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VA: Vakuumphysik und Vakuumtechnik

VA 4: Große Vakuumsysteme UHV XHV

VA 4.4: Talk

Tuesday, March 18, 1997, 11:40–12:00, ZH

Particulate Contamination: A Problem which limits the Performances of UHV Systems — •M. Jimenez — LHC Division, CERN, Geneva

Most projects using UHV systems are concerned by particulate contamination which may limit the performaces multipactor, quenches, electron field emission or light diffusion. Up to now, we have been looking for procedures to avoid direct contamination of the surfaces by particles. These particles originate from two different sources: (I) particles already existing and stuck to the surface released, after vibrations induced by sliding or rolling friction and (II) particles generated in-situ by abrasion of the surface. Three types of protection systems have been tested on a UHV sytem: a clean-room tent, a class-100 clean-room and a “dynamical confinement” method which consists in maintaining a clean air-flow through the aperture to be protected in order to repulse the particles outside the critical area. Contamination coming from the first source can be reduced by using clean-room conditions to decrease the number of particles on the surfaces. As for contamination by particles generated in-situ, only the dynamical confinement can reduce the level of contamination. A flow with the speed of around 1.5 m/s is required to minimise the contamination instead of 0.3 m/s recommended by semiconductor manufacturers since the particles generated in-situ in UHV systems have a larger size and density in comparison with particles identified in semiconductor clean-rooms.