# Presentation: 490384

##  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**

## 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 *****)**

## Fusion Plasma Science is in Pasteur’s QuadrantProf. Donald Stokes, Dean, Princeton Woodrow Wilson School

**Considerations of Use?**
**No              –             Yes**

**Quest for Basic**
**Understanding?**
**No          –         Yes**

**Bohr**

**Edison**

**Pasteur**

**Tight coupling of understanding and innovation.**
**Strong commitment to *****both!***

## Plasma Science ChallengesNRC 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

## 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

## Scientific ComputingCritical to Discovery in Many Scientific Disciplines

**Scientific Computing*****Critical to Discovery in Many Scientific Disciplines***

**Subsurface Transport**

**Global**
**Systems**

**DOE Science Programs**
**Need Dramatic Advances**
**in Simulation Capabilities**
**To Meet Their**
**Mission Goals**

**Health Effects, Bioremediation**

**Fusion Energy**

**Combustion**

**Materials**

## 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 **

## • Enhance physics models & develop more efficient algorithms to better address scientific issues  

**•**** ****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 ***

## Advanced Scientific Codes ---  a measure of the state of 	     understanding of natural and engineered systems 

**Theory**
- (Mathematical Model)

**Applied**
**Mathematics**
- (Basic Algorithms)

**Computational**
**Science**
- (Scientific Codes)

**Computer**
**Science**
- (System Software)

- Problem with Mathematical Model?

- Problem with Computational Method?

***Computational Predictions***

**Agree* w/ Experiments?**

**No**

**Yes**

**Speed/Efficiency?**

**Inadequate**

**Adequate**

***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 ...)***

## 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**** **

## 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**

## MHD SIMULATION OF INTERNAL RECONNECTION EVENT

- • UNSTABLE INTERNAL KINK (LEFT) EVOLVES (RIGHT)

**MHD SIMULATION OF INTERNAL RECONNECTION EVENT**

## Hot Inner Region Interchanges with Colder Outer Region via Magnetic Reconnection

**Hot Inner Region Interchanges with Colder Outer Region via Magnetic Reconnection**

## Slide 14

## MPP Supercomputers Provide Access to New Plasma Wave PhysicsORNL, 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**

## Slide 16

##      An important problem:  

**     ****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**

## 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**

## Slide 19

## Slide 20

## Full Torus Simulations of Turbulent Transport Scaling

**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

## Full Torus Simulations of Turbulent Transport Scaling

**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)

## 0.01

- 0.1

- 1

- 10

- 100

- 1

- 10

- 100

- 1000

- 10000

- number of processors

- computing power

- 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

## •  S. Zweben & J. Terry et al. + B. Rogers & K. Hallatschek, et al. + D. Stotler

**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

- k (cm-1)

- Fluctuation amplitude

- Simulation

- GPI
- Images

***normalized to same ***
***total amplitude***

**Initial k-spectrum**
**Comparisons**

## Break-up and scattering of microwaves from plasma turbulence 

**Diagnosing and Understanding Turbulence**

***Z. Lin, GTC Simulation***
***G.J. Kramer, E. Valeo, R. Nazikian, Full Wave Simulation of  **********-wave Reflection***
***S. Klasky, I. Zatz, Visualization***

- Target plasma

- Growth of Radial structures

- Zonal flows and decorrelation

- Break-up and scattering of microwaves from plasma turbulence

## Slide 26

## THE NATIONAL FUSION ENERGY SCIENCES COLLABORATORY 

**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

## STELLARATOR DESIGN STUDIES

-  **Optimization of Stability, Transport, and Constructability for Designing National Compact Stellarator Experiment (NCSX) **
** ****Utilization of MPP Computations Essential for Optimizations**

## 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 instabilities***

***Nova outbursts on white dwarfs***

*Rayleigh-Taylor instability*

***Flame-vortex interactions***

## 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.

## Simulation of Two-Stream Instability

**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

**Simulation of Two-Stream Instability**

- t=200

*Heavy Ion Fusion Virtual National Laboratory LBL, LLL, PPL*

## 3-D Magnetic Reconnection and Anomalous ResistivityU. Maryland, Max Planck, Dartmouth

- Development of turbulence in 3-D model
- two-stream instabilities
- anomalous resistivity

**3-D Magnetic Reconnection and Anomalous Resistivity****U. Maryland, Max Planck, Dartmouth**

- Zeiler, Swisdak, et al.
- GM1.003

- Drake, et al.,
- GM1.007

## 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**

**E****z**

## Princeton University’s PICASso Program

***Driving Applications***

**Science/Engineering**

**Scalable Services**

*Princeton University’s **PICASso Program*

**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

- Networks
- and
- Distributed
- Systems

- Scalable
- Systems

- DataManagement

- Visualization

- _The Computational Pipeline_

- Internet Services

- Biology, Genomics

- Astrophysics

- Plasma Physics

- Geosciences

- Mobile Services

- Information Archives

## 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.**** **