Design and operational aspects of a bi-polar semi-conductor switch as possible candidate for replacement of electro-mechanical switchgear in energy extraction systems for the LHC corrector magnet circuits

More than 600 DC opening switches assure the role of energy extraction in the powering circuits of the bipolar, superconducting beam corrector magnet chains in the LHC collider at CERN. Although the operational experience from several years of extensive use has proven the high reliability of the electro-mechanical breakers, their relatively high need for regular, preventive maintenance and subtle adjustments as well as their limited lifetime has stimulated the interest in considering alternative solutions. The paper presents the development and operational performance details of a prototype, 1 kA, bipolar extraction switch based on back-to-back IGCT's with blocking diodes. The specific features related to the zero-current passing are described and quantified. The associated difficulties for the controls of a powering system to assure the necessary current stability at the transitory points are analyzed, considering the requirements from the beam dynamics. Parameters of various solutions are described in details.