Author: Grassellino, A.
Paper Title Page
MOPOB20 Enhancement of the Accelerating Gradient in Superconducting Microwave Resonators 113
SUPO08   use link to see paper's listing under its alternate paper code  
 
  • M. Checchin, A. Grassellino, M. Martinello, S. Posen, A. Romanenko
    Fermilab, Batavia, Illinois, USA
  • M. Martinello
    Illinois Institute of Technology, Chicago, Illlinois, USA
  • J. Zasadzinski
    IIT, Chicago, Illinois, USA
  
  The accelerating gradient of superconducting resonators can be enhanced by engineering the thickness of a dirty layer grown at the cavity's rf surface. In this paper the description of the physics behind the accelerating gradient enhancement by meaning of the dirty layer is carried out by solving numerically the the Ginzburg-Landau (GL) equations for the layered system. The calculation shows that the presence of the dirty layer stabilizes the Meissner state up to the lower critical field of the bulk, increasing the maximum accelerating gradient.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-MOPOB20  
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WEB1CO03 Surface Impurity Content Optimization to Maximize Q-factors of Superconducting Resonators 663
SUPO28   use link to see paper's listing under its alternate paper code  
 
  • M. Martinello, M. Checchin, A. Grassellino, O.S. Melnychuk, S. Posen, A. Romanenko, D.A. Sergatskov
    Fermilab, Batavia, Illinois, USA
  • M. Checchin
    Illinois Institute of Technology, Chicago, Illlinois, USA
  • J. Zasadzinski
    IIT, Chicago, Illinois, USA
  
  Quality factor of superconducting radio-frequency (SRF) cavities is degraded whenever magnetic flux is trapped in the cavity walls during the cooldown. In this contribution we study how the trapped flux sensitivity, defined as the trapped flux surface resistance normalized for the amount of trapped flux, depends on the mean free path. A systematic study of a variety of 1.3 GHz cavities with different surface treatments (EP, 120 °C bake and different N-doping) is carried out. A bell shaped trend appears for the range of mean free path studied. Over-doped cavities fall at the maximum of this curve defining the largest values of sensitivity. In addition, we have studied the trend of the BCS surface resistance contribution as a function of mean free path, showing that N-doped cavities follow close to the theoretical minimum. Adding these results together we show that the 2/6 N-doping treatment gives the highest Q-factor values at 2 K and 16 MV/m, as long as the magnetic field fully trapped during the cavity cooldown is lower than 10 mG.  
slides icon Slides WEB1CO03 [4.500 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-NAPAC2016-WEB1CO03  
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THA1IO01
 Progress in High Q SRF cavities development: from Single Cell to Cryomodule  
 
  • A. Grassellino
    Fermilab, Batavia, Illinois, USA
  
  This talk will present the summary of the latest progress in nitrogen doping and magnetic flux reduction strategies, starting from the knowledge of the basic phenomena developed via single cell cavities studies in vertical and horizontal cryogenic dewars and via advanced surface studies of samples, to the implementation in an actual large scale cryomodule. Results of studies of the quality factors as a function of cooldown details though critical temperature for the first LCLS2 prototype cryomodule will be presented.  
slides icon Slides THA1IO01 [14.887 MB]  
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