Radiated-Power Control

Radiated-power control regulates how much and where the plasma radiates, protecting surfaces without collapsing the core.

Radiation as a lever

A plasma radiates power through impurity line emission, bremsstrahlung, and recombination. Radiation is useful when it happens in the edge and divertor, spreading exhaust heat over a large area. It is harmful when it happens in the core, where it drains energy meant to sustain fusion. Radiated-power control manages this balance.

Measurement

Bolometer arrays measure the radiated power along many lines of sight, and tomographic inversion reconstructs where the radiation comes from. In real time, a reduced version of this gives the controller both the total radiated fraction and a coarse map of where radiation is concentrated, edge versus core.

The control target

A common target is to hold the edge radiated fraction at a set value, high enough that the divertor is protected but low enough that the radiation front stays out of the confined plasma. Impurity seeding rate is the main actuator. The controller must respond before a rising front reaches the core and cools it.

Coupling

Radiated-power control overlaps divertor-detachment control and impurity control, since all three act on seeding and edge radiation. They are often implemented as one coordinated controller with several outputs rather than three independent loops fighting over the same actuator. Core radiation is handled by different levers, chiefly central heating and sawtooth flushing.

In the Kronos program

The Hyperion breeder uses edge radiation to protect its divertor while guarding the core against radiative collapse. Its radiated-power controller is coordinated with detachment and impurity control on the shared seeding actuators. The target radiated fraction and the control response are set through edge modeling in simulation ahead of operation.