Low-recycling scrape-off layers (SOLs) can improve core confinement through high edge temperature and low density, but lithium targets evaporate under intense heat loads and collisionless SOL dynamics violate fluid assumptions. Using STEP geometry, the authors combine axisymmetric Gkeyll gyrokinetic simulations, EIRENE neutral transport, and comparisons with SOLPS fluid calculations. The simulations suggest that lithium or another low-recycling material can coat lower-flux side walls while a heat-tolerant target remains high recycling, preserving a hot, dilute SOL without a lithium target. Kinetic parallel dynamics also change exhaust predictions. A large divertor-leg potential confines sputtered impurities downstream more strongly than the fluid model predicts. Mirror trapping combined with drifts broadens the mapped heat-flux width from about
- Proposed separating the low-recycling wall function from the high-heat-flux divertor target material.
- Coupled gyrokinetic plasma and Monte Carlo neutral models for a low-recycling STEP SOL scenario.
- Demonstrated stronger kinetic confinement of sputtered impurities to the divertor region than in fluid simulations.
- Showed that mirror trapping and drifts can broaden the heat-flux channel and reduce its peak.
- Identified helium exhaust and material erosion as unresolved feasibility constraints.