Pierre Briend

DESIGN AND MANUFACTURING OF THE KSTAR TOKAMAK HELIUM REFRIGERATION SYSTEM

The KSTAR (Korean Superconducting Tokamak Advanced Research) project makes intensive use of superconducting (SC) magnets operated at 4.4 K. The cold components of KSTAR require a forced flow of supercritical helium for magnets and structure, boiling liquid helium for current leads, and gaseous helium for thermal shields. A helium refrigeration system has been custom-designed for this project. The purpose of this paper is to give a brief overview of the proposed cryogenic system. The specified thermal loads for the different operating modes are presented. This specification results in the definition of a design mode for the refrigerator. The design and construction of the resulting 9 kW at 4.5-K Helium Refrigeration System (HSR) are presented.

Design issues of the distribution valve box of the KSTAR helium refrigerator

Publisher Summary This chapter reports the design issues of the Korea Advanced Superconducting Tokamak Research (KSTAR). The operation mode of the KSTAR helium refrigerator is based on the day average thermal load of the KSTAR cold components. Because the thermal load on the magnets and current-feeding devices of KSTAR are strongly time-dependent, a system which smoothens the heat load peaks and distributes the cryogenic helium at the proper instant is required. The design issues of such a system, the distribution valve box of the KSTAR helium refrigerator, which are essential to cope with various operation modes and probable abnormal events of the KSTAR device have also been discussed in the chapter. The major task of the DV box of the KSTAR helium refrigerator is the distribution of helium during various normal operation modes and the cool-down/warm-up of the cold components of KSTAR. However, by installing proper valves, heaters, and by-pass lines to the helium circuit of the DV box, it is possible to perform other tasks, such as CICC cleaning, protection of KSTAR and the refrigerator in case of abnormal events, and the pre-commissioning of the refrigerator by simulating the time variation of the thermal load and pressure in each cold component of KSTAR before being connected to the refrigerator.

Two Large 18 KW (Equivalent Power at 4.5 K) Helium Refrigerators for Cern’s LHC Project, Supplied by Air Liquide

CERN in Switzerland has decided to build a new accelerator project called LHC (Large Hadron Collider). This 27 km long accelerator will, for the first time at a such large scale, operate superconducting magnets and radiofrequency cavities. For that purpose Air Liquide is now building two custom designed refrigerators of cryogenic power 18 kW equivalent at 4.5 K. The thermodynamical cycle, chosen to fit the LHC cryogenic loads with a very high efficiency, is discussed. A special emphasis is put on the cold end that makes use of a cryogenic expansion turbine discharging into the double phase domain. As these refrigerators are designed to be able to be operated at reduced cryogenic power with reduced electrical power consumption, chosen solutions to adapt the refrigerator operation to reduced load are described.

Air liquide cryogenic system for the KSTAR device

Publisher Summary This chapter gives a brief overview of the proposed cryogenic system for the KSTAR tokamak and begins by quantifying the thermal loads of the refrigerator in the normal modes of operation and by describing the thermo-dynamical and process approach leading to the refrigerator design power. The cold components of the KSTAR tokamak require forced flow of supercritical helium for magnets/structure, boiling liquid helium for current leads, and gaseous helium for thermal shields. The cryogenic system is designed to provide stable operation and full automatic control. A three-pressure helium cycle composed of six turbines has been simulated. A design operating mode has been selected using an exergy approach. The result is a 7 kW constant power refrigerator and the use of gas and liquid storages for mass balance. The time-dependent heat load deposit from the tokamak during Shot/Standby mode is buffered into a thermal damper. A flow control method is proposed, which will allow a very stable operation of the refrigerator.

Design of cryogenic system for the KSTAR device

Publisher Summary This chapter describes the development of the cryogenic system for the KSTAR tokamak device. The device requires a large amount of refrigeration power at several temperature levels. The design of the KSTAR helium refrigeration system is based on the refrigerator and distribution system. The helium refrigerator is designed to operate stably to cope with the pulse heat loads of the superconducting magnet operation in tokamak device. The helium distribution system is designed to distribute refrigeration to KSTAR cooling components such as 30 superconducting coils, magnet supporting structures, thermal shields, and current leads with a minimal temperature variation. The static and pulse heat loss of the KSTAR cold components is estimated. The main design feature for the KSTAR helium refrigerator is peak power save system by using the thermal damper and LHe storage tank because the KSTAR tokamak is a pulse-operated device. The typical day average heat losses of each device are 1.7 kW at 4.5 K of supercritical helium, 13 kW at 70 K of gaseous helium, and 13 g/s of liquid helium.