Preparation of KSTAR pellet injection system for advanced plasma scenarios

The 20 Hz pellet injection system (PIS) was installed at KSTAR (Korea Superconducting Tokamak Advanced Research) in 2016. The pellet injector has already demonstrated its ability to continuously produce deuterium ice rods and inject pellets at a frequency of 20 Hz for up to 300 s. This system allows for the injection of pellets with varying sizes, velocities, and frequencies, enabling a wide range of plasma experiments at KSTAR. As KSTAR advances toward more complex and high-performance plasma scenarios—incorporating modified PFCs (plasma-facing components) and enhanced heating systems—the pellet injection system must be upgraded accordingly. To support these developments, the PIS underwent maintenance and optimization. Following these improvements, the system achieved reliable pellet injection at approximately 200 m/s across various frequencies, with an operational reliability exceeding 95 %. The density profile during injection was monitored using the TCI (two-color interferometer) system. This paper discusses the current status of the pellet injection system following its regular maintenance and performance tests during plasma experiments. Additionally, we outline plans for further enhancements, including improvements to the vacuum pumping system to support the evolving plasma operation requirements at KSTAR.