17th IAEA FUSION ENERGY CONFERENCE, YOKOHAMA, JAPAN THEORY SUMMARY

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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 Pasteurs
QuadrantProf. Donald Stokes, Dean, Princeton
Woodrow Wilson School
Considerations of Use? No
Yes
Bohr
Pasteur
Quest for Basic Understanding? No
Yes
Edison
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 wavesinteract?
• 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
atomic mfp
electron-ion mfp
system size
skin depth
tearing length
Huge range of spatial and temporal scales
Overlap in scales often means strong (simplified)
ordering not possible
ion gyroradius
debye length
electron gyroradius
Spatial Scales (m)
10-6
10-2
10-4
100
102
pulse length
current diffusion
Inverse ion plasma frequency
inverse electron plasma frequency
confinement
ion gyroperiod
Ion collision
electron gyroperiod
electron collision
10-10
10-5
100
105
Temporal Scales (s)
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Scientific ComputingCritical to Discovery in
Many Scientific Disciplines
Combustion
Materials
DOE Science Programs Need Dramatic Advances in
Simulation Capabilities To Meet Their Mission
Goals
Global Systems
Health Effects, Bioremediation
Subsurface Transport
Fusion Energy
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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 DOEs 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-Disciplin
ary 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-space
• Scalability 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
Problem with Mathematical Model?
Theory (Mathematical Model)
Computer Science (System Software)
Applied Mathematics (Basic Algorithms)
Computational Science (Scientific Codes)
Problem with Computational Method?
Computational Predictions
Inadequate
Yes
Agree w/ Experiments?
No
Speed/Efficiency?
Use the New Tool for Scientific Discovery (Repeat
cycle as new phenomena encountered )
Comparisons empirical trends sensitivity
studies integrated measurements (spectra,
correlation functions, heating rates )
Adequate
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MACROSCOPIC (MHD) SIMULATIONS
DIFFERENT
LEVELS OF ANALYSIS CAPABILITY PPPL, SAIC, MIT,
LANL, NYU, GA, U.Wisc., U. Texas, U. Colorado
Less complex model, valid for high-collisionality,
strong fields, long times
More computationally demanding. Required to
describe many important but subtle phenomena.
Two Fluid MHD plus energetic gyro-particles
Gyro-particle ions and fluid electrons
Full orbit particle ions and fluid electrons
Single Fluid Resistive MHD
Two Fluid MHD (electrons and ions)
MHD modes destabilized by wave-particle resonance
with energetic species
External kink modes
Neoclassical tearing mode (including rotation)
Collisionless reconnection
Tilting and interchange modes in FRC
Kinetic stabilizationof internal MHD modes by ions
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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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MHD SIMULATION OF INTERNAL RECONNECTION EVENT
UNSTABLE INTERNAL KINK (LEFT) EVOLVES (RIGHT)
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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, MITMission Research,
Lodestar, CompXImproved 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
  MPPs

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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 100s 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 _at_ 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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3D Gyrokinetic Toroidal Code (GTC) Scalable on
Massively Parallel Computers
100
IBM SP
10
computing power
1
CRAY T3E
0.1
0.01
10000
1000
1
100
10
number of processors
Y-axis number of particles (in millions) which
move one step in one second
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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-Mod Tokamak interpreted with MPP
neutrals code (DEGAS 2) GPI results compared
vs. 3D EM fluid code local (flux tube)
simulations of plasma 0.5 cm outside separatrix
normalized to same total amplitude
Fluctuation amplitude
Simulation
GPI Images
k (cm-1)
Initial k-spectrum Comparisons
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New Cross-Disciplinary Opportunities for
Diagnosing and Understanding Turbulence
Break-up and scattering of microwaves from plasma
turbulence
Target plasma
Growth of Radial structures
Zonal flows and decorrelation
Z. Lin, GTC Simulation G.J. Kramer, E. Valeo, R.
Nazikian, Full Wave Simulation of m-wave
Reflection S. Klasky, I. Zatz, Visualization
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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
  SimulationsU. 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

Flame-vortex interactions
Compressed turbulence
Laser-driven shock instabilities
Nova outbursts on white dwarfs
Richtmyer-Meshkov instability
Cellular detonations
Helium burning on neutron stars
Rayleigh-Taylor instability
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Relation to other scientific disciplines

• Space Physics
• reconnection in Earths 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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Simulation of Two-Stream Instability
Heavy Ion Fusion Virtual National Laboratory LBL,
LLL, PPL

• Dipole surface mode can be destabilized with
  introduction of background electron component
  BEST Code 3D PIC for ions and electrons

t0
t200

• 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

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3-D Magnetic Reconnection and Anomalous
ResistivityU. Maryland, Max Planck, Dartmouth

• Particle simulations with 70 M particles and 20 M
  grid points
• Development of turbulence in 3-D model
• two-stream instabilities
• anomalous resistivity

Zeiler, Swisdak, et al. GM1.003
Drake, et al., GM1.007
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Generation of Electron Holes(possible
relevance to satellite observations)
z
Ez

• Intense electron beam generates two-stream
  instability
• nonlinear evolution into electron holes
• localized regions of intense anti-parallel
  electric field
• strong electron scattering

x
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Driving Applications
Princeton Universitys PICASso Program
Bio
PPPL
Genomics
Astrophysics
Biology, Genomics
CS
Astro
Finance
Geo
Eng.
GFDL
Science/Engineering
Geosciences
Plasma Physics
Program in Integrative Computer and Application
Sciences
The Computational Pipeline
Internet Services
Models
Methods
Software
Networks and Distributed Systems
Scalable Systems
DataManagement
Visualization
Mobile Services
Scalable Services
Integrative Research and Training in Entire
Computational Pipeline
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.