SOLPS-ITER simulations of a vapour box design for the linear device Magnum-PSI

A vapour box is a physical device currently being considered to reduce the high heat and particle fluxes typically impacting the divertor in tokamaks. This system usually consists of a series of boxes that retains neutral particles to increase the amount of collision events with the impacting plasma. The neutral particles come from recycling and recombination of the plasma, gas puffing inside the box or by the evaporation of a liquid metal, typically Li or Sn. Currently, a vapour box is being constructed for testing in the linear plasma generator Magnum-PSI, operated at DIFFER. Its modular design will allow for open (not enclosing the target) and closed (enclosing the target) configurations, as well as evaporating a liquid metal to create a vapour cloud inside the box. The experiments carried out with this device will investigate its capabilities to reduce the plasma flux towards the target. This work presents a numerical study performed with SOLPS-ITER about the effectiveness of the current vapour box design in its open configuration to retain neutrals and its effect on the plasma beam properties. This is a first step before validation against experiments and studying closed configurations to ensure that the VB can successfully operate in a wide range of plasma parameters. Simulations show that the VB is capable of retaining neutrals and reducing fluxes to the target without requiring additional gas puffing in High and Low plasma flux scenarios. When lithium is evaporated from inside the box, the hydrogen plasma is completely extinguished and replaced by a low temperature \ce{Li} plasma with lower flux. The fraction of Li and Li+ transported upstream the vapour box is three orders of magnitude below the amount evaporated form the central box, as most of the lithium is condensed in the side boxes and another small portion (two orders of magnitude below the amount evaporated) is deposited on the target. The VB design in its open configuration can mitigate incoming plasma peak heat flux by 0.6MW m^-2, which represents a fraction of 75 and 81% for the High and Low flux scenarios. This effect is expected to be higher when a closed configuration is employed, which could result in a significant reduction of heat fluxes on the divertor of tokamaks once that this design is extrapolated to the toroidal geometry, with just a minimal amount of \ce{Li} and \ce{Li+} reaching the core.蒸汽盒（vapour box）是当前正被研究的物理装置，旨在降低托卡马克（tokamak）偏滤器（divertor）通常承受的高热流与粒子流冲击。该系统通常由一系列腔体组成，可滞留中性粒子（neutral particles），以增加其与入射等离子体（plasma）的碰撞频次。此类中性粒子来源于等离子体的再循环与复合、盒内喷气充入，或是典型液态金属（liquid metal，通常为锂（Li）或锡（Sn））的蒸发。 目前，荷兰DIFFER研究所运行的线性等离子体发生器（linear plasma generator）Magnum-PSI正配套建造一台蒸汽盒以开展测试。该装置采用模块化设计，支持开放（不包围靶件（target））与闭合（包围靶件）两种配置模式，同时可通过蒸发液态金属在盒内形成蒸汽云。 依托该装置开展的实验将探究其降低靶件等离子体流的能力。本研究采用SOLPS-ITER开展数值模拟，分析当前蒸汽盒开放配置下的中性粒子滞留效果，及其对等离子体束流特性的影响。这是后续开展实验验证、研究闭合配置的前置步骤，旨在确保蒸汽盒可在宽泛的等离子体参数范围内稳定运行。 模拟结果表明，在高、低等离子体流工况下，蒸汽盒无需额外喷气充入即可实现中性粒子滞留，并降低靶件承受的热流。当从盒内蒸发锂时，氢等离子体将被完全驱散，取而代之的是低通量的低温锂等离子体。 从蒸汽盒上游（upstream）输运的锂及锂离子（Li+）占比，较中央腔体蒸发量低三个数量级；绝大多数锂会在侧腔体中冷凝，仅有极少量（较蒸发量低两个数量级）沉积于靶件表面。 该蒸汽盒开放配置可将入射等离子体峰值热流降低0.6MW·m⁻²，在高、低流工况下分别对应75%与81%的热流削减率。采用闭合配置时的热流抑制效果预计更为显著，若将该设计外推至环形几何结构（toroidal geometry），仅会有极微量的锂及锂离子抵达等离子体芯部（core），可大幅降低托卡马克偏滤器承受的热流负荷。