The vacuum arc is a well-known technique for producing coatings with enhanced adhesion and film density. Many cathodic arc deposition systems are actually in use in industry and research. They all work under (high) vacuum conditions in which water vapour pressure is an important source of film contamination, especially in the pulsed arc mode of operation. Here we present a cathodic arc system working under ultra-high vacuum conditions (UHVCA). We have used for arc ignition a Nd-YAG pulsed laser focused on the cathode surface, which provides a reliable system and allows eliminating all possible sources of contaminants. We have proven that the arc technique produces bulk-like films suitable for superconducting applications. UHVCA has been used to produce ultra-pure niobium films with excellent structural and electrical properties at a deposition temperature lower than 100oC. The UHVCA technique therefore opens up new perspectives for all applications requiring pure films and low deposition temperatures.
We discuss the progress in the R&D program for a future upgrade of the European XFEL facility, namely for an operation in the continuous wave (cw) and long pulse (lp) modes, which will allow for significantly more flexibility in the electron and photon beam time structure. Results of cw/lp runs with preseries XFEL cryomodules and status of components needed for the new operation modes are presented here.
Abstract—Niobium thin film coated copper RF cavities are an\ud
interesting alternative to niobium bulk cavities for the development\ud
of high performance superconducting accelerators. The\ud
main limiting factor in their use is the degradation of the quality\ud
factor Q with increasing accelerating field (the “Q-Slope”). To try\ud
and overcome this limitation, we have developed an alternative\ud
coating technique based on a Cathodic Arc system working under\ud
UHV conditions (UHVCA). High quality Nb samples have been\ud
synthesized under different deposition angles and their characteristics\ud
are presented. The UHVCA technique has been used to\ud
deposit 1.3 GHz TESLA-type single cell cavities. To further improve\ud
cavity performance the first critical field has to be enhanced.\ud
The use of multilayers consisting of alternating insulating and\ud
superconducting layers may produce the desired enhancement\ud
providing that the superconducting layer thickness is smaller than\ud
the London penetration depth. To this aim, we present also the\ud
experimental characterization of the superconducting properties of Nb/AlOx/Nb multilayer
After three years of preparation, two superstructures, each made of two superconducting 7-cell weakly coupled subunits, have been installed in the TESLA Test Facility linac (TTF) for the cold-and beam test. The energy stability, the HOMs damping, the frequency and the field adjustment methods were tested. The measured results confirmed expectation on the superstructure performance and proved that alternative layout for the 800 GeV upgrade of the TESLA collider, as it was proposed in TDR [1], is feasible. We report on the test and give here an overview of its results which are commented in more detail elsewhere in these Proceedings.
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