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NERSC 3 Greenbook

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Numerical Tokamak Turbulence Grand Challenge Project

B.I. Cohen, Principal Investigator, Lawrence Livermore National Laboratory
J.M. Dawson, Scientific Leader, Univ. of California at Los Angeles
J.V.W. Reynders, Co-principal Investigator for Infrastructure, Los Alamos National Laboratory
V.K. Decyk, University of California at Los Angeles
W.D. Dorland, University of Texas at Austin
G.W. Hammett, Princeton Plasma Physics Laboratory
G.D. Kerbel, Lawrence Livermore National Laboratory
J.N. Leboeuf, Oak Ridge National Laboratory
W.W. Lee, Princeton Plasma Physics Laboratory
S.E. Parker, University of Colorado, Boulder
R.E. Waltz, General Atomics

Research Objectives: The primary research objective of the Numerical Tokamak Turbulence Project (NTTP) is to develop a predictive ability in modeling turbulent transport due to drift-type instabilities in the core of tokamak fusion experiments through the use of three-dimensional kinetic and fluid simulations and the derivation of reduced models.

Computational Approach: Two classes of three-dimensional initial-value simulation algorithms, gyrokinetic (GK) and gyro-Landau-fluid (GLF), are being applied to the simulation of tokamak turbulent core transport. The GK simulations are based on particle-in-cell (PIC) methods for the self-consistent solution of Poisson's equation (reduced to a quasi-neutrality relation) and plasma equations of motion, and the use of domain decomposition methods to run efficiently in parallel on the T3E and other parallel computers. The GLF algorithm is based on an alternative solution of the fundamental GK and quasi-neutrality equations in which fluid moment equations are solved instead of particle equations. The GLF simulations have been performed on both massively parallel computers and parallel vector computers, particularly the C90 at NERSC. Both flux-tube, i.e., toroidal annulus, and global toroidal GK and GLF simulations are being performed to study tokamak turbulence.

Accomplishments: Because of its relevance to the International Thermonuclear Experimental Reactor (ITER), detailed parameter studies have been conducted with our GK and GLF simulations addressing discharge #81499 in the General Atomics DIII-D tokamak as a base case. Careful comparisons have been made between the results of the GLF and GK simulations of shot 81499 and variants to determine parametric dependences and points of agreement and disagreement between the simulation algorithms (the Cyclone study). Elsewhere GLF and GK simulation results have been compared to experimental findings with good agreement in some cases. As part of the Cyclone study, a GK flux-tube PIC simulation has been the object of a vigorous study of its convergence properties with results so far suggesting that statistical convergence is being obtained. Although the differences between the results for the turbulent ion thermal diffusivity in GK and GLF simulations are not large (GK results are often a factor of 2 to 3 lower than GLF results), the implications of these differences for the projected fusion performance of ITER can be significant. The NTTP simulations have also demonstrated the importance of flow shear and negative central magnetic shear in reducing drift-wave turbulence in tokamaks as observed in experiments. GK simulations have verified the improved confinement in the TEXTOR tokamak due to a small percentage of Ne impurity which has a stabilizing effect on ion-temperature-gradient turbulence. Many NTTP codes have been successfully ported to the T3E in the last year, and a new global GLF code is yielding physics results (c.f., 26 and 27). Progress has been made in including realistic geometrical effects (for example, shaped cross sections and magnetic X-points needed to model plasmas with divertors) and realistic equilibrium plasma profiles in the simulations.

Significance: The NTTP simulations are being used to produce linear and nonlinear calculations of drift-type instabilities in realistic tokamak equilibria, which are leading to a deeper understanding of anomalous transport in current experiments and to improving their performance. This simulation work builds a bridge between theory and experiment, and is providing a basis for reduced transport models intended to fit current experimental databases and from which it is hoped that performance in future experiments can be reliably predicted and optimized. As controlling the energy transport has significant leverage on the performance, size, and cost of fusion experiments like ITER, reliable NTTP simulations can lead to significant cost savings and improved performance in future experiments.

Recent Publications:

Other information at these WWW URLs:


  
Figure 26: Full-cross-section simulation of ion-temperature-gradient-driven turbulence. V. Lynch and J.-N. Leboeuf, ORNL
\begin{figure} \centerline{ \psfig {figure=gb_cohen1.eps,height=160mm,width=160mm,angle=270} }\end{figure}


  
Figure 27: Gyrofluid simulation of ion-temperature-gradient turbulence in a torus mapped onto a DIII-D equilibrium with triangular cross-section. G. Kerbel, LLNL
\begin{figure} \centerline{ \psfig {figure=gb_cohen2.eps,height=160mm,width=160mm,angle=270} }\end{figure}

Summary of Computing Resources Requested by the Numerical Tokamak Grand Challenge

 
Figure 27: Gyrofluid simulation of ion-temperature-gradient turbulence in a torus mapped onto a DIII-D equilibrium with triangular cross-section. G. Kerbel, LLNL
    FY97 FY98 FY99
NERSC T3E T3E node hours (105) 2.5 3.5 4.5
  J-90 node hours (105) 0.04 0.04 0.04
  memory (GB per job) 1-60 1-60 1-60
  disk (TB) 0.2 0.2 0.2
  tertiary storage (TB) 6 6 6
  Onyx hours/yr 200 200 200
ACL Cluster of SMPs node hours (105) 3 7 9
  memory (GB hr per job) 103 2x103 3x103
  disk (TB) 0.3 0.5 1.5
  tertiary storage (TB) 6 6 6
  Onyx hours/yr 200 200 200
Paragons at ORNL processor hours(105) 0.055 0.15 0.3

NERSC 3 Greenbook

next up previous contents
Next: 3D Simulation of Heavy-Ion Up: Fusion Energy Previous: 3d MHD Calculations in
Rick A Kendall
7/13/1998