TESTING OF HIGH-CURRENT BYPASS DIODES FOR THE LHC MAGNET QUENCH PROTECTION

Within the framework of the Large Hadron Collider (LHC) R&D programme, CERN is performing experiments to establish the current carrying capa bility of irradiated diodes at liquid Helium temperatures for the supe rconducting magnet protection. Even if the diodes are degraded by radi ation dose and neutron fluence, they must be able to support the by-pa ss current during a magnet quench and the de-excitation of the superco nducting magnet ring. During this discharge, the current in the diode reaches a maximum value up to 13 kA and decreases with an exponential time constant of 100 s. Two sets of 75 mm wafer diameter epitaxial dio des, one irradiated and one non-irradiated, were submitted to this exp eriment. The irradiated diodes have been exposed to radiation in the a ccelerator environment up to 20 kGy and then annealed at room temperat ure. After the radiation exposure the diodes had shown a degradation o f forward voltage of 50 % which reduced to about 14 % after the therma l annealing. During the long duration high current tests, one of the d iodes was destroyed and the other two irradiated diodes showed a diffe rent behaviour compared with non-irradiated diodes.