Fundamental R&D - Nb
quenches
Paper Title Page
TUFUA4 New Insights on Nitrogen Doping 347
 
  • D. Bafia, J. Zasadzinski
    IIT, Chicago, Illinois, USA
  • D. Bafia, M. Checchin, A. Grassellino, O.S. Melnychuk, A.S. Romanenko, D.A. Sergatskov
    Fermilab, Batavia, Illinois, USA
 
  This paper covers a systematic study of the quench in nitrogen doped cavities: a cavity was sequentially treated/reset with different N-doping recipes which are known to produce different levels of quench field. Analysis of cavity heating profiles using TMAP are used to gain insight on the origins of quench; new recipes demonstrate the possibility to increase quench fields well beyond 30 MV/m. In addition, a new signature of nitrogen doping is explored, namely, a dip in the superconducting resonant frequency below the normal conducting value just below the critical transition temperature, giving further insights on the mechanisms responsible for the large increase in performance of cavities subject to this surface treatment.  
slides icon Slides TUFUA4 [3.097 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUFUA4  
About • paper received ※ 23 June 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
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TUP061 Gradients of 50 MV/m in TESLA Shaped Cavities via Modified Low Temperature Bake 586
 
  • D. Bafia, J. Zasadzinski
    IIT, Chicago, Illinois, USA
  • D. Bafia, A. Grassellino, O.S. Melnychuk, A.S. Romanenko, Z-H. Sung
    Fermilab, Batavia, Illinois, USA
 
  This paper will discuss the 75/120 C modified low temperature bake capable of giving unprecedented accel-erating gradients of above 50 MV/m for 1.3 GHz TESLA-shaped niobium SRF cavities in CW operation. A bifurca-tion in the Q0 vs Eacc curve is observed after retesting cavities without disassembly in between, yielding per-formance that ranges from exceptional to above state-of-the-art. Atomic Force Microscopy studies on cavity cut-outs gives a possible mechanism responsible for this branching in performance, namely, the dissociation and growth of room temperature niobium nano-hydrides that exist near the RF surface, which are made superconduct-ing only through the proximity effect. In-situ low temper-ature baking of cavity cutouts reveals a dissociation of these room temperature nano-hydrides, which could ex-plain the higher performance of cavities subject to similar in-situ heating in the dewar.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP061  
About • paper received ※ 23 June 2019       paper accepted ※ 03 July 2019       issue date ※ 14 August 2019  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)  
 
TUP062 New Insights in the Quench Mechanisms in Nitrogen Doped Cavities 592
 
  • D. Bafia, J. Zasadzinski
    IIT, Chicago, Illinois, USA
  • D. Bafia, D.J. Bice, A. Grassellino, O.S. Melnychuk, A.S. Romanenko, D.A. Sergatskov
    Fermilab, Batavia, Illinois, USA
  • D. Gonnella
    SLAC, Menlo Park, California, USA
  • A.D. Palczewski
    JLab, Newport News, Virginia, USA
 
  This paper will cover a systematic study of the quench in nitrogen doped cavities: three cavities were sequentially treated/reset with different doping recipes which are known to produce different levels of quench field. Analysis of mean free path and TMAP coupled with sample analysis reveals new insights on the physics of the premature quench in nitrogen doped cavities; new recipes demonstrate the possibility to increase quench fields well beyond 30 MV/m.  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-SRF2019-TUP062  
About • paper received ※ 23 June 2019       paper accepted ※ 02 July 2019       issue date ※ 14 August 2019  
Export • reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)