Nuclear analysis of the DEMO divertor survey visible high-resolution spectrometer

Abstract

Spectroscopic measurements have been recently proposed in DEMO for divertor detachment control. In its current design, the DEMO Divertor Survey Visible High-Resolution Spectrometer is foreseen to perform spectroscopy measurements by integrating three optical subsystems into an equatorial port (EP). Behind the first wall, light travels through a set of metallic mirrors and ducts before it reaches the closure plate of the EP. This paper presents a nuclear analysis performed with the Monte Carlo simulation program MCNP6 for two alternative configurations of the system. The results show that the configuration with 5 mirrors per transmission line is very effective to reduce the neutron streaming through the port. However, it will not be possible, with the current design, to introduce standard electronics along the spectroscopy ducts, as the dose rate limits for non-critical electronic components are exceeded in both configurations. In the plasma-facing mirrors, the heat loads are below 2 mW/cm3, which shows that the strategy of recessing the first mirrors and placing them behind small-diameter openings is effective to decrease the loads in the mirrors. FISPACT simulations for different materials show that material transmutation in the mirrors will be negligible throughout the DEMO reactor lifetime.