PARTICLE FREE PUMP DOWN AND VENTING OF UHV VACUUM SYSTEMS

For particle free vacuum systems, as e.g. systems containing superconducting cavities to be operated at high gradients, special care needs to be taken during pump down and venting. Neither should be particles introduced into the vacuum system, nor should particles already present within the system be moved. A series of measurements to study the movement of particles in long tubes during pump down and venting using an in-situ vacuum particle counter has been performed. Based on these measurements a set-up using flow controllers, diffuser and pressure gauges has been developed to avoid introducing particles into the vacuum system as well as moving existing particles during pump down and venting. This set-up can be operated manually as well as via a control unit. The electronics unit is an in-house development at DESY. It is usually connected to an oil free pump station. This set-up allows automated pump-down and venting of critical vacuum systems in a reliable and reproducible way, being faster than the procedures used so far