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Microturbulence Project
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| Figure
14 Ion heat conductivity vs. tokamak
minor radius. |
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The goal of this research is to develop computational tools
that will advance the understanding of microturbulence and its
role in the confinement of fusion plasmas. The development of
tools in this project will advance the interpretation of experimental
confinement data and will be used to test theoretical ideas
about electrostatic and electromagnetic turbulence.
Accurate prediction of the heat and particle transport level
is critical for the design of fusion reactors. Current reactor
design studies rely on extrapolations of turbulent transport
properties from present-day tokamak experiments to larger
devices. However, simulations of full-size reactors, only
recently made possible by efficient algorithms and terascale
computers, have found that these extrapolations can be unreliable.
Simulation results reported by Lin et al. show that the ion-temperature-gradient
turbulence fluctuation scale length is microscopic and independent
of device size, that test particle transport is diffusive,
and that the local transport coefficient exhibits a gradual
transition from a Bohm-like scaling for today’s tokamak
sizes to a gyro-Bohm scaling for future larger devices (Figure
14). The device size where this transition occurs is much
larger than that expected from linear theory based on pressure
gradient profile variations.
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Figure
15 Correlation lengths  r
from a set of L-mode discharges and numerical simulations
from the UCAN code. Numerical values are with and without
self-induced or zonal flows.
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An alternative approach to more accurate prediction of microturbulence
is to benchmark and validate plasma simulations through detailed
comparison with experimental measurements. This comparison
relies on implementation of numerical diagnostics that simulate
real-world experimental measurements and analysis techniques.
Rhodes et al. have begun making such comparisons between simulations
and experimental results from the DIII-D tokamak. One of their
findings is that simulations must include self-induced or
zonal flows for agreement with experimental  r
(Figure 15). Although much work remains, the closeness of
the simulation results to experimental measurements so far
is encouraging.
INVESTIGATORS
W. M. Nevins, B. I. Cohen, A. Dimits, and D. Shumaker, Lawrence
Livermore National Laboratory; J. Candy and R. Waltz, General
Atomics; Y. Chen, C. Kim, and S. Parker, University of Colorado,
Boulder; W. Dorland and S. Novakovski, University of Maryland;
W. W. Lee, D. Ernst, G. Hammett, S. Klasky, and J. Lewandowski,
Princeton Plasma Physics Laboratory; Z. Lin, University of
California, Irvine; V. Decyk and J.-N. Leboeuf, University
of California, Los Angeles; V. Lynch, Oak Ridge National Laboratory;
D. Ross, University of Texas; D. Ernst, Massachusetts Institute
of Technology; F. Jenko, IPP Garching.
PUBLICATIONS
Z. Lin, S. Ethier, T. S. Hahm, and W. M. Tang, “Size
scaling of turbulent transport in magnetically confined plasmas,”
Phys. Rev. Lett. 88, 195004 (2002).
T. L. Rhodes, J.-N. Leboeuf, R. D. Sydora, R.
J. Groebner, E. J. Doyle, G. R. McKee, W. A. Peebles, C. L.
Rettig, L. Zeng, and G. Wang, “Comparison of turbulence
measurements from DIII-D low-mode and high-performance plasmas
to turbulence simulations and models,” Phys. Plasmas
9, 2141 (2000).
URL
http://fusion.gat.com/theory/pmp/ |
