The successful production and associated vertical testing of over 800 superconducting 1.3 GHz accelerating cavities for the European X-ray Free Electron Laser (XFEL) represents the culmination of over 20 years of superconducting radio-frequency R&D. The cavity production took place at two industrial vendors under the shared responsibility of INFN Milano-LASA and DESY. Average vertical testing rates at DESYexceeded 10 cavities per week, peaking at up to 15 cavities per week. The cavities sent for cryomodule assembly at Commissariat à l'énergie atomique (CEA) Saclay achieved an average maximum gradient of approximately 33 MV=m, reducing to ∼30 MV=m when the operational specifications on quality factor (Q) and field emission were included (the so-called usable gradient). Only 16% of the cavities required an additional surface retreatment to recover their low performance (usable gradient less than 20 MV=m). These cavities were predominantly limited by excessive field emission for which a simple high pressure water rinse (HPR) was sufficient. Approximately 16% of the cavities also received an additional HPR, e.g. due to vacuum problems before or during the tests or other reasons, but these were not directly related to gradient performance. The in-depth statistical analyses presented in this report have revealed several features of the series produced cavities.
Laser-produced plasma sources of short-wavelength (1–20-nm) radiation are actively used nowadays in numerous applications, including water-window microscopy and extreme ultra-violet lithography. Suppression of laser-plasma debris (responsible for damaging optics) is crucial for the lifetime prolongation of optical systems operated with the short-wavelength radiation. Here, we examine the capability of single-walled carbon nanotube (SWCNT)-based membranes to decrease an InSn plasma flux containing both ions and atoms. Faraday cup measurements show that 40- and 90-nm-thick SWCNT membranes reduce the total charge transition by 20 and 130 times, respectively. The ion analyzer measurements demonstrate that ions pass through the membrane mainly due to the collisionless (ballistic) mechanism. Using scanning electron microscopy, we estimate a decrease in a plasma (ions + atoms) flux to be of 18 and 140 times for 40- and 90-nm-thick SWCNT-based membranes, respectively. The average plasma flux attenuation coefficient of SWCNT membranes is calculated as k = 0.063 [Formula: see text].
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