Breakdown localisation in a pulsed DC electrode system

Breakdown localisation is an important diagnostic for studies of vacuum arcs in high electromagnetic field systems such as DC electrodes and radio frequency (RF) accelerating structures. For example, determining the position of individual breakdowns and corresponding distributions of ensembles of breakdowns are important measurements in high-gradient X-band test stands (CERN, SLAC, KEK) where these measurements are made by monitoring the RF signals. A highly precise breakdown localisation technique has been developed for the CLIC (Compact LInear Collider) pulsed DC electrode systems. These systems are part of the CLIC high-gradient development programme and complementary to RF tests. The optical-based technique discussed here determines where the discharges have occurred by triangulating the emitted light from the breakdown and operates on a breakdown-by-breakdown basis. The implementation of breakdown localisation technique together with a fast Data Acquisition (DAQ) system provides a powerful method of studying breakdown phenomena. The experimental apparatus and its capabilities are presented.