Pulsed HV vacuum breakdown of aluminium and velvet cathodes

Summary form only given. In order to characterize different materials under field emission conditions, an experimental device has been developed. This device is able to reproduce electric field levels similar to the fields present in the injector diode of the AIRIX accelerator or in flash radiographic diodes. A HV generator feeds a vacuum diode with 50 to 200 kV pulse, during about 150 ns. Varying the anode/cathode gap, we can reach almost 1000 kV/cm electric fields. Voltage and current are measured directly in the diode via capacitive and inductive probes. The anode consists in a copper grid so that we can observe the light emission from the breakdown plasma with a high speed ICCD camera. We have used this device to evaluate 3 kinds of new velvets and chose the best one to replace the existing one in the AIRIX injector. Actually the 3 velvets have shown very different behaviors under the same experimental conditions. We have also characterized several surface states of aluminum cathodes in order to find a surface with high breakdown threshold to be used in radiographic diodes. More than 650 kV/cm thresholds were reached with oiled (oil with toluene solvent) or varnished (KF anti flash varnish) cathodes.