenge to Theory & Simulations
• Huge range of spatial and temporal scales
• Overlap in scales often means strong (simplified) ordering not possible
10-6 10-4 10-2 100 102
Spatial Scales (m)electron gyroradius
debye length
ion gyroradius
tearing length
skin depth system size
atomic mfp electron-ion mfp
10-10 10-5 100 105
Temporal Scales (s)
electron gyroperiod electron collision
ion gyroperiod Ion collision
inverse electron plasma frequency confinement
Inverse ion plasma frequency current diffusion
pulse length
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Scientific ComputingCritical to Discovery in Many Scientific Disciplines
Subsurface Transport
GlobalSystems
DOE Science ProgramsNeed Dramatic Advances
in Simulation Capabilities
To Meet TheirMission Goals
Health Effects, Bioremediation
Fusion Energy
CombustionMaterials
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Plasma Physics in DOE Advanced Scientific Computing Programs
• New DOE Office of Science Program: “Scientific Discovery through Advanced Computing” ---- FES is an active member of this broader scientific portfolio with access to new resources
• Plasma Science Advanced Computing Institute (PSACI)– Lead role for coordinating Plasma Science component of
DOE’s new SciDAC Program
– Peer-reviewed projects include FES Collaboratory, Magnetic Reconnection, Wave Heating, Atomic Physics, Turbulent Transport, and MHD Simulations
– Program Advisory Committee (with distinguished members from outside & within FES) provides excellent advice/guidance
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COMPUTATIONAL CHALLENGES IN FUSION ENERGY SCIENCES IMPORTANT FOR MOST AREAS
(Cross-Disciplinary Opportunities)______________________________________________________________
• Enhance physics models & develop more efficient algorithms to better address scientific issues
Multi-scale physics e.g. Kinetic (electromagnetic) dynamics
Improved algorithms e.g. Adaptive mesh refinement for higher dimensionality
phase-spaceScalability of codes
e.g. Efficient implementation of codes on most powerful MPP supercomputers
• Improve analysis/interpretation of greatly increased volume of simulation data New diagnostic & visualization tools, improved data
management/analysis
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Advanced Scientific Codes --- a measure of the state of
understanding of natural and engineered systems
Theory(Mathematical Model)
AppliedMathematics(Basic Algorithms)
ComputationalScience
(Scientific Codes)
ComputerScience
(System Software)
Problem with Mathematical Model?
Pro
ble
m w
i th
Com
put
ati o
n al
Me t
h od ?
Computational Predictions
Agree* w/ Experiments?
No Yes Speed/Efficiency?
Inadequate
AdequateUse the New Tool for Scientific Discovery
(Repeat cycle as new phenomena encountered )
*Comparisons: empirical trends; sensitivity studies; integrated measurements (spectra, correlation functions, heating rates …)
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Single Fluid
Resistive MHD
Two Fluid MHD
(electrons and ions)
Two Fluid MHD plus energetic
gyro-particles
Gyro-particle ions and
fluid electrons
Full orbit particle ions and
fluid electrons
Less complex model, valid for high-collisionality, strong fields, long times
More computationally demanding. Required to describe many important
but subtle phenomena.
External kink modes
Neoclassical tearing mode (including rotation)
Collisionless reconnection
MHD modes destabilized by wave-particle resonance with energetic species
Kinetic stabilizationof internal MHD modes by ions
Tilting and interchange modes in FRC
MACROSCOPIC (MHD) SIMULATIONS: DIFFERENT LEVELS OF ANALYSIS CAPABILITY
PPPL, SAIC, MIT, LANL, NYU, GA, U.Wisc., U. Texas, U. Colorado
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Neoclassical Tearing Mode (NTM) Analysis Capability
• Self-consistent closure for Neo-classical Fluid Eq.’s being developed & applied [e.g., NIMROD]
• Results to be cross-benchmarked & validated against experimental results
• Enable assessment of NTM impact on beta limit for long-pulse, high-performance tokamaks
•
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• UNSTABLE INTERNAL KINK (LEFT) EVOLVES (RIGHT)
MHD SIMULATION OF INTERNAL RECONNECTION EVENT
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Hot Inner Region Interchanges with Colder Outer Region via Magnetic Reconnection
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MPP Supercomputers Provide Access to New Plasma Wave PhysicsORNL, PPPL, MIT
Mission Research, Lodestar, CompX
Improved Physics and All Orders Spectral Algorithm (AORSA-2D)
• Field solutions for conversion of fast ion cyclotron waves to ion Bernstein waves in 2D for a tokamak – collaboration with Computer Science and Math division at ORNL
• Contours of wave electric field strength for mode conversion using DIII-D tokamak parameters
• Patterns shown here are not revealed in a 1D treatment
• Extension to shorter wavelength and to 3D will be possible with new generation computers
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UNDERSTANDING TURBULENT PLASMA TRANSPORT
An important problem: -- Size of plasma ignition experiment determined by fusion self-heating versus turbulent transport losses-- Dynamics also of interest to other fields (e.g., astrophysical accretion disks)
A scientific Grand Challenge problem A true terascale computational problem for MPP’s
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PLASMA MICROTURBULENCE SIMULATION CODES HAVE MADE EXCELLENT PROGRESS
LLNL, PPPL, GA, U. Maryland, UCLA, U. Colorado • Builds on National Turbulent
Transport Project -- multi-institutional “Grand Challenge”
• Realistic Geometry– Full Torus (3D)– Flux Tube Codes
• Efficient Algorithms– Gyrokinetic --- PIC– Gyrokinetic --- Vlasov
Continuum
• Demonstrated scaling beyond 100’s of processors
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Full Torus Simulations of Turbulent Transport Scaling
• Large-scale full torus gyrokinetic particle simulations for device-size scans• Global field-aligned mesh saves factor ~100 in computation• Efficient utilization of new 5 TF IBM SP @ NERSC (just available 8/01) -- fastest non-classified supercomputer in world• Most recent simulations used 1 billion particles (GC), 125 M spatial grid points, and 7000 time steps --- leading to important (previously inaccessible) new results
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Full Torus Simulations of Turbulent Transport Scaling
• Transport driven by microscopic scale fluctuations (ITG modes) in present devices can change character: transition from Bohm-like scaling ~ (ivi ) to Larmor-orbit-dependent “Gyro-Bohm” scaling ~ (ivi )(I/ a)
• “Rollover” is good news ! (since simple extrapolation is pessimistic)
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0.01
0.1
1
10
100
1 10 100 1000 10000number of processors
com
putin
g po
wer
IBM SP
CRAY T3E
3D Gyrokinetic Toroidal Code (GTC)
Scalable on Massively Parallel Computers
Y-axis: number of particles (in millions) which move one step in one second
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0.1
1
10
1 10
Plasma Edge Turbulence Studies: Experiment and Simulation Comparisons
• S. Zweben & J. Terry et al. + B. Rogers & K. Hallatschek, et al. + D. Stotler(Paper UI1.004)
• Gas Puff Imaging (GPI) Experiments on Alcator C-ModTokamak interpreted with
MPP neutrals code (DEGAS 2)
•GPI results compared vs. 3D EM fluid codelocal (flux tube) simulations of plasma 0.5 cm outside separatrix
k (cm-1)
Flu
ctua
tion
ampl
itude
Simulation
GPI Images
normalized to same total amplitude
Initial k-spectrumComparisons
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New Cross-Disciplinary Opportunities for Diagnosing and Understanding Turbulence
Z. Lin, GTC SimulationG.J. Kramer, E. Valeo, R. Nazikian, Full Wave Simulation of -wave ReflectionS. Klasky, I. Zatz, Visualization
Target plasma Growth of Radial structures Zonal flows and decorrelation
Break-up and scattering of microwaves from plasma turbulence
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THE NATIONAL FUSION ENERGY SCIENCES COLLABORATORY
(involves 40 US sites in 37 states)• Collaboratory Goals:
-- enable more efficient use of experimental facilities by developing more powerful between pulse data analysis
-- enable better access by researchers to analysis & simulation codes, data, and visualization tools
-- create standard tool set for remote data access, security, and visualization
• Collaboratory Partners: D. Schissel, et al. :
-- 3 large fusion experiments*
* C-MOD, DIII-D, NSTX
-- 4 computer science centers **
** ANL, LBNL, Princeton U., U. of Utah
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STELLARATOR DESIGN STUDIES
• Optimization of Stability, Transport, and Constructability for Designing National Compact Stellarator Experiment (NCSX)
• Utilization of MPP Computations Essential for Optimizations
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�Collaboration on Magnetic Reconnection Simulations
U. Iowa, U. Chicago, U. Texas FLASH CODE: R. Rosner, et al., U. Chicago
• Solves fully compressible Navier Stokes Equations
(explicit viscosity, implicit dissipation, single-fluid
MHD)
• Fully parallel and uses Adaptive Mesh Refinement
• Supercomputing 2000/Gordon Bell Prize winner
• Large and diverse scope of applications
Cellular detonations
Compressed turbulence
Helium burning on neutron stars
Richtmyer-Meshkov instability
Laser-driven shock instabilitiesNova outbursts on white dwarfs
Rayleigh-Taylor instability
Flame-vortex interactions
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Relation to other scientific disciplines
• Space Physics
– reconnection in Earth’s magnetosphere, solar corona,
astrophysical plasmas
– dynamos, collective phenomena, …….
• High Energy Physics– Collective dynamics impacting advanced accelerator design
• Industrial Applications– Plasma Processing, Xerography, Flat Panel Display, ….
• Computational Physics -- issues common to many areas– advances in solving partial differential equations in complex geometry,
– adaptive mesh refinement in 3D,
– parallel methods for inverting sparse matrices
– etc.
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• Dipole “surface mode” can be destabilized with introduction of background electron component [BEST Code : 3D PIC for ions and electrons]
•Electron-Proton Two-Stream Instability Growing from Initial Noise•Two-stream instability can be stabilized by a modest axial momentum spread. [unwanted electrons in LANL Proton Storage Ring and the Spallation Neutron Source Project]
t=0 t=200
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• Particle simulations with 70 M particles and 20 M grid points
• Development of turbulence in 3-D model– two-stream
instabilities
– anomalous resistivity
3-D Magnetic Reconnection and Anomalous ResistivityU. Maryland, Max Planck, Dartmouth
Zeiler, Swisdak, et al.GM1.003
Drake, et al., GM1.007
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Generation of “Electron Holes”(possible relevance to satellite observations)
• Intense electron beam generates two-stream instability– nonlinear evolution into “electron
holes”• localized regions of intense anti-
parallel electric field
– strong electron scattering
x
z
Ez
f
vz
ions
electrons
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Driving Applications
Sci
ence
/En
gin
eeri
ng
Sca
lab
le S
ervi
ces
Princeton University’s Princeton University’s
PICASso PICASso ProgramProgram
Program in Integrative Computer and Application Sciences
Integrative Research and Training in Entire Computational Pipeline
CS
PPPL
Astro
Geo
Bio
Eng.
GFDL
Genomics
Finance
Models Methods Software
Networksand
DistributedSystems
ScalableSystems
DataManagement Visualization
The Computational PipelineInternet Services
Biology, Genomics
Astrophysics
Plasma PhysicsGeosciences
Mobile Services
Information Archives
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CONCLUSIONS• Advanced Computations is cost-effectively aiding progress
toward gaining the physics knowledge needed to harness fusion energy by making crucial contributions to all areas of Plasma Science.
• Advanced Computations is a natural bridge for fruitful collaborations between Plasma Science and other scientific disciplines.
• Plasma Science is both utilizing and contributing to the exciting advances in Information Technology and Scientific Computing.
• Computational Plasma Science is helping to attract, educate, &
retain young talent essential for the future.