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What is the G1 confinement testbed?
G1 is a sub-scale spherical tokamak — the first Kronos gate — built to measure the design's load-bearing confinement and hot-ion predictions before scaling up.
G1 is where the Kronos design meets reality. It is the first and most important gate, and the answer to nearly every "but is the confinement real?" question — see the biggest technical risk.
Questions & answers
What is the G1 testbed?
G1 is a sub-scale negative-triangularity spherical tokamak (magnetic field 3 T, major radius 0.85 m, plasma current ~5 MA) built to test the physics the whole design rests on. It takes about four years to first plasma, and produces its confinement database about four years after that.
What does it measure?
The load-bearing predictions: negative-triangularity confinement (P1), the hot-ion posture (P2), aligned high-β_p sustainment (P7), current-drive efficiency, and the fast-ion channeling proof-of-principle (P6). It is designed to sit within 1.7× of the full plant's normalized gyroradius so the results transfer.
Why build a sub-scale machine first?
To retire the biggest physics risk before committing to a full-scale plant. G1 tests the scaling; only the full plant tests the value. It is the single most consequential step in the program.