Speaker
Michael Nagel
(Wendelstein 7-X Operation)
Description
The first cool down of the stellarator fusion experiment Wendelstein 7-X was achieved within 4 weeks in March 2015. A helium refrigerator with a cooling power of 7 kW at 4.5 K was used to cool down 456 tons of cold mass. The Outer Vessel (OV) of the cryostat contains 70 superconducting coils that are threaded over the twisted Plasma Vessel (PV). These coils are attached to a massive support structure. Both, coils and structure are cooled down to 4 - 5 K. 14 high temperature superconducting current leads connect the warm power cables to the cold superconducting bus bars which are joined with the coil terminals. Heat radiation from the warm surfaces to the cold structures is prevented by a thermal radiation shield around the PV, the OV and 254 ports. The ports allow access to the PV from outside the cryostat and contain supply/return lines and plasma diagnostics. More than 1200 temperature sensors of different types are attached to cryostat components and give information on the temperature of components.
The paper presents the behavior and the analysis of the cryogenic components inside the cryostat. Heat loads and temperature distribution on the thermal shield are described and compared with design calculations. Heat loads on the cold support structure and on the cold coils system with and without current in the coils are discussed. The impact of loss of cooling for 2 days on coils and structure temperatures is explained and the resulting pressure rise in the helium manifolds over time is presented. The analysis demonstrates that achieved temperatures and measured heat loads allow a safe operation of the superconducting coil system. The cryostat fulfills its requirements.
Co-authors
C.P. Dhard
(Wendelstein 7-X Operation, Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
H. Bau
(Wendelstein 7-X Operation, Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
H.-S. Bosch
(Wendelstein 7-X Operation, Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
K. Risse
(Wendelstein 7-X Operation, Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
Michael Nagel
(Wendelstein 7-X Operation, Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
S. Raatz
(Wendelstein 7-X Operation, Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
T. Rummel
(Wendelstein 7-X Operation, Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
U. Meyer
(Wendelstein 7-X Operation, Max-Planck-Institut für Plasmaphysik, Greifswald, Germany)
