Development of the new KSTAR helium distribution box

•There has been progresses in the construction and 1st operation of DBU in 2016 KSTAR plasma experiments.•Two in-vessel cryopumps (CPIs) cool-down to 4.5K and observed pumping speed was 3.0E4l/s.•Manual CPI regeneration tests were accomplished regarding future automatic control.•Production of the D2 pellets were successful and there has been lots of injection tests. KSTAR project has required the new helium distribution box named upgraded distribution box (DBU) for the operation of the cryogenic components such as in-vessel cryo-pump (CPI), super-sonic molecular beam injector (SMBI), and deuterium pellet injection system (PIS). Two CPIs are inserted into the tokamak vacuum vessel and these components shall be operated at 90K for the liquid nitrogen thermal shields and 4.5K for the hydrogen cryo-panel. One hydrogen PIS was newly mounted on the tokamak for the 2016 KSTAR campaign. Liquid nitrogen shall be supplied to the one SMBI. For the operation of above mentioned 3 kinds of cryogenic components, a helium refrigerator, which had been used for the R&D in the KSTAR facility construction phase (2002–2013), was moved and inserted into the KSTAR 9kW helium facility room. The cooling capacity of the refrigerator at 4.5K is 1kW and it was manufactured from the Linde Kryotechnik before 2002. After some maintenances in warm compressor, electrical power supply, oil-filter, and so on, commissioning of the refrigerator up to 4.5K was accomplished successfully. From the beginning of 2015, design and fabrication of the DBU was started. It shall control the liquid nitrogen for the SMBI and CPI thermal shields whereas liquid helium for the CPI cryo-panel and PIS. To minimize the temperature of the liquid nitrogen to be supplied to SMBI and CPI, a thermal damper tank was inserted into the distribution box. Nitrogen return gases are to be warmed up to room temperature at the heater in the distribution box. A 1000l of liquid helium vessel is located nearby the PIS to supply cold gas helium (∼5K). Because the CPI cryo-panel requires regeneration up to 90K, complex regeneration and re-cool down scenario was developed and applied to the DBU. Including operational results, details of the DBU progresses will be reported in this paper.