J.Y. Lim, K.H Chung, Y.H. Shin, and S.S. Hong
Korea Research Institute of Standards and Science, Taejon 305-600, Korea
J. Kim
Korea Basic Science Institute, Taejon 305-333, Korea
L. Sevier
General Atomics, P.O. Box 85608, San Diego, CA 92186
The Korea Superconducting Tokamak Advanced Research (KSTAR) tokamak device is capable of a long pulse (up to 300s) plasma operation utilizing superconducting coils with a cryostat boundary. Its well-designed integrated vacuum pumping system including torus, cryostat, NBI, and diagnostics pumping subsystems is essential to achieve the physics requirements set in the Physics Requirements Document (PRD) for the optimized plasma performance and continuous operation. The primary goal of the pumping system is maintaining the appropriate pressures in torus vacuum vessel during various operational modes: plasma discharge, glow discharge cleaning, vacuum vessel bake-out, and regeneration of the in-vessel cryocondensation pump.
A trade study has been performed to assess the performance of the two pumping duct geometries, bottom vertical ports and NBI ports. The device and facility will be able to provide high vacuum conditions with a base partial pressure of 1 x 10-7 torr for fuel gases (Z 2) and a base partial pressure of 1 x 10-9 torr for impurity gases (Z>2). A projected outgassing rate (<1 x 10-9 W/m2) with suitable cleaning, leak detection, and conditioning techniques will satisfy the impurity gas load limit (1 x 10-5 torr-l/s) as well.
Typical and optimum operating pressure regimes of the cryostat and of the vacuum vessel are studied and set to 5 x 10-6 torr for the cryostat vacuum environment to limit the thermal loads applied to the superconducting magnet system, 1 to 3 x 10-3 torr for torus glow discharge cleaning and regeneration of the in-vessel cryocondensation pump, low 10-6 torr range during plasma discharge, and low 10-9 torr range for maintaining cleanliness during baking and standby mode. The integrated KSTAR pumping system schematics as well as a graphical operation scenario of the pumping system will be incorporated in the plasma operation, cryostat and torus pumping, in-vessel cryopumping, and glow discharge schemes.
*Work supported by the Ministry of Science and Technology of the Republic of Korea