First-Wall and Divertor Health

Tracking erosion, deposition, and thermal fatigue of the plasma-facing components that set how long a campaign can run.

The components that touch the plasma

The first wall and divertor absorb heat and particle flux from the plasma and, in the breeder, the 14 MeV neutron load. Their gradual degradation - erosion, redeposition, thermal fatigue, neutron-induced changes - sets a hard ceiling on how long a campaign can run before an inspection opening. Tracking their health turns that ceiling from a surprise into a schedule.

Health indicators

• Surface temperature maps from IR thermography during shots
• Erosion and deposition inferred from spectroscopy and periodic metrology
• Thermal-fatigue cycle counting weighted by local heat flux
• Neutron-fluence accumulation as a damage proxy for the breeder

These indicators feed a per-tile RUL model. Because heat flux is uneven - the divertor strike point and the negative-triangularity delta -0.30 scrape-off geometry concentrate load - the model is spatial, tracking the worst tiles rather than an average.

def tile_damage(heat_flux_map, dt, fatigue_exp=4.0):
    # accumulate weighted thermal-fatigue damage per tile (Coffin-Manson-like)
    return (heat_flux_map ** fatigue_exp) * dt   # elementwise, worst tile drives RUL

Feeding the schedule

The worst-tile RUL sets the campaign length; predictive maintenance places wall or divertor service in the opening before that tile is predicted to fail. For the burner the neutron fraction is lower (5.44%) so neutron damage is less dominant, but plug-adjacent thermal loading is un-characterized in the 166-830x regime and is therefore tracked conservatively. All estimates are reconciled against teardown and propagated across the fleet.