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Deep-dive
Deep Dive: MHD Stability
A survey of the stability limits Kronos must respect — kink, ballooning, vertical, and resistive-wall modes — and how the design stays inside them at β_N = 4.96.
- Kink
- q95 ≥ 5.0 keeps it safe (S21)
- Ballooning/Mercier
- Pressure limits (S23)
- Vertical
- Margin 2.02 (S24/S69)
- RWM
- Feedback holds the wall-stabilized β_N ≤ 5.0 regime (S22/S25) — load-bearing
Magnetohydrodynamic (MHD) stability sets the hard limits on how much pressure and current a plasma can hold before it disrupts. Kronos's deposited analyses walk through the whole chain:
- Kink modes — current-driven; held off by a wide q95 ≥ 5.0 margin (no-wall kink limit, S21).
- Ballooning & Mercier — pressure-driven; assessed for second-stability access (S23).
- Vertical stability — the κ = 2.56 elongation is held with a 2.02 control margin (S24, S69).
- Resistive wall mode — the high-β instability, controlled by active feedback to reach toward the wall-stabilized limit (S22, S25).
The binding constraint is the Troyon beta limit: the ratified Mode-D point operates at β_N = 4.96 inside the wall-stabilized regime, against the computed β_N ≤ 5.0 limit that RWM control makes load-bearing (the S79-priced envelope the re-basis adopted; the Mode-C-era 4.33/4.5 posture is labeled history). Every one of these limits is deposited and checkable.