Runaway Electrons

During a disruption, electrons can be accelerated to near light speed, forming a damaging beam. Runaway mitigation at 43 MA is a Kronos open item.

What

Electrons accelerated to relativistic energies

When

During the current quench of a disruption

Danger

A focused beam that can damage the wall

Kronos status

Mitigation at 43 MA is an open item

Runaway electrons form during the current-quench phase of a disruption: the strong electric field induced as the plasma current collapses can accelerate a seed population of electrons to near light speed faster than collisions slow them down. The result is a multi-mega-amp beam of relativistic electrons that, if it strikes the wall in a focused spot, can cause serious localized damage.

Because runaway severity grows with plasma current, Kronos MetroVolt's high I_p = 42.5 MA makes this a genuine challenge, and the design series is candid that runaway mitigation remains an open engineering item (flagged in the disruption analyses at 43 MA). It is one of the honestly-ranked open questions the gate program must close, alongside disruption thermal and electromagnetic loads.