Pseudo-spark Switch Development For The LHC Beam Dumping System

The kicker magnet pulse generators for the beam dumping system of CERNs Large Hadron Collider (LHC) require fast high power switches (35 kV, 30 kA, 8 ps) of very low repetition rate (only a few pulses per day). Cold cathode tubes like pseudo-spark switches look suitable for this kind of application, as they do not suffer from cathode-heater lifetime limitations and may guarantee a quasi unlimited operation time. Pseudo-spark assemblies are therefore under development with the aim of obtaining a switch tailored to two main requirements of the LHC dumping system, a very low prefire rate (-10-4) and a large ratio of maximum to minimum operation voltage (-15). It is intended to achieve these goals with a 2-gap or 3-gap version employing a ferroelectric trigger in each of the gaps. Experimental results on several 1-gap prototypes of different electrode diameter will be reported. Two of the prototypes have been mounted in a sealed-off version, equipped with a deuterium gas reservoir. The erosion behaviour has been investigated for different electrode materials, pure tungsten, thoriated tungsten and tungstedrhenium (5% Re). Important differences in the quenching behaviour between pure and thoriated tungsten have been found. The incorporation of these results into a 2-gap beam dump switch, soon to be assembled, will be discussed.