Operating Narrative: Cold Start

A plain sequence from a fully cold machine to first plasma, and every point where the stack can hold, abort, or safe the plant.

From cold iron to first plasma

A cold start is the highest-risk routine operation because nearly every subsystem transitions state at once. The stack sequences it as a guarded state machine: each phase has entry conditions, an abort path, and a timeout. Nothing advances until the twin confirms the prior phase converged. This narrative applies to the breeder (Hyperion); the burner variant is in the burner narrative.

Ordered phases

• Vacuum and bake: pump to base pressure, confirm leak rate within budget
• Cryogenic cooldown: superconducting magnets to operating temperature, watched by quench diagnostics
• Magnet energization: ramp toward 16.84 T peak field (8 T on-axis) with continuous normal-zone monitoring
• Gas fueling and breakdown: admit deuterium, apply loop voltage, initiate breakdown
• Current ramp: drive plasma current toward 9.66 MA while holding vertical stability at delta -0.30
• Flat-top: establish the target scenario and hand over to shot control

PHASES = ['vacuum','cooldown','energize','breakdown','ramp','flattop']
def cold_start(twin):
    for ph in PHASES:
        enter(ph)
        if not twin.converged(ph, timeout=phase_timeout[ph]):
            return safe_abort(ph)      # hold in last safe state
    return 'flattop_ok'

Where it can stop

At any phase the twin can raise a hold (recoverable pause), an abort (retreat to the prior safe state), or a safe (drive the whole plant to a defined low-energy configuration). Magnet energization is the most consequential gate: a normal-zone signature during the ramp triggers a protective discharge rather than a retry. See Quench Detection and Safe States.

Because Hyperion is a design-and-simulation study before FOAK ~2030, cold-start is exercised entirely against the digital twin with injected faults at each phase boundary, building the guard logic that will run on hardware.