Göttingen 2012 – scientific programme
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T: Fachverband Teilchenphysik
T 80: Beschleunigerphysik 2
T 80.6: Talk
Monday, February 27, 2012, 18:00–18:15, VG 1.104
Influence of BCP treatments on roughness and field emission from Nb — •Stefan Lagotzky1, Aliaksandr Navitski1, Günter Müller1, and Peter Kneisel2 — 1University of Wuppertal, D-42097 Wuppertal, Germany — 2TJNAF, VA 23606 Newport News, USA
Enhanced field emission (EFE) from particulate contaminations and surface irregularities is one of the field limitations of the high gradient superconducting Nb cavities required for XFEL and ILC. While the number density and size of particulates can be much reduced by high pressure water rinsing (HPR), dry ice cleaning, and clean room assembly, the optimum choice of the Nb crystallinity and polishing are still under discussion [1]. Moreover, for the actual XFEL cavities two different schemes are used, i.e. "Final EP" and "BCP Flash." The influence of such preparation methods on EFE, however, has been less studied yet. Therefore, we have systematically measured the surface roughness of single-crystal Nb as function of the removed damage layer with BCP (d=20, 40, 80, 120 μm) by means of optical profilometry and AFM. Different measures for the surface roughness, i.e. average and rms roughness, power spectral density, and 2D discrete Fourier transform were used. Correlated EFE and SEM investigations on these samples after HPR have identified surface irregularities as main emitter type. The activated onset fields shift from 80 MV/m (d=20 μm) to 180 MV/m (d=120 μm) in accordance to the roughness.
[1] Reschke et al., Phys. Rev. ST Accel. Beams 13, 071001-1 (2010).
Acknowledgements to D. Reschke and J. Ziegler at DESY for HPR;
fundings by HGF Alliance and the BMBF project 05H09PX5.