Ultrafast, Redundant, and Unpolarized DC Energy Extraction Systems for the Protection of Superconducting Magnet Circuits

The article presents a new family of low voltage dc switching energy extraction (EES) systems designed for protection of superconducting magnet circuits at CERN, which is appropriate also in other applications. During normal operation, superconducting magnet circuits can store large amounts of energy in their magnetic fields. In the case of a resistive transition (known as "quench"), this energy may be dangerous as it can lead to high temperatures and voltages, eventually damaging the superconducting magnet coils. To prevent this, the magnetic energy must be extracted and dissipated outside the superconducting windings. For this purpose, dedicated energy absorbers are introduced in the circuit by means of opening of dc switches. For the protection of future superconducting magnet circuits at CERN, direct current switching systems (DCSS) with rated currents of 2000 and 600 A have been developed and qualified. Each DCSS is unpolarized and redundant, i.e., composed of two identical direct current switch (DCS) connected in series. Two methods for the current commutation toward the energy absorber element have been investigated, the first one based on IGBT and the second one based on thyristors. A high-power, inductive-dynamic drive provides the ultrafast opening of the vacuum interrupter in the DCS.