MHD Simulations with the NIMROD Code

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Table of contents

MHD Simulations with the NIMROD Code


Modern Tokamak Discharges Have Rich Magnetic Behavior

Resistive MHD is Inadequate for Explaining Modern Discharges

What is Needed?

NIMROD Uses "Extended MHD"

Two-Fluid Equations Are Numerically Challenging

Temporal Advance Uses Semi-Implicit Method

Finite-Elements Used for Flexible Spatial Discretization

NIMROD Also Has Flexibility in Finite-Element Basis

Higher-Order Elements Useful For Shaped Geometries

Toroidal Direction Uses Fourier Decomposition

Spheromak Simulations Illustrate Flexibility of NIMROD

Flux Amplification Occurs Due to Dynamo Process

Axisymmetric components show relaxation towards Taylor state

Despite Taylor Relaxation, Fields Largely Chaotic

Dominant Mode Saturated n=1 Pinch Instability

Decaying Spheromaks Form Flux Surfaces

Vacuum Region Necessary for Correct Stability Boundary

NIMROD Models Vacuum As Very Resistive Plasma

Model Gives Good Linear Convergence

Eigenfunctions Converge For Increasing Resistivity

Status of Vacuum Implementation


Summary (continued)

NIMROD is for the Community

Author: Scott Kruger