Deep Dive: Current Drive & Bootstrap

Steady-state operation needs the plasma to supply most of its own current. Kronos reaches a bootstrap fraction of 0.59–0.78, topped up by non-inductive drive.

Bootstrap

f_BS = 0.59–0.78 (self-driven)

Non-inductive total

f_NI = 0.61–0.81 at 62 MW

Why

Every self-driven amp saves plant power

Prediction

P7: β_p ≥ 2.2 with f_BS ≥ 0.78

A power plant must run continuously, but the central solenoid can only drive current in a finite pulse — so steady-state operation depends on the plasma supplying most of its own current. This is one of the largest levers on fusion economics.

The self-generated bootstrap current does the heavy lifting: Kronos reaches a bootstrap fraction of 0.59–0.78, meaning the plasma drives well over half its own current for free. The remainder comes from non-inductive current drive — neutral beams and RF (EBW, HHFW) — for a total non-inductive fraction of 0.61–0.81 at 62 MW.

The aligned high-β_p operating point (bootstrap ≥ 0.78) is pre-registered as prediction P7. The remaining current-drive frontier — which launcher, at what efficiency — is priced explicitly rather than assumed, and is among the questions the G1 testbed addresses.