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Zhao, X.

Paper Title Page
WE5PFP062 Surface Topography of "Hotspot" Regions from a Single Cell SRF Cavity 2147
 
  • X. Zhao, G. Ciovati, C.E. Reece, A.T. Wu
    JLAB, Newport News, Virginia
  
 

Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177.


SRF cavities are observed to be limited by non-linear localized effects. The variation of local material parameters between "hot" and "cold" spots is thus of intense interest. Such locations were identified in a BCP etched large-grain single-cell cavity and removed for examination by high resolution electron microscopy (SEM), electron-back scattering diffraction microscopy (EBSD), and scanning Auger electron spectroscopy (SAM). Pits with clear crystal facets were observed on both "Hotspot" and "Coldspot" specimens. The pits were found in-grain and on "Y"-shaped junction of three crystals. They are interpreted as etch pits induced by surface crystal defects (e.g., dislocations). All "Coldspots" examined had obvious low density of etching pits or very shallow tri-crystal boundary junction. EBSD revealed crystal structure surrounding the pits via crystal phase orientation mapping. This study suggests a mechanism by which BCP etching creates pits on large-grain Nb cavity surfaces and sharp-edged topography in fine-grain Nb. Field enhancements at very deep, sharp and densely populated etching pits may then cause distributed hotspots and limit cavity performance.

  
MO6PFP040 Design Study of Combined Magnet with Combined Function Method 226
 
  • X. Zhao, G. Feng, W. Li, L. Wang, H. Xu, S.C. Zhang
    USTC/NSRL, Hefei, Anhui
  
 

HALS(Hefei Advanced Light Source) is the electron storage ring of ultra-low emittance in process of design. Under this design, the quadrupole magnet with sextupole component must be mounted on which the βη is much bigger, to use enough the effect of compersation chromaticity of sextupole magnet field and to use sparingly the space in the same time . So the combined quadrupole and sextupole magnet must be designed, and have more strong sextupole component and restrain the production of high harmonic field. In this paper, the chocie of design scheme is discussed, and the calculation of combined quadrupole and sextupole mangnet design is given.