Overview and Status of Commissioning of the Wendelstein 7-X Magnet Power Supplies

There are three main magnet systems in Wendelstein 7-X (W7-X), comprising in total 85 coils arranged in 22 independent circuits fed by steady-state power supplies. The superconducting coil system creates the main magnetic field and consists of 70 coils, grouped in 7 electrical circuits with 10 coils each with an inductance of ~1 H. Each circuit is fed by one power supply with a maximum current of 20 kA and a maximum voltage of ±30 V. The second coil system is the so-called trim coil system, intended for enhanced experimental flexibility and error field corrections. It consists of five independently powered copper coils that are placed on the outer side of the cryostat. They will be operated with the currents of up to 1.95 kA. The full-scale ratings of a power supply are ±2200 A(dc) and ±230 V(dc). The third magnet system is the divertor control coil system. The ten normal conducting copper coils are situated inside the plasma vessel behind the divertor targets and are arranged in ten independent circuits. The current rating of one power supply is a dc current of up to ±2500 A, which can be modulated by an ac current of up to 625 A with the frequencies of up to 20 Hz. The commissioning of all the systems was made first by using dummy loads, and finally with the installed coils in W7-X. The final commissioning has been running since November 2014 and will be completed in Summer 2015.