Extended MHD Codes
Extended MHD codes add two-fluid, gyroviscous, and Hall terms to the ideal picture, capturing physics between single-fluid MHD and full kinetics.
Enriching the fluid model
Single-fluid ideal MHD treats the plasma as one conducting fluid. Real plasmas separate electron and ion dynamics at short scales. Extended MHD augments the equations with two-fluid effects: the Hall term, electron pressure gradient, gyroviscosity, and finite electron inertia. These terms matter at the ion skin depth and ion sound gyroradius, exactly the scales where reconnection and small-scale MHD activity live.
The generalized Ohm's law is the heart of the model. Instead of E plus v cross B equal to eta J, extended MHD adds Hall and pressure terms, which change how field lines slip relative to the bulk flow and can dramatically speed reconnection.
Why the added terms matter
Two-fluid effects introduce dispersive waves (whistlers, kinetic Alfven waves) that alter mode structure and rotation. They set the reconnection rate more realistically than resistivity alone and are needed to reproduce observed island rotation and sawtooth behavior in nonlinear runs.
Numerical cost
The dispersive waves have frequencies rising with wavenumber, which stiffens the equations and forces careful implicit treatment. Extended MHD codes are among the more complex nonlinear MHD tools, and verifying their added terms is a substantial part of code development.
Design relevance
For the Hyperion breeder, extended-MHD simulation refines predictions of tearing and sawtooth dynamics where two-fluid physics changes the growth and rotation, sharpening the control requirements derived from simpler models. This remains design-stage simulation before construction begins Q2 2027.
- Adds Hall, electron pressure, gyroviscous terms
- Generalized Ohm's law governs field slippage
- Captures dispersive waves and fast reconnection
- Stiffer and costlier than resistive MHD