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Shu, J. B.

Paper Title Page
WEPMS011 Comparative Surface Studies on Fine-grain and Single Crystal Niobium Using XPS, AES, EBSD and Profilometry 2349
 
  • A. Romanenko, G. V. Eremeev
    CLASSE, Ithaca
  • H. Padamsee, J. B. Shu
    Cornell University, Ithaca, New York
 
  Funding: Supported by NSF

As the surface magnetic field in niobium cavities approaches the theoretical critical field, rf losses begin to grow sensitive to increasingly subtle features of the material and the surface. A striking example is the familiar occurrence of the high-field Q-slope, where rf losses increase exponentially with field above an onset field. A surprising feature of the high-field Q slope is its positive response to mild baking at 120 C. But the Q-slope returns after the first 20 nm of the niobium metal surface is converted to loss-less pentoxide via anodization, a key feature. The latter result suggests that the cause of the fast growing losses resides in the first 20 nm of the rf surface. Although there are several propositions, the exact mechanism for the high-field Q-slope is not yet fully understood and demands further research. We are conducting surface analytic studies with XPS, SIMS, and Auger to shed light on the mechanism of the high-field Q-slope. We are comparing the behavior of fine-grain samples with single crystal samples, BCP treatments with EP treatments and properties before and after 120 C bake. We also study the effect of baking at temperatures up to 400 C.