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@PHDTHESIS{Tamashevich:317338,
      author       = {Tamashevich, Yegor},
      othercontributors = {Elsen, Eckhard and Foster, Brian},
      title        = {{D}iagnostics and treatment of 1.3 {GH}z {N}b cavities},
      issn         = {1435-8085},
      school       = {Universität Hamburg},
      type         = {Dissertation},
      address      = {Hamburg},
      publisher    = {Verlag Deutsches Elektronen-Synchrotron},
      reportid     = {PUBDB-2017-00617, DESY-THESIS-2017-001},
      series       = {DESY-THESIS},
      pages        = {207},
      year         = {2017},
      note         = {Dissertation, Universität Hamburg, 2016},
      abstract     = {The European XFEL and the International Linear Collider are
                      based on superconductingrf cavities. In order to reach the
                      theoretical gradient limits of the superconducting
                      cavitiesit is necessary to increase the mechanical quality
                      and chemical composition of the innersurface as well as to
                      understand the reason for performance limitations. This work
                      is basedon the diagnosis of over 100 XFEL and HiGrade
                      cavities whose performance was limitedby several factors:
                      eld emission on dust or surface defects, low-eld thermal
                      breakdowncaused by the defects, Q-slope etc.It was found
                      that some defects were produced during the mechanical
                      production of thecavity and were not removed by
                      electro-chemical polishing, a standard processing tech-nique
                      of the inner cavity surface. On the other hand, some of the
                      defects were producedduring the electro-chemical polishing
                      process as the surface initially had imperfections
                      orinclusions of foreign material.One of the opportunities to
                      overcome the aforementioned drawbacks is to replace
                      $the\bulk"$ electro-chemical polishing process by mechanical
                      centrifugal barrel polishing. Theparameters of the surface
                      after each polishing step were studied using small samples,
                      so-called coupons. An undersurface layer was investigated
                      using metallographic techniquesand cross sectioning. The
                      inuence of centrifugal polishing on the specic parameters
                      ofa 9-cell cavity (eld atness, eccentricity etc.) was
                      investigated. As a result, a single-stepcentrifugal barrel
                      polishing process followed by a standard $\light"$
                      electropolishing wasproposed for industrial
                      application.Although the performance-limiting mechanisms are
                      understood in general, the origin ofthe quench of the cavity
                      is often unclear. To determine the quench locations, a
                      localisationtool for thermal breakdown using the $\second$
                      sound" in superuid helium has been used.All components of
                      this tool were improved to increase the accuracy of the
                      measurements.A new program code for quench localisation
                      calculating the path of the second-soundwave was developed.
                      This allows the signals from all sensors to be used,
                      regardlessof their position relative to the quench site. The
                      new approach was validated usingadditional techniques such
                      as a temperature mapping and an optical inspection of
                      theinner cavity surface. Furthermore, a new multi-sensor for
                      second-sound wave detection inthe helium vessel of a cavity
                      was developed and successfully tested on a
                      serial-productionXFEL cavity. The determined quench site
                      location was conrmed by subsequent opticalinspection. The
                      algorithm localises the quench without mode measurements
                      i.e. thereis no need to dismount HOM-antennas which requires
                      special procedures and must beperformed in a clean-room.The
                      mathematical approach described in this paper can be applied
                      for second-sound testsof superconductive cavities of various
                      shapes and dimensions.},
      cin          = {FLA},
      cid          = {I:(DE-H253)FLA-20120731},
      pnm          = {611 - Fundamental Particles and Forces (POF3-611)},
      pid          = {G:(DE-HGF)POF3-611},
      experiment   = {EXP:(DE-H253)ILC(machine)-20150101},
      typ          = {PUB:(DE-HGF)3 / PUB:(DE-HGF)29 / PUB:(DE-HGF)11},
      doi          = {10.3204/PUBDB-2017-00617},
      url          = {https://bib-pubdb1.desy.de/record/317338},
}