AbstractRunaway electrons can cause severe damage to plasma facing components of large tokamaks. The designs proposed for the first wall and divertor of the next large fusion experiment, ITER-CDA (International Thermonuclear Experimental Reactor - Conceptual Design Activities) are investigated. Energies of up to 300 MeV per electron and surface energy depositions of 30 MJ/m2 are assumed. The GEANT code originating from high energy physics was used to model the energy deposition [J/cm3] quantitatively as a function of the penetration depth and material. The magnetic field was included in the analysis. The energy deposition in the bulk material for a given surface energy load is roughly independent of the incident angle and energy (above 100 MeV) since the main physical process of the energy loss is the formation of an electromagnetic shower, i.e. rapid dissipation of the initial energy into many electrons, positrons and photons. Typical divertor designs protect the cooling tubes with a 1 cm thick graphite layer. Melting of such molybdenum (copper) cooling tubes occurs at a heat load of 50 (25) MJ/m2. Every additional cm of graphite roughly doubles the runaway protection. For low cooling water temperatures (TH2O≈100°C), water pressurization due to runaway electron impact is not a serious problem if the cooling pipes do not melt. If the first material facing the plasma is metallic, melting must be expected for heat loads of around 15 MJ/m2.
runaway电子可对大型托卡马克的等离子体 facing 部件造成严重损伤。本文研究了下一代大型聚变实验装置ITER-CDA（国际热核聚变实验堆-概念设计）第一壁和偏滤器的设计方案。假设每个电子的能量高达300 MeV，表面能量沉积为30 MJ/m²。采用源自高能物理的GEANT代码，定量模拟了能量沉积[J/cm³]随穿透深度和材料的变化。分析中考虑了磁场的影响。对于给定的表面能量负载，体材料中的能量沉积大致与入射角度和能量（高于100 MeV时）无关，因为能量损失的主要物理过程是电磁簇射的形成，即初始能量迅速耗散为大量电子、正电子和光子。典型的偏滤器设计采用1 cm厚的石墨层保护冷却管。当热负载达到50 MJ/m²时，钼（铜）冷却管会发生熔化。每增加1 cm石墨，对runaway电子的防护能力约提高一倍。对于低冷却水温度（TH2O≈100°C），只要冷却管不熔化，runaway电子冲击引起的水压升高并非严重问题。若第一壁 facing 等离子体的材料为金属，则当热负载约为15 MJ/m²时，必须预期会发生熔化。