Deep Dive: The Confinement Case

The design needs H98 = 1.84, resting on negative triangularity, the hot-ion posture, and density headroom — anchored on DIII-D data, with the nonlinear gyrokinetic check outstanding.

Requirement

H98 = 1.84 (profile basis)

Basis

Reduced-order chain + DIII-D NT database

Reduced check

TGLF (S16/S18, HPC-pending)

Load-bearing

Nonlinear CGYRO/GYRO — outstanding

Confinement is the single largest bet in the Kronos design, so it deserves a careful look. The plant needs a confinement multiplier of H98 = 1.84 over the standard IPB98(y,2) scaling — meaning it must confine energy 84% better than a conventional plasma of the same size and power.

Three pillars support that requirement: negative triangularity (which reshapes and reduces turbulence), the hot-ion posture (which raises the ITG turbulence threshold ~1.3×), and operation at high density. The empirical anchor is the 2023 DIII-D negative-triangularity campaign, which demonstrated H-mode-grade confinement with an L-mode edge.

The honest caveat, stated plainly throughout the design: this requirement is quoted from reduced-order models (TGLF, S16/S18) and the DIII-D database, not from completed nonlinear gyrokinetics. The load-bearing verification — a nonlinear CGYRO/GYRO study — remains outstanding and is the first measurement the G1 testbed exists to make.