Divertor Heat-Flux Modeling
Divertor modeling predicts the concentrated heat and particle loads on exhaust targets and the mitigation needed to keep them within material limits.
The exhaust challenge
Power leaving the core plasma flows along a thin layer of open field lines and strikes the divertor targets over a narrow footprint. The resulting peak heat flux can rival that on a spacecraft heat shield. Predicting and reducing it is one of the defining engineering problems of a high-power fusion device.
The heat-flux width
The peak load depends on how wide the exhaust channel is when it reaches the target. This heat-flux width is set by cross-field transport competing with parallel flow along field lines. Empirical scalings and edge simulations both estimate it, and its extrapolation to new devices carries real uncertainty.
Mitigation strategies
- Detachment, dissipating power by radiation and neutral interactions before the target
- Impurity seeding to enhance radiative cooling in the divertor
- Magnetic geometry that flares or spreads the strike region
- Sweeping the strike point to distribute the load in time
Modeling toolchain
Edge fluid codes predict the plasma conditions and heat load at the target; thermal and structural codes then check that the target material and cooling can handle it. Coupling these gives an end-to-end assessment from core exhaust power to component temperature, the basis for divertor design.
Transient loads
Beyond the steady load, transients from edge-localized modes and disruptions deliver brief but intense pulses. Modeling these requires the stability and disruption codes together with the thermal response of the surface, since transient melting or ablation can limit component life.
Exhaust modeling is part of confirming that any design, including high-power breeder and burner concepts, can handle the power it must reject.