Overview of shattered pellet injection studies at ASDEX Upgrade*

Shattered Pellet Injection (SPI) has been selected for ITER as the primary Disruption Mitigation System (DMS). To support the ITER DMS development, a flexible SPI system [1, 2] was installed at ASDEX Upgrade (AUG) to investigate the impact of different fragment size and velocity distributions on the disruption dynamics. In collaboration with the ITER Organization and EUROfusion, we carried out a large experimental campaign with the goal of optimising material assimilation and heat load mitigation. The experiments are also accompanied by modelling with the DREAM, INDEX and JOREK codes, showing good agreement with the experimental observations. With a major update to the radiation measurements of AUG, the investigation of toroidal asymmetries between five toroidal locations is enabled. Of the three shatter head geometries used in AUG plasmas in the 2022 experimental campaign, the 12.5° rectangular shatter head produces relatively large and fast fragments [3], which in turn lead to the highest material assimilation [4] and radiated energy fraction. Simulations suggest that a minor neon doping (<1%) of the otherwise pure deuterium pellets increased the material assimilation via plasmoid drift suppression. We observed the highest impact of the fragment size and velocity distributions on the radiation characteristics in both experiment and simulation for these doped pellets. Otherwise, the radiated energy fraction and (toroidal) radiation asymmetry is a strong function of neon content inside the pellet and only shows a minor dependence on the shatter geometry [5]. The AUG results support the current ITER SPI design [6] with a 15° shatter angle.

[1] M. Dibon et al., Review of Scientific Instruments, 94 (4):043504 (2023).

[2] P. Heinrich et al., accepted manuscript in Fusion Engineering and Design (2024).

[3] T. Peherstorfer, MSc Thesis, TU Wien, 2022.

[4] S. Jachmich et al., 49th EPS Conference on Plasma Physics, Bordeaux, France (2023).

[5] P. Heinrich et al., 49th EPS Conference on Plasma Physics, Bordeaux, France (2023).

[6] M. Lehnen et al., 29th IAEA FEC, TECH/1-1, London, UK (2023).