The main goal of the proposed project is to investigate and understand the process of N2- and noble-gas doping of superconducting Nb-cavities for accelerators. The doping will be performed in a high temperature cell suited for in-situ X-ray experiments, especially using X-ray absorption techniques (EXAFS & XANES). Previous results obtained by the applicants have shown that the formation of Nb-nitrides appears rather unlikely, although predicted by several studies in the past. Thus, one main goal of the present project is also to investigate doping by noble gases (i.e. Ar, Kr, Xe) that showed positive effects on the quality factor of the superconducting Nb-cavities. As a negative consequence of any heat treatment, however, parasitic electron field emission (FE) is often observed, and thus the conditions for the activation of those field emitters have to be understood in order to further optimize the cavities. Thus a second main goal of the proposed project is for the first time the parallel and correlated investigation of both the effect of doping and the activation respectively the suppression of FE-activation during heat treatments of Nb. For this purpose, a combination of different techniques such as optical profilometry, atomic force microscopy, scanning electron microscopy, scanning field emission microscopy together with X-ray techniques will be used, and the effects of a subsequent treatment with ion- and laser-annealing will be examined as well.

Duration:
01.07.2018 – 30.06.2021

Project-leader:
Prof. Dr. D. Lützenkirchen-Hecht

Budget:
311.500 €