Divertor Heat Flux Control
Keeping the power landing on divertor targets within material limits combines strike-point sweeping, flux spreading, and detachment.
Where the power lands
Exhaust power flows along the scrape-off layer to strike lines on the divertor. The peak heat flux there depends on the total exhaust power, how narrowly it is channeled, and the angle of field-line incidence. The control goal is to keep the peak below the target material's steady-state limit while carrying the required power.
Spreading the load
Several levers spread the heat. Shallow field-line incidence spreads power over more surface. Sweeping the strike point back and forth over the target with the shaping coils averages the load over a wider band. A radiative mantle or detachment removes power before it reaches the surface. Advanced divertor geometries lengthen the flux path to radiate more of the power.
Real-time control
Strike-point position is set by the equilibrium coils, so heat-flux control couples to plasma shape control: the same coils that set the boundary also place and sweep the strike points. Infrared cameras and embedded thermocouples measure the target temperature distribution in real time, and the controller adjusts sweeping and seeding to keep hot spots within limits.
- Peak flux set by power, channel width, and angle
- Sweep strike points to average the load
- Shallow incidence and long legs spread heat
- IR and thermocouples close the loop on target temperature
Interlocks
If the target exceeds a temperature limit despite mitigation, an interlock reduces heating power or terminates the pulse to prevent surface damage. This makes divertor thermal monitoring a protection function, not only a control input. In the Kronos breeder design study, divertor loading is a central engineering constraint for a high-power spherical tokamak; the machine is a simulation and design case, and these behaviours are described generically.
Heat-flux control is the practical limit that heating, fueling, and shaping all have to respect.