Division of accelerators, cryogenics and magnetism

Status of Cryogenics for Large Cryogenic Gravity Telescope, KAGRA, N. Kimura

KAGRA is a name of project for Large Cryogenic Gravity Telescope, LCGT, having 3 km base line length in Japan, and was founded by MEXT¹ on FY2010.

The notable characteristic features of KAGARA are a power-recycled Fabry-Perot-Michelson interferometer using mirrors cooled down to 20 K, and placed underground at Kamioka mine. The characteristic design policy of KAGRA is to reduce thermal noise by cryogenic mirror, and escape from thermal lens effect that may reduce the optical power in Fabry-Perot cavities.

 The fundamental technique of cryogenic mirror was developed by a research with Cryogenics Science Center of High Energy Accelerator Research Organization (KEK).

A group in Cryogenics Science Center of KEK grapples with KAGRA cryogenic design, and start production of cryostats with very low vibration cryocooler units under MOU exchanged among KEK, ICRR¹ and NAOJ².  I present the current status of cryogenics design with important R&Ds for KAGRA construction.  

¹) Institute for Cosmic Ray Research (ICRR) of the University of Tokyo    ²) National Astronomical Observatory of Japan    ³) Ministry of Education, Culture, Sport, Science and Technology in Japan

Measurement of helium adsorption on charcoal in cryogenic environment, T. Okamura

From the view point of sub-kelvin cryogenic equipment such as sorption and gas gap heat switch, helium adsorption characteristics on charcoal under cryogenic conditions are introduced. Cryogenic instruments using charcoal such as sorption and gas-gap heat switches play an important role in the field of cosmology and astronomy. In order to develop and fabricate these sub-kelvin cryogenic instruments using charcoal, it is important to understand helium adsorption characteristics on charcoal under cryogenic conditions. We measured adsorption isotherm of helium on charcoal at T=1.7 K, 4.2 K, 77 K, 300 K.

Numerical simulation of natural convection heat transfer in supercritical helium, T. Okamura

From the view point of thermo fluid mechanics, natural convection heat transfer characteristics on supercritical helium obtained from direct numerical simulation are introduced. Superconducting magnets are often cooled by forced flow helium under the supercritical pressures. It is important to clarify not only forced convection but also natural convection heat transfer because cooling channel may have some kind of dead end such that forced convection does not occur in the cooling channel. In this study, laminar turbulent transition processes in the case of vertical channel system with and without riblet are introduced in order to find the passive turbulent control method which has the possibility of heat transfer enhancement even in the dead end such that forced convection does not occur.