SRF2011 - List of Authors (Navitski, A.)

Paper	Title	Page
THPO061	Activation of Field Emitters on Clean Nb Surfaces	869
	A. Navitski, S. Lagotzky, G. Müller Bergische Universität Wuppertal, Wuppertal, Germany D. Reschke, X. Singer DESY, Hamburg, Germany
	Funding: Funded by Helmholtz-Allianz ’Physics at the Terascale’ and das BMBF-Verbundprojekt 05H09PX5. Systematic investigations of the enhanced field emission (EFE) from surface irregularities of typical EP and HPR treated Nb samples revealed an exponential increase of the emitter site density N with the initial onset surface field (Eon = 80-160 MV/m) and a strong activation effect, i.e. the final occurrence of EFE at 2-4 times lower Eon relevant for superconducting XFEL and ILC cavities. Possible explanations for this activation are breakdown across the surface oxide, surface erosion by a local microplasma or de/adsorption effects. Such emitter activation might also be caused by the usual baking or rf power processing of cavities. Therefore, we have started a systematic test series with large-grain Nb samples based on correlated field emission microscopy (FESM) and high-resolution SEM investigations before and after heating at temperatures between 122 and 800°C. As expected, we have obtained slightly (x 2) increased N after baking and strongly (x 10) after heating at 800°C. Moreover, the Eon of the activated emitters is reduced down to 40 MV/m. Most emitters could be identified by SEM as micro-scratches. We will discuss the impact of these results on the EFE of SRF cavities.

Paper

Title

Page

Activation of Field Emitters on Clean Nb Surfaces

869

A. Navitski, S. Lagotzky, G. Müller
Bergische Universität Wuppertal, Wuppertal, Germany
D. Reschke, X. Singer
DESY, Hamburg, Germany

Funding: Funded by Helmholtz-Allianz ’Physics at the Terascale’ and das BMBF-Verbundprojekt 05H09PX5.
Systematic investigations of the enhanced field emission (EFE) from surface irregularities of typical EP and HPR treated Nb samples revealed an exponential increase of the emitter site density N with the initial onset surface field (Eon = 80-160 MV/m) and a strong activation effect, i.e. the final occurrence of EFE at 2-4 times lower Eon relevant for superconducting XFEL and ILC cavities. Possible explanations for this activation are breakdown across the surface oxide, surface erosion by a local microplasma or de/adsorption effects. Such emitter activation might also be caused by the usual baking or rf power processing of cavities. Therefore, we have started a systematic test series with large-grain Nb samples based on correlated field emission microscopy (FESM) and high-resolution SEM investigations before and after heating at temperatures between 122 and 800°C. As expected, we have obtained slightly (x 2) increased N after baking and strongly (x 10) after heating at 800°C. Moreover, the Eon of the activated emitters is reduced down to 40 MV/m. Most emitters could be identified by SEM as micro-scratches. We will discuss the impact of these results on the EFE of SRF cavities.