Electromagnetic and Eddy-Current Codes
Electromagnetic codes compute induced currents and forces in conducting structures during field changes, essential for control and disruption loads.
Induced currents everywhere
Whenever the magnetic field changes, currents are induced in nearby conductors: the vacuum vessel, coil cases, and support structures. These eddy currents shield fields, delay control response, and, during disruptions, carry large forces. Electromagnetic codes compute them by solving the field-and-circuit problem for the conducting structures.
Methods
- Filament and lumped-circuit models for fast, low-order studies
- Finite-element eddy-current solvers for detailed three-dimensional structures
- Thin-shell approximations for vessel walls where thickness is small
Coupling to the plasma
The plasma is itself a moving current source, so control and stability analyses couple the plasma model to the passive-structure electromagnetics. The vessel's eddy currents set the timescale of the vertical instability and shape how fast the plasma responds to control coils, making this coupling central to control design.
Disruption forces
During a disruption, the fast current quench and the flow of halo currents partly through the vessel produce large, sometimes asymmetric, electromagnetic forces. Eddy-current codes coupled to structural analysis predict these loads, which often size the vessel supports and internal component attachments.
Design use
Electromagnetic modeling informs the placement and rating of passive structures and control coils, the achievable speed of position and shape control, and the mechanical loads that structural codes must then check. It is a foundational input to both control and structural analysis.
For any tokamak, including the Hyperion breeder, getting the conducting-structure electromagnetics right is a prerequisite for trustworthy control and load predictions.