SOLPS-ITER modelling of plasma discharges in Magnum-PSI with a Lithium Vapor Box Divertor Module

Power exhaust is a significant challenge in the field of nuclear fusion, primarily due to the development of high heat fluxes resulting from elevated particle fluence within fusion reactors. The divertor, a crucial component of fusion reactors, plays a key role in managing and exhausting the power generated by the plasma. Over the years, various divertor configurations have been proposed, and numerous experimental campaigns have been conducted to demonstrate their feasibility in addressing this challenge. In this thesis, the attention will be focused on a particular divertor technology which takes advantage of liquid metals, the so called Liquid Metal Divertor (LMD). Specifically, a Vapor Box (VB) configuration is taken under analysis. This divertor layout, which makes use of liquid lithium, is composed of different chambers that aim to increase plasma collisionality leading to a wider energy and momentum transfer, lowering heat and particle loads to the divertor target. The capability to reduce particle and heat fluxes allows to decrease thermo-mechanical stresses leading to a longer lifetime of the component. The practicability of nuclear fusion technology, particularly in tokamak reactors, relies heavily on the ability to replicate plasma conditions expected within these reactors. Linear plasma devices (LPDs), such as Magnum-PSI, are indispensable in this context as they are capable of reproducing density, temperature, heat, and particle fluxes characteristic of the scrape-off layer (SOL) region in future fusion reactors. Many complex phenomena take place in the edge plasma and SOL region, so numerical models are necessary to investigate plasma behaviour, its interaction with reactor walls and, for the LMD case, with liquid metal particles. SOLPS-ITER represents the code able to describe the plasma evolution in the SOL region by coupling two different approaches: a fluid model, related to the Braginskii’s equations, and a kinetic transport model, which analyses the transport of neutral particles exploiting a Monte Carlo code. This study focuses on the modeling of a lithium Vapor Box Module (VBM) within the Magnum-PSI experimental facility, exploiting the capabilities of the SOLPS-ITER code, which enables to reproduce the complex interactions between lithium and plasma particles. The VBM serves as a novel approach for managing plasma-surface interactions by generating a dense lithium cloud that effectively reduces heat and particle loads on the target surface by increasing collision processes. This device also retains lithium and neutral particles, raising plasma energy and momentum transfer. Simulations were conducted to investigate two distinct scenarios of the VBM, with and without the presence of lithium, aimed at understanding the impact of the liquid metal on the plasma beam. By comparing these two cases, the effectiveness of lithium in mitigating heat and particle loads on the Magnum-PSI target is demonstrated. Furthermore, the preparation of the corresponding validation case, based on the experimental results, is provided.