The Joint Accelerator Conferences Website (JACoW) is an international collaboration that publishes the proceedings of accelerator conferences held around the world.
TY - CPAPER AU - Lagotzky, S. AU - Müller, G. TI - Field Emission From a Thermally Oxidized Nb Sample J2 - Proc. of International Conference on RF Superconductivity (SRF2015), Whistler, BC, Canada, Sept. 13-18, 2015 AB - Enhanced field emission (EFE) from particulates and surface defects is one of the main field limitations of superconducting Nb cavities required for XFEL and ILC. The activation field Eact of such emitters and the emitter number density N at a given Eact is strongly influenced by the thickness of the Nb oxide layer*. Combination of this effect with surface cleaning techniques, e.g. dry ice cleaning (DIC), potentially shifts the onset of EFE to even higher Eact. Therefore, we have started to investigate a single crystal Nb sample after thermal oxidation (TO) by a heat treatment (HT) in air (T = 360°C, t = 40 min). Field emission maps showed a first emitter at 100 MV/m, and N = 30/cm² at 225 MV/m. SEM analysis of the 10 strongest emitters revealed mainly surface defects and one particulate. Subsequent removal of the oxide by a HT (T = 400°C, t = 1 h) under UHV resulted in an EFE onset at 75 MV/m and increased N to 60/cm² at 225 MV/m. In a second step the TO as well as the measurement was repeated after DIC of the surface. The resulting field maps and the SEM analysis of selected emitters will be reported. PB - JACoW CY - Geneva, Switzerland SP - 233 EP - 236 KW - site KW - vacuum KW - collider KW - linear-collider KW - high-voltage DA - 2015/12 PY - 2015 SN - 978-3-95450-178-6 DO - 10.18429/JACoW-SRF2015-MOPB058 UR - http://srf2015.vrws.de/papers/mopb058.pdf ER -