Description
Shattered Pellet Injection (SPI) is the primary Disruption Mitigation System (DMS) for ITER [1], the main purpose of which is the mitigation of thermal loads during the Thermal Quench (TQ) phase of disruptions. Aside from the heat load mitigation, SPI would also aim for helping with Current Quench (CQ) phase runaway electron avalanche suppression. To achieve both goals, deep and reliable penetration of injected materials into the axis region is desirable, as such deep deposition would ease the radiation heat flux asymmetry onto the first wall as well as increase the electron collision rate in the high current density region.
However, recent progress shows that more realistic consideration of pellet shattering as well as the subsequent ablation within the plasma could have significant impact on SPI penetration and material assimilation. On one hand, in the high injection velocity limit, the pellet shattering could leave only 1/3 of the original mass in the solid fragment plume [2], the rest is turned to dust, droplets or gas which could not penetrate deeply into the core. On the other hand, the plasmoid drift and the background plasma temperature gradient could cause an asymmetry in the ablation cloud around the fragments such that the ensuing pressure asymmetry acts as a “rocket force” on the fragment [3], which could change the fragments’ trajectory significantly if the they are small enough and slow enough. Furthermore, if the injection velocity is too slow, the TQ may set in prematurely before the fragments reach the core, imposing a lower limit on the injection velocity.
To investigate the most desirable injection scenario, JOREK 2D and 3D simulations are carried out in this study, incorporating realistic fragment plume distributions provided by dedicated shattering simulations [2] as well as a fitted model of the rocket force from the PELOTON code [3] applicable to ITER. The penetration and radiative cooling after SPIs with various combinations of injection velocity, mixture-ratio and injectors are compared in the 2D parameter scan and 3D simulations are carried out for the most relevant scenarios to evaluate the ultimate TQ mitigation efficacy.
[1]. M. Lehnen, K. Aleynikova, P.B. Aleynikov et al., “Disruptions in ITER and strategies for their control and mitigation” J. Nucl. Mater., 463, 39-48 (2015).
[2]. P. Matura, “Technical Report (D03) - Simulations of ITER pellets and shatter geometry”, IDM-5KX6U2, 2025
[3]. J. Corbett, R. Samulyak, F J Artola et al., “Numerical model for pellet rocket acceleration in PELOTON”, Plasma Phys. Control. Fusion, accepted (2026)