Experimental environment for testing the shattered pellet injection of KSTAR

The dual shattered pellet injection (SPI) systems installed at the KSTAR (Korean Superconducting Tokamak Advanced Research) have been operational since 2019 to conduct disruption mitigation studies in support of ITER DMS (Disruption Mitigation System) design activities. The system has the advantage of firing pellets simultaneously from the two identical pellet injectors installed at 180-degree opposite positions on KSTAR. Each injector is capable of fabricating and firing three pellets of different sizes (diameter, length). The characteristics of the initial pellet (geometry, velocity, etc.) can be verified using a microwave cavity (MWC) system and an imaging optical pellet diagnostics (OPD) system. Each SPI system must achieve specific conditions related to pellet fabrication and firing prior to plasma experiments. We realized that we didn't have the sufficient time and conditions to do off-line testing in 2022, so we have developed a suitable solution. First, we have to disconnect the SPI system from the KSTAR vacuum vessel and build a separate test chamber in the injection line. Inside the new test chamber, we have to install the same shatter tube used in the current experiments and equip it with measuring devices to observe the fragmented pellets. We also have to switch the fabrication process of the pellets from manual to semi-automatic using a feedback pressure controller on the barrel pressure. In this paper, we will describe the new experimental environment for independent SPI testing and the future plan.