Bonn 2010 – wissenschaftliches Programm
HK 8.7: Vortrag
Montag, 15. März 2010, 18:25–18:40, HG ÜR 4
Surface roughness and correlated enhanced field emission investigations of electropolished niobium samples — •Aliaksandr Navitski1, Stefan Lagotzky1, Günter Müller1, Detlef Reschke2, and Xenia Singer2 — 1University of Wuppertal, D-42097 Wuppertal, Germany — 2DESY, D-22603 Hamburg, Germany
Enhanced field emission (EFE) from particulate contaminations or surface irregularities is one of the main field limitations of the high gradient superconducting niobium cavities required for XFEL and ILC . While the number density and size of particulates on metal surfaces can be much reduced by high pressure water rinsing, dry ice cleaning  and clean room assembly of the accelerator modules, the influence of surface defects of the actually electropolished and electron-beam-welded Nb surfaces on EFE has been less studied yet. Therefore, we have systematically measured the surface roughness of typically prepared Nb samples some of which were cut out of a nine-cell cavity by means of optical profilometry and AFM. Pits with crater-like centers and sharp rims as well as scratch-like protrusions were found even on mirror-like surfaces. In order to find correlation between expected EFE and geometry of the defects, field emission scanning microscopy (FESM) and high resolution SEM have been performed on selected samples after HPR at DESY. Impact of the defects on field limitations of cavities will be discussed.  A. Dangwal et al., Phys. Rev. ST Accel. Beams 12, 023501 (2009).  A. Dangwal et al., J. Appl. Phys. 102, 044903 (2007).