Vibration stability studies of a superconducting accelerating module quadrupole operating at 4.5 K

A new method for low level low frequency vibration measurements in the cryogenic environment is presented. Commercial moving coil seismometers (geophones) have been used to investigate the mechanical stability of the quadrupole of a third generation (so-called Type-III) FLASH cryomodule (named Module 6) in fully operating conditions. Geophones were able to operate at 4.5 K without any loss of performance, providing nanometer level resolution even in the 1-10 Hz frequency band, region not covered by existing data because of the reduced sensitivity of the cooled piezoelectric accelerometers [1]. A preliminary evaluation of the impact of the refrigeration system and of the high power RF on the vibration level of the quadrupole is also presented. The results are of interest for the design of linear accelerator (linac) cryomodules of the International Linear Collider (ILC) [2] and of the European X-ray Free Electron Laser (XFEL) [3], for which the design is a further evolution of the FLASH Type III.