Author: Grassellino, A.
Paper Title Page
WEPPC115 High Q0 in Superconducting Niobium Cavities: Progress at FNAL and Future Plans 2492
  • A. Grassellino, L.D. Cooley, C.M. Ginsburg, A. Romanenko, A.M. Rowe, V.P. Yakovlev
    Fermilab, Batavia, USA
  Consistent improvement in the quality factors of SRF cavities at medium surface fields of about 70 mT represents a direct cost savings factor for the proposed Project X CW linac and other SRF accelerator projects based on CW operation. Current state-of-the-art in SRF does not provide processing recipes to maximize the Q0 at those fields since a complete understanding of the mechanisms governing the quality factor at non-negligible surface fields is not yet developed. In this contribution we present results of the FNAL effort in both scientific understanding and practical improvements and discuss the directions we are pursuing for future research.  
WEPPC116 Depth Distribution of Losses in Superconducting Niobium Cavities 2495
  • A. Romanenko, A. Grassellino, J.P. Ozelis
    Fermilab, Batavia, USA
  • H. Padamsee
    CLASSE, Ithaca, New York, USA
  In order to optimize performances of superconducting niobium cavities it is crucial to understand the structure of near-surface few tens of nanometers of the material. In particular, superconducting properties of niobium, which depend on the presence of impurities and/or defects, may be non-uniform in the magnetic field penetration depth. A few cavity experiments based on oxypolishing* and anodizing**,*** provided some insight into the problem, but the definitive understanding is not developed yet. In this contribution we report on the "depth profiling" of the near-surface RF layer using an alternative technique based on the hydrofluoric acid (HF) rinsing. Tumbled, electropolished and buffered chemical polished cavities have been investigated and tentative nanostructural interpretation is discussed.
* P. Kneisel, Proc. of the 1999 SRF Workshop, Santa Fe, USA
** G. Eremeev and H. Padamsee, Physica C 441 No. 1-2 (2006) 62
*** G. Ciovati, P. Kneisel and A. Gurevich, PRSTAB 10 (2007) 062002