Hirotaka NAKAI is a professor of the Accelerator Laboratory at the High Energy Accelerator Research Organization (KEK), Japan, and also a professor of the School of High Energy Accelerator Science at SOKENDAI (The Graduate University for Advanced Studies), Japan. He leads the cryogenic group of the Accelerator Laboratory for operation, maintenance and management of the cryogenic systems for superconducting radio frequency accelerating cavities operating at 4.5 K and 2.0 K at Tsukuba campus of KEK. He has received his Ph.D. at the University of Tsukuba, Japan, for the study on superfluid helium flow through porous medium.