Abstract
Abstract
Shattered pellet injection (SPI) is one of the prime candidates for the ITER disruption
mitigation system because of its deeper penetration and larger particle flux than massive gas
injection (MGI) (Taylor et al 1999 Phys. Plasmas 6 1872) using deuterium (Commaux et al
2010 Nucl. Fusion 50 112001, Combs et al 2010 IEEE Trans. Plasma Sci. 38 400, Baylor
et al 2009 Nucl. Fusion 49 085013). The ITER disruption mitigation system will likely
use mostly high Z species such as neon because of more effective thermal mitigation and
pumping constraints on the maximum amount of deuterium or helium that could be injected.
An upgrade of the SPI on DIII-D enables ITER relevant injection characteristics in terms of
quantities and gas species. This upgraded SPI system was used on DIII-D for the first time in
2014 for a direct comparison with MGI using identical quantities of neon.
This comparison enabled the measurements of density perturbations during the thermal
quench (TQ) and radiated power and heat loads to the divertor. It showed that SPI using
similar quantities of neon provided a faster and stronger density perturbation and neon
assimilation, which resulted in a lower conducted energy to the divertor and a faster TQ onset.
Radiated power data analysis shows that this was probably due to the much deeper penetration
of the neon in the plasma inducing a higher core radiation than in the MGI case. This
experiment shows also that the MHD activity during an SPI shutdown (especially during the
TQ) is quite different compared to MGI. This favorable TQ energy dissipation was obtained
while keeping the current quench (CQ) duration within acceptable limits when scaled to ITER.
