DESY, Hamburg
About 50 nine-cell cavities of the recent fine-grain niobium cavity productions have been analysed with respect to maximum gradient and critical field emission onset in the first and final vertical acceptance test, respectively. Parameters of the analysis were the manufacturer of the cavities, the location of the main EP (=> industry or in-house), the final surface treatment (=> final 40μm EP or short 10μm "flash" BCP) and the cavity preparation strategy (=> vertical acceptance test with or without He-Tank welded). Moreover the effect of a re-processing of field emission loaded cavities by additional ultra pure high pressure water rinsing has been investigated.
INFN/LASA, Segrate (MI)
DESY, Hamburg
The tuning system for XFEL SRF cavities is a device based on a double lever driven by a stepping motor with a gear box and a screw-nut system. The cavity is stretched by the tuner thus changing its resonant frequency. The tuner is also provided with fast tuning capability by means of two piezoceramic actuators, that compensate for cavity deformations that are responsible of frequency detuning. During industrial phase is mandatory to ensure a correct tuner assembling both for mechanical parts and actuators. This is provided by an automated device able to check the correctness of piezo-tuner installation on the cold mass string first and after installation in the cryostat, with very simple mounting requirements for the Module Assembling Team. In this paper this device is fully described, and first results on prototypes are shown together with its operation strategy.
DESY, Hamburg
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. Operation can be 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.