A Study of Shattered Pellet Injection Scheme Using Multiple Injection System In KSTAR

ITER plans to systematically inject multiple shattered pellets to reliably dissipate thermal and electromagnetic energies which are rapidly released in a plasma disruption. It is expected that the effectiveness of disruption mitigation in ITER will heavily depend on the material composition of the pellets and also their injection timing since, depending on the order of injection, subsequent pellets will encounter plasmas of completely different properties. KSTAR with two shattered pellet injectors (SPIs) which form a symmetry in the toroidal direction can independently inject three different pellets from each SPI. KSTAR has conducted experiments to validate the disruption mitigation scheme of ITER using multiple shattered pellets by varying their composition and timing. For instance, in order to prevent runaway electron generation, when pure deuterium pellets are first injected and then Ne-doped pellets follow them, there is a tendency to show more localized radiation compared to the case in which only Ne-doped pellets are injected. To measure the characteristics of the plasma during disruption mitigation that happens in a short period of time within a few milliseconds, we also operated dedicated diagnostics that can measure related physical process such as fast bolometry, fast visible camera, and short wavelength interferometry. This result will contribute to establishing efficient injection scheme of ITER.