Relating upstream SOL temperature and density profiles to downstream ion flux profiles and pumping efficiency

Experiments on DIII-D over a range of plasma current and densities are used to examine two-point model estimates for downstream ion flux profiles used in estimating cryopump coupling. Density control via cryo-pumping in present-day machines requires coupling a portion of the recycled neutrals into a plenum entrance to be exhausted that would otherwise re-fuel the plasma. In attached conditions, this requires creating baffling geometry to accept large fraction of the ion flux. The ion flux width, ??_Γ, can be related to the heat flux width, ??_q through the ITPA scaling by assuming fixed or a range of values for ??_n/??_T, representing the temperature and density fall-off lengths through the two-point model assuming equipartition. In low recycling attached conditions, ??_n/??_T~1-1.5, but this ratio can increase as overall density increases to high recycling and detached conditions. In the limit recycled neutrals do not ionize prior to entering the plenum, the characteristic factor of ??_Γ entering the divertor plenum can be estimated for the best particle exhaust. We use a range of plasma conditions varying plasma current and density governing the width of the SOL quantities to examine these relations.