CONTROL OF PARTICLE CONTAMINATION WITH LIQUID AND AIR PARTICLE COUNTERS DURING PREPARATION OF THE TTF 1.3 GHZ RESONATORS

A series of 15 superconducting niobium cavities to be used for the TESLA Test Facility (TTF) was tested at DESY. During the processing of these cavities one part of the activities was to study the feasibility of 25 MV/m acceleration gradients with low fieldemission. During the acceptance tests of the TTF cavities subsequently the standard treatment resulted in cavities with very low electron loading at field gradients above 20 MV/m, while in other resonators strong fieldemission started at low levels. During commissioning of the first TTF module, somtetimes the cavities showed a degradation of the applicable acceleration voltage due to enhanced fieldemission. To find the origin of fieldemission we controlled every step of the assembly, cleaning and preparation procedure in respect to particle contamination due to the process. A liquid particle counter is installed in the HP rinsing stand to control the water draining from the cavity beam-tube as well as the clean-water plant. The assembly procedure of the cavities is monitored with an air particle counter. Investigations in material and material combinations with respect to particles production were done with an air particle counter setup, that allows particle measurements outside and inside of a cavity torus. We report on the set up and commissioning of the liquid particle counter and results obtained from the series of tests and cavity assemblies.