Numerical Investigation of Impurity Seeded Radiation Enhancement in the Divertor region with Magnetic Perturbations in ASDEX Upgrade

摘要

Introduction Currently one of the most promising concepts for future fusion devices, such as ITER and DEMO, is the divertor tokamak, in which power and particles leaving the confined region are transported to the divertor targets. The power flux to the targets can locally exceed the tolerable target heat flux limit and it is therefore required that a large fraction of the power is dissipated before reaching the target. It has been shown in various experiments that this goal can be achieved by seeding low to medium Z impurities [2]. In [3] an empirical scaling formula for the power radiated by the nitrogen impurities has been found that depends linearly on the power decay length λ_q [1]. One way to increase λ_q could be the application of Magnetic Perturbations (MPs). MP coils were introduced at ASDEX Upgrade (AUG) and a number of other tokamaks to study their mitigating effect on Edge Localized Modes (ELMs) [4], intermittent high power flux bursts which can pose a serious risk for the targets. MPs can change the magnetic topology strongly and lead to the formation of stochastic regions inside the separatrix and finger-like deformations of the separatrix, so called lobes. To study numerically how the application of MPs affects the impurity radiation in the SOL and divertor, the edge code EMC3-Eirene [5] was employed to simulate an AUG L-mode deuterium bulk plasma with and without MPs. Subsequently nitrogen seeding simulations were performed on these bulk plasmas and the impurity radiation distribution between the MP-on and off cases considered in detail.