29th Symposium on Fusion Technology (SOFT 2016)

O5C.1 First Operational Phase of the Superconducting Magnet System of Wendelstein 7-X

8 Sep 2016, 16:40

20m

Meeting Hall V 2nd floor (Prague Congress Centre)

Board: 1

Oral E. Magnets and Power Supplies O5C

Speaker

Konrad Risse (W7-X Operation)

Description

The Wendelstein 7-X stellarator (W7-X), one of the largest stellarator fusion experiments, is presently in the first operational phase at the Max Planck Institute for Plasma Physics in Greifswald, Germany. The W7-X shall prove the reactor relevance of the optimized stellarator concept. To confine 30m³3 plasma the W7-X machine has a superconducting magnet system with 50 non-planar and 20 planar coils grouped in five equal modules, electrically connected in seven circuits with 10 coils of each type. The connections between the coils are made by superconducting bus bars using the same NbTi Cable-in-Conduit Conductor as used for the superconducting coils. Specially developed high temperature superconducting current leads feed the current into the cryostat vacuum by bridging the temperature gradient from room temperature down to the 4 K level. Seven power supplies provide individual currents in the seven circuits. The quench detection system checks permanently the superconducting system regarding the occurrence of a quench. In case of a quench, the magnet safety system has to be activated and a set of switches lead the current into dump resistors. The magnet commissioning was successfully performed until mid of 2015 with tests of the complete magnet system functionality needed for plasma operation, at a magnetic field of 2.5 T. The first operational phase started mid of December 2015 with He plasma heated by the ECRH (Electron Cyclotron Resonance Heating) system followed by H2 plasma in January 2016. The superconducting coils and their nonlinear support structure are equipped with a large set of mechanical sensors e.g. strain gauges, contact and distance measuring sensors. For these sensors an online monitoring is established to detect any deviations from the behavior as predicted. The paper will present the experiences from the operation of the superconducting magnets during the first plasma operational phase.