Magnet Requirements for MHD Conversion

MHD power density scales with field squared, so the burner's 26.49 T plug and 17 T throat magnets are what make compact MHD conversion feasible.

Field is the lever

The power that an MHD channel can extract per unit volume scales roughly with the square of the magnetic field and with the plasma conductivity. Doubling the field, all else equal, quadruples the available power density. That is why classical MHD generators struggled: ordinary electromagnets could not reach the fields needed for a compact, efficient channel. The burner does not have this problem — it is built around ultra-high-field superconducting magnets.

Borrowing the confinement magnets

The tandem-mirror confinement already requires these intense fields: 26.49 T at the plug to build the electrostatic barrier that holds the ions, and 17 T at the throat. The MHD conversion channel can sit in the expanding-field region of this same magnetic system, so the high field needed for conversion is provided by the confinement architecture rather than a separate magnet system.

Superconductor demands

• High-field operation implies high-temperature superconductor (REBCO-class) magnets to reach 26.49 T.
• The magnets must tolerate the burner's neutron fraction (~5.44%) with adequate shielding.
• Field grading from 26.49 T to the expander region shapes both confinement and the conversion channel.

The coupling to conversion

Because the same magnetic field both confines the plasma and drives the MHD conversion, the two cannot be designed independently — the field profile that best holds the plasma also sets where and how well MHD conversion can occur. This tight coupling is characteristic of the burner and is one reason it is treated as an integrated design-and-simulation study rather than a set of bolt-on subsystems.