Hybrid Simulations of Energetic Particledriven

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Hybrid Simulations of Energetic
Particle-driven Instabilities in Toroidal Plasmas
Guo-Yong Fu In collaboration with J. Breslau,
J. Chen, E. Fredrickson, S. Jardin, W. Park,
H.R. Strauss (NYU), L.E. Sugiyama (MIT)
8th IAEA Technical Meeting on Energetic Particles
in Magnetic Confinement Systems 6-8 October 2003,
San Diego, California, USA
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Outline

• Introduction
• M3D code hybrid model, code development
• Examples of M3D Hybrid Simulations
• NBI-driven TAEs in NSTX
• Summary
• Future Work

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Introduction

• We investigate energetic particle-driven MHD
  modes in tokamaks and stellarators by
  particle/MHD hybrid simulations
• Our main tool, M3D, is a 3D global nonlinear
  extended MHD code.
• Our goal is to understand the alpha
  particle-driven MHD instabilities in a burning
  plasma and predict their effects on alpha heating
  and particle loss.
• This talk reports progress towards this goal
  code development, NBI-driven Alfven modes etc.

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Motivation

• In a toroidal plasma (tokama/stellarator),
  energetic particles with velocity comparable to
  Alfven phase speed can resonantly destabilize MHD
  modes such as TAE and CAE, they can also
  induce/excite new modes such as fishbone or
  Energetic Particle Mode(EPM).
• In a magnetic fusion reactor, alpha
  particle-driven MHD modes can results in alpha
  particle loss and change alpha heating profile.
• Key issues of alpha physics are alpha effects on
  sawteeth and alpha particle transport due to
  multiple Alfven modes.

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M3D code
M3D project is part of SciDACs CEMM Center
for Extended MHD Modeling M3D is an extended-MHD
(XMHD) code which has multi-level of
physics Resistive MHD Two fluids Particle/MHD
hybrid
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M3D XMHD Model
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M3D Hybrid Code Development

• extended to general 3D geometry valid for
  stellarators
• massively parallelized via MPI
• benchmarked against NOVA-K code.

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M3D hybrid code has been extended to
unstructured mesh valid for 3D geometry
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M3D hybrid code has been parallelized using
either MPI or OpenMP
512 poloidal planes 7321 mesh points 32 million
particles
1 node 16 processors
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Examples of M3D Hybrid Simulations

• Fishbone instability
• ITER Alpha particle effects on n1 kink
• TAE in stellarators.

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Hot Particle-induced Fishbone Instability
circular tokamak R/a2.76 q(0)0.6,
q(a)2.4 b_total(0) 8 v_h/v_A 1.0,
r_h/a0.05 Isotropic slowing-down hot particle
distribution
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Mode Structure Ideal Kink v.s. Fishbone
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ITER alpha particle effects are not sufficient
to stabilize n1 internal kink mode
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Fast Ion-driven TAE in a Quasi-symmetric
stellarator
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TAE mode structure tokamak v.s. stellarator
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Simulations of Beam-driven Alfven Modes in NSTX

• Recent NSTX experimental observations show rich
  beam-driven instabilities fishbone, TAEs, CAEs
  etc and associated hot particle losses.
• Alfven modes in STs are less understood as
  compared to those in conventional tokamaks.
• Need to study possible new features of
  beam-driven Alfven modes associated with STs
  unique parameter regime low aspect ratio, high
  beta, large energetic ion speed and gyroradius.

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The bursting modes are in the TAE frequency range
(NSTX)
E. Fredrickson

• Multiple modes burst at the same time.
• Toroidal mode number, n, ranges from 2 - 5 with
  the dominant mode being n2 or 3.
• Mode frequencies in reasonable agreement with
  expected TAE frequencies.

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The final mode growth and decayis very fast
E. Fredrickson

• Some of the mode amplitude modulation represents
  "beating" of the multiple modes.
• Mode growth and decay times are approximately 50
  - 100 ms.

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NSTX Parameters and Profiles

• NSTX shot 108530 at t0.267sec
• R87cm, a63cm, B0.43T, ne(0)2.5e13, Ti1.7kev,
  Te1.4kev
• q(0)1.82, q(a)12.9, weakly reversed
• b(0)21, bbeam(0)13
• vbeam/vAlfven 2.1, rbeam/a 0.17

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q profile
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Pressure Profiles Pthermal and Pbeam
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Beam Particle Distribution

• isotropic distribution
• anisotropic distribution.

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The simulation of an NSTX plasma show unstable
TAEs consistent with observations

• NSTX shot 108530 at t0.267sec
• The calculated n2 TAE mode frequency is 73 kHz
  which is close to the experimental value of 70
  kHz (assuming 15kHz toroidal rotation)

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N1, 2 3 Modes in NSTX
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Nonlinear Evolution of n2 TAE Mode Saturation
and Frequency Chirping
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Mode Moving Out After Saturation
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n2 Mode Structure Isotropic v.s. Anisotropic
distribution
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Multiple Mode Simulations (n14)
t180
t220
t270
t139
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Summary

• M3D hybrid code has been extended to general 3D
  geometry and massively parallelized.
• Simulations of NBI-heated NSTX plasmas show
  unstable TAEs with frequencies consistent with
  experimental observations.
• Initial nonlinear simulations show that the n2
  TAE mode moves out radially and its frequency
  chirps down during saturation.

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Future Work

• Simulations of NBI-driven TAE in NSTX for more
  realistic distributions
• Improve M3D for simulations of alpha-driven
  high-n Alfven modes in burning plasmas code
  speed, time step, more physics such as particle
  collision etc.