Neutral-density dependence of EIR- and MAR-dominated detachment regimes in hydrogen plasmas with multi-ion-temperature effects

A multi-ion-temperature model for hydrogen plasmas has been newly developed and implemented in the linear divertor plasma simulation code LINDA-NU to investigate detachment mechanisms involving atomic and molecular processes. In this model, H+, H2+, and H3+ ions are treated as separate fluids with independent temperatures, enabling a detailed assessment of ion-species-dependent thermal and momentum dynamics in detached plasmas. Plasma detachment transitions were studied by scanning atomic and molecular neutral densities. An increase in atomic hydrogen density leads to electron–ion recombination-dominated detachment, where charge exchange with atomic neutrals governs momentum loss. In contrast, increasing molecular hydrogen density results in molecular-activated recombination (MAR)-dominated detachment, in which molecular ions become quantitatively significant and strongly influence particle, momentum, and energy balances. A comparison with a simplified single-ion-temperature model demonstrates that the multi-ion-temperature treatment is essential for accurately describing the MAR-dominated regime, where multi-ion temperatures significantly modify molecular reaction rates, leading to qualitative differences in plasma profiles.