4.4 and 8 MW two stage DC thyristor power converter with low ripple and drift for high magnetic field research

For research at high magnetic fields (>30 T) a series connection of a superconducting and resistive magnet is used, requiring high DC power (8 MW) with an extremely low current ripple (<; 15 ppm) and a very high short time current stability (2 ppm of In). One single initially 4.4 MW, finally 8 MW, water-cooled thyristor converter with passive filtering is constructed and put in operation, fulfilling all demands. The 8 MW will only be operative when the load circuit will be upgraded. But the DC power supply system is ready for this future load magnet. The power supply system is fed from the public mains putting constraints on the loading thereof. The power converter will be described and design choices explained. The set-up of the control loops will be discussed and some test results presented.