The Conceptual Design of Thermal Shield for KSTAR TOKAMAK System
韓國基礎科學支援研究院, (*)韓國原子力研究所
@金東洛, 許南一, 趙昇衍, 金昇顯, 權 勉, 李京洙, 尹炳周*
The KSTAR(Korea Superconducting Tokamak Advanced Research)Project is in progress since 1996(1). Major parameters of the KSTAR tokamak are : major radius of 1.8m, minor radius of 0.5m, toroidal field of 3.5 Tesla and plasma current of 2MA with a strongly shaped plasma cross-section and double-null diverter. The main purpose of the thermal shield(TS) for KSTAR tokamak is to eliminate the thermal radiation from the room temperature side to the coil temperature(4.5K) region so as to reduce the thermal load on the He refrigerator. There are two types of thermal shields ; one is the vacuum vessel thermal shield (VVTS) located 5 cm off the VV outer wall and the other is the cryostat thermal shield (CTS) located 15 cm off the inside cryostat. Both shields act as heat barriers between superconducting magnets that operate at 4.5 K and the surfaces of cryostat and VV whose temperature is 300 K. The TS is composed of multilayer insulation(MLI) which is the insulating material coated with very thin aluminum on the Mylar, cryopanel which is cooled by cold gaseous He, and supports which stand the cryopanel and MLI on the room temperature part. The thermal shielding cryopanel is cooled under 80 K and 100K during normal operation and bakeout of vacuum vessel, respectively, by a forced flow of 20bar helium gas through cooling pipes on the cryopanel(Table 1). The KSTAR machine is TOKAMAK type and there are strong mechanical loads and vibrations induced by plasma disruption and abrupt sweep of pulsed high magnetic field. The cryopanel must endure these mechanical loads and high pressure of cooling gas. Currently considering cryopanel types are; double wall type, serpentine type and spot-welded cryopanel and to be selected the proper one for its condition. In this work current status of the design of thermal shield will be mentioned.