Challenges for the Wendelstein 7-X Magnet Systems During the Next Operation Phase

• Published in: IEEE transactions on plasma science Vol. 46; no. 5; pp. 1517 - 1521
• Main Authors: Rummel, Thomas, Risse, Konrad, Nagel, Michael, Monnich, Thomas, Fullenbach, Frank, Bosch, Hans-Stephan
• Format: Journal Article
• Language: English
• Published: IEEE 01.05.2018
• Subjects: Discharges (electric); Heating systems; Magnetic circuits; Magnetomechanical effects; Operating systems; Plasmas; Resistors; stellarators; Superconducting magnets; Wendelstein 7-X (W7-X)
• ISSN: 0093-3813; 1939-9375
• DOI: 10.1109/TPS.2018.2816399

During the first operation phase OP1.1 of Wendelstein 7-X, the magnet systems were not operated up to its maximum capabilities. During the next operation phase OP1.2, a big step in the direction to a full current operation will be taken. The superconducting magnet system consists of the two different coil types: the nonplanar coils (NPCs) and the planar coils (PLCs). With respect to OP1.1, the NPC current in OP1.2 will be increased slightly, but will be doubled in the PLC. Also a reversal of the current direction in the PLC will be required. Tests during and after OP1.1 showed that it might be advantageous to reduce the electrical stress during fast discharges. Therefore, the magnet protection system was optimized. In order to avoid the risk of a quench, the magnet system is being operated with a certain temperature margin with respect to the critical temperature of the superconductor. The safety operation system will be updated to secure automatic observation and reaction. The five trim coils are normal conducting coils mounted at the outer surface of the cryostat. They were operated during OP1.1 up to 2/3 of the maximum current. Therefore, full current operation needs to be tested for the first time. For OP1.2, also measures were studied and installed to minimize the cross-link between the trim coils and the superconducting main field coils.