MHD Stability

Magnetohydrodynamic stability sets the boundaries of safe operation; staying within them is what keeps the 9.66 MA plasma confined and disruption-free.

The stability boundaries

A magnetically confined plasma is subject to magnetohydrodynamic (MHD) instabilities, collective motions driven by current and pressure gradients that can distort or terminate the plasma. Every tokamak operating point sits inside a boundary set by these modes: exceed a current, pressure, or shape limit and an instability grows. Designing Hyperion means placing its operating point safely inside that boundary.

What drives instability

Two main energy sources feed MHD modes: the plasma current, which drives current-gradient (kink and tearing) modes, and the plasma pressure, which drives pressure-driven (ballooning) modes. High current and high beta, exactly what make Hyperion productive, also push toward these limits, so performance and stability are in direct tension. The current and pressure profiles are shaped to widen the stable window.

Shape and control

Plasma shape strongly affects stability, and Hyperion's elongation and negative triangularity are chosen partly for their MHD behavior, including softer edge modes. Active control of the vertical position and, where needed, of specific instabilities keeps the plasma inside its limits during a discharge. Validating the predicted stable operating window at 9.66 MA and the design beta is a core objective of the simulation program and the first-of-a-kind campaign.

• MHD modes bound the safe operating point
• Current drives kink/tearing; pressure drives ballooning
• Shape and active control widen and hold the stable window

This page describes a design and simulation study, not a built machine. Construction begins Q2 2027; first-of-a-kind first tritium is targeted near 2030.