SRF2011 - List of Authors (Halbritter, J.)

Paper	Title	Page
THPO004	Electro- or Chemical- Polishing and UHV Baking of Superconducting rf Nb Cavities and Q(H) Dependencies	695
	J. Halbritter FZ Karlsruhe, Karlsruhe, Germany
	Standard treatments to achieve excellent high rf power Nb accelerator cavities after machining are electro polishing (EP,>0.050mm), buffered chemical polishing (BCP,~0.01mm), or subsequent ~120°C (>10h) UHV baking (LTB)[1-4]. LFQ and HFQ have been discussed in detail in [2,4], here we concentrate on oxidation and on MFQ described by ΔR(H)=R1\|H/Hc\| + R2(H/Hc)², where R1 is related to hysterics weak link, flux losses and R2 is mainly related to heating [3]. The observed differences between BCP, EP and LTB can be related to differences in Nb2O5/NbOx/Nb interfaces. For example: by BCP oxidation the repeated Nb2O5-crystallite nucleation creates DS, weak links and injects O into larger depth [2] where the weak links strengthen MFQ [1,3]; by EP the repeated Nb2O5-crystallite nucleation is missing and so O sticks to the surface and less DSs and weak links are created resulting in less MFQ [1]; and by LTB at, and adjacent to, Nb surfaces O precipitates enforcing MFQ and LTB, enhancing Hc3 and reducing, e.g. RBCS(T,<15GHz) [1-4]. Depending on details to be discussed these intermingled LTB effects after EP may reduce or enhance R(T,<GHz,<20MeV/m). [1] A.Romanenko et al.,PAC’11 [2] A.S.Dhavale, Symp. Techn.of Nb.,JLAB, Sept.2010 [3] G.Ciovati et al., PhysicaC 441,57(2006) [4] J.Halbritter, SRF09-TUPPO089 (Berlin, 2009),p.450

Paper

Title

Page

Electro- or Chemical- Polishing and UHV Baking of Superconducting rf Nb Cavities and Q(H) Dependencies

695

J. Halbritter
FZ Karlsruhe, Karlsruhe, Germany

Standard treatments to achieve excellent high rf power Nb accelerator cavities after machining are electro polishing (EP,>0.050mm), buffered chemical polishing (BCP,~0.01mm), or subsequent ~120°C (>10h) UHV baking (LTB)[1-4]. LFQ and HFQ have been discussed in detail in [2,4], here we concentrate on oxidation and on MFQ described by ΔR(H)=R1|H/Hc| + R2(H/Hc)², where R1 is related to hysterics weak link, flux losses and R2 is mainly related to heating [3]. The observed differences between BCP, EP and LTB can be related to differences in Nb2O5/NbOx/Nb interfaces. For example: by BCP oxidation the repeated Nb2O5-crystallite nucleation creates DS, weak links and injects O into larger depth [2] where the weak links strengthen MFQ [1,3]; by EP the repeated Nb2O5-crystallite nucleation is missing and so O sticks to the surface and less DSs and weak links are created resulting in less MFQ [1]; and by LTB at, and adjacent to, Nb surfaces O precipitates enforcing MFQ and LTB, enhancing Hc3 and reducing, e.g. RBCS(T,<15GHz) [1-4]. Depending on details to be discussed these intermingled LTB effects after EP may reduce or enhance R(T,<GHz,<20MeV/m).
[1] A.Romanenko et al.,PAC’11
[2] A.S.Dhavale, Symp. Techn.of Nb.,JLAB, Sept.2010
[3] G.Ciovati et al., PhysicaC 441,57(2006)
[4] J.Halbritter, SRF09-TUPPO089 (Berlin, 2009),p.450