Serpent neutronics model of Wendelstein 7-X for 14.1 MeV neutrons

TL;DR

This paper develops a Serpent 2 neutronics model of the Wendelstein 7-X stellarator to evaluate 14.1 MeV neutron flux and detector response, providing insights into neutron behavior and scattering effects within the device.

Contribution

It introduces a novel unstructured mesh geometry model for W7-X and offers first insights into fast neutron scattering and detector response in this stellarator.

Findings

Superconducting coils are primary scatterers blocking neutrons.

Back-scattering from steel supports is minimal.

SciFi detector can observe neutrons from extended plasma volume.

Abstract

In this work, a Serpent 2 neutronics model of the Wendelstein 7-X (W7-X) stellarator is prepared, and an response function for the Scintillating-Fibre neutron detector (SciFi) is calculated using the model. The neutronics model includes the simplified geometry for the key components of the stellarator itself as well as the torus hall. The objective of the model is to assess the 14.1 MeV neutron flux from deuteron-triton fusions in W7-X, where the neutrons are modelled only until they have slowed down to 1 MeV energy. The key messages of this article are: demonstration of unstructured mesh geometry usage for stellarators, W7-X in particular; technical documentation of the model and first insights in fast neutron behaviour in W7-X, especially related to the SciFi: the model indicates that the superconducting coils are the strongest scatterers and block neutrons from large parts of the plasma. The back-scattering from e.g. massive steel support structures is found to be small. The SciFi will detect neutrons from an extended plasma volume in contrast to having an effective line-of-sight.