1998 Annual Report
Fusion Energy Sciences

Three-Dimensional Magnetohydrodynamics Studies of Tokamak Fueling

H. R. Strauss, New York University
W. Park, Princeton Plasma Physics Laboratory

 

Research Objectives

Tokamaks are the leading confinement concept for magnetic-fusion energy. The strong magnetic field in the donut-shaped tokamak confines the ionized hydrogen isotopes as they are heated to temperatures of over 10,000 eV and undergo fusion reactions. One of the objectives of present-day tokamak research is to develop efficient means of injecting cold fuel into the core of the tokamak to replace what is being burned. Recent experimental results indicate that if pellets of cold fuel are injected from the outside of the tokamak (the low field side), they are immediately expelled without reaching the center, while if the pellets are injected from the inside (i.e., the hole of the donut, or the high field side) the fuel does reach the high-temperature center where it is needed. Our objective was to reproduce this effect in a 3D simulation code to better understand and optimize it.

Computational Approach

We use the MH3D code, which is a very flexible code system for solving the magnetohydrodynamics (MHD) equations in three space dimensions and time. Existing code options allow several representations of a plasma, ranging from a conducting fluid to a collection of interacting charged particles with long mean-free-paths. The most efficient way to represent general spatially localized perturbations is to use an unstructured numerical mesh. We call the recently developed unstructured-mesh, finite-element version of the MH3D code "MH3D++." It has been used to model both inside and outside pellet injection.

Accomplishments

Nonlinear 3D simulation results show that the MHD forces will accelerate pellets, causing those injected on the low field side of a tokamak (i.e., the outside) to be expelled, and those injected on the high field side to be transported to the plasma center. This can also have the secondary effect of reconnecting the magnetic field into a reverse shear configuration.


Simulated penetration of a fuel pellet, localized in three dimensions, into a tokamak.


These computational results are in qualitative agreement with the experimental results from the ASDEX tokamak, which have shown that pellets injected on the inboard, low major radius edge suffered less loss, and were absorbed more completely into the plasma.

Significance

Computational simulations provide a bridge between theory and experiment, helping to predict and optimize performance in future tokamak experiments.

Publications

H. R. Strauss and W. Park, "Magnetohydrodynamic effects on pellet injection in tokamaks," Phys. Plasmas 5, 2676 (1998).


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