Massive Gas and Pellet Injection Timing

The mitigation actuators must open, deliver, and take effect on a schedule tight enough to radiate the plasma's energy before it lands on the wall.

The actuator side of mitigation

Disruption mitigation on the breeder relies on rapidly introducing material — massive gas injection and/or shattered pellets — to radiate the plasma's stored thermal and magnetic energy uniformly instead of dumping it on a small area. The timing constraint is that the mitigating radiation must begin before the thermal quench deposits energy on plasma-facing components.

def injection_ok(open_delay_ms, transit_ms, assimilate_ms, budget_ms):
    delivered = open_delay_ms + transit_ms
    effective = delivered + assimilate_ms
    return effective <= budget_ms, effective

ok, t = injection_ok(open_delay_ms=0.5, transit_ms=1.0,
                     assimilate_ms=1.5, budget_ms=8.0)
assert ok

Why pre-arming matters

The valve or pellet mechanism has an irreducible mechanical opening delay. If the injector is only armed at the moment mitigation is decided, that delay is spent inside the disruption budget. Kronos pre-arms the injectors when avoidance confidence falls, so that at the decision instant only the fire command remains — converting a mechanical delay into a near-instant release.

• Multiple injectors distributed toroidally give redundancy and more uniform assimilation.
• Pre-arm on falling avoidance confidence; fire on the mitigation trigger.
• Fail-safe on the injector itself: loss of hold releases toward the safe (mitigating) action.

Injector siting is a safety parameter, not just a plumbing choice: toroidally distributed injectors deliver material more symmetrically, which improves assimilation and lowers the force-peaking that drives structural loads during the shutdown. The design therefore treats the number, placement, and independent firing of injectors as part of the mitigation's safety margin, and the reflex tier can fire subsets to keep delivering material even if one injector is unavailable.

Uniform assimilation is what keeps the halo current and force limits and runaway electron hazards in check; a poorly timed or asymmetric injection can worsen both. The overall schedule must fit the precursor-to-actuation latency chain.