Time-dependent SOLPS modeling of helium transport in ITER toward residual gas analyzer

Efficient heating of tritium ions via ICRF relies on helium-3 (³He), whose heating efficiency is sensitive to its concentration [1]. Precise measurement and control of ³He concentration are therefore essential. The ITER Diagnostic Residual Gas Analyzer (DRGA) samples neutral gas from the divertor pumping duct to analyze sub-divertor compositions, with a designed response time of ~1 s, expected to be sufficiently fast for core plasma monitoring based on DIII-D observations [2] and particle replacement time estimates [3]. To investigate the spatial and temporal correlations of ³He across the core, SOL, divertor, and sub-divertor regions (representing the DRGA location), time-dependent SOLPS simulations are performed for ITER fusion power scenarios [4]. For simplicity, ⁴He replaces ³He and is injected via gas puffing at the top crown, mimicking externally supplied ³He rather than fusion ash. The helium injection rate is abruptly doubled or halved from steady-state to evaluate accumulation/exhaust timescales, flow patterns, and spatial correlations. Default and time-dependent B2.5 modes are compared to assess the impact of numerical treatment on predicted dynamics. The helium accumulation timescale predicted by SOLPS is on the order of several hundred milliseconds, roughly a factor of two shorter than empirical estimates and particle replacement time. This discrepancy may be attributed to the simplified geometry used in the simulation [5] or the absence of neutral transport effects between the pumping gap and the DRGA sampling location.