Commissioning of vacuum pumping devices of the second KSTAR neutral beam injection system

Abstract The Korea Superconducting Tokamak Advanced Research (KSTAR) Neutral Beam Injection (NBI) system is designed to provide additional plasma heating and current drive for high performance and long pulse operation of the KSTAR tokamak using two co-current beam injection systems. Each neutral beam injection system is designed to consist of three ion sources, and each ion source is designed to deliver more than 2.0 MW of deuterium neutral beam power for the 100 keV beam energy. Consequently, the final goal of the KSTAR NBI system is to inject 12 MW of deuterium beam power for the long pulse operation of the KSTAR. The first NBI (NBI-1) has been installed since 2010, which provides a 100 keV deuterium neutral beam of 6.0 MW maximum using three ion sources. The second NBI (NBI-2) also consist with three ion sources which arranged vertically with tangency radius of 1.56 m to provide balanced core heating and off-axis current drive will be constructed until 2019. An ion source will be commissioned 2018 KSTAR campaign, and the other two ion source will be applied to KSTAR from 2019. As the vacuum condition can substantially affect the beam performance, the vacuum pumping system for NBI-2 has been carefully designed. The cryopumps for NBI-2 were designed and the overall vacuum pumping system of NBI-2 was installed including turbo pumps, mechanical booster-pumps, and dry-pumps. In this paper, the detailed engineering design, fabrication, and installation results of large condensation cryopumps and vacuum sub-components were explained. The effective pumping speed and pressure distribution will be evaluated through the commissioning of the vacuum pumping system for NBI-2. Finally, we present the operation procedures of the NBI-2 vacuum pumping system.