Simplified conductance model for the subdivertor of Wendelstein 7-X based on high-fidelity simulations and comparisons with experimental data

The neutral gas pressure distribution in the subdivertor plays a crucial role for the investigation of particle exhaust in plasma experiments and is provided using the Direct Simulation Monte Carlo solver within the DIVGAS framework for Wendelstein 7-X. However, DIVGAS simulations are time-consuming and require large amounts of computational resources. DSMC simulations are therefore only accessible for a few selected plasma scenarios. This work presents a simplified, linear conductance model for the subdivertor of Wendelstein 7-X in which the neutral gas pressure at a given location in the subdivertor is used to calculate the neutral gas pressure at other locations. The conductance parameters were derived from previously existing DIVGAS cases for the standard and high iota magnetic field configuration and therefore do not require a quantitative description of the subdivertor geometry or the pumping systems. The model allows for predictions of the neutral gas pressure at chosen subdivertor locations including both pumping gaps, the AEH and AEP pumping ports and the AEI port with an average deviation of below 10% for the standard and below 15% for the high iota configuration compared to the DIVGAS dataset. Application to experimentally measured neutral gas pressures of the plasma campaign OP1.2b yields average deviations of up to 77.2% in standard and up to 261.9% in high iota configuration. Thus, the simplified conductance model presents a viable framework for estimating the neutral gas pressures at locations relevant for particle exhaust but not covered by experimental measurements, e.g. near the cryo-vacuum pumps. If used in conjunction with plasma-edge codes, it can provide access to the neutral gas pressure at certain subdivertor locations and thus extend codes to include predictions of particle exhaust.