Author: Nishiwaki, M.
Paper Title Page
MOPC092 Effect of Current Densities on Sulfur Generation at Electropolished Niobium Surface 292
 
  • P.V. Tyagi
    Sokendai, Ibaraki, Japan
  • H. Hayano, S. Kato, M. Nishiwaki, T. Noguchi, T. Saeki, M. Sawabe
    KEK, Ibaraki, Japan
  
  We con­duct­ed a se­ries of elec­tropol­ish­ing (EP) ex­per­i­ments in aged EP acid with high (≈50 mA/cm2) and low (≈30 mA/cm2) cur­rent den­si­ties on Nb sur­faces. The ex­per­i­ments were car­ried out both for lab­o­ra­to­ry coupons and a real Nb sin­gle cell cav­i­ty with six wit­ness sam­ples lo­cat­ed at three typ­i­cal po­si­tions (equa­tor, iris and beam pipe). All the sam­ples sur­face were in­ves­ti­gat­ed by XPS (x-ray pho­to­elec­tron spec­troscopy), SEM (scan­ning elec­tron mi­cro­scope) and EDX (en­er­gy dis­per­sive x-ray spec­troscopy). The sur­face anal­y­sis showed the EP with a high cur­rent den­si­ty pro­duced a huge amount sul­fate par­ti­cles at Nb sur­face where­as the EP with a low cur­rent den­si­ty is very help­ful to mit­i­gate sul­fate at Nb sur­face in both the ex­per­i­ments.  
 
MOPC093 Novel Field Emission Scanner for Surface Study of Niobium SRF Cavity 295
 
  • S. Kato, M. Nishiwaki, T. Noguchi
    KEK, Ibaraki, Japan
  • V. Chouhan
    GUAS, Kanagawa, Japan
  • P.V. Tyagi
    Sokendai, Ibaraki, Japan
  
  It is manda­to­ry to in­ves­ti­gate field emis­sion on Nb SRF cav­i­ty sys­tem­at­i­cal­ly since strong field emis­sion often lim­its the cav­i­ty per­for­mance. The field emis­sion strength and the num­ber of emis­sion sites strong­ly de­pend on Nb sur­face prop­er­ties which are de­ter­mined by its sur­face treat­ment and han­dling. Field emis­sion scan­ner (FES) de­vel­oped al­lows us to mea­sure a dis­tri­bu­tion of the field emit­ting sites over a sam­ple sur­face at a given field strength along with its FE-SEM ob­ser­va­tion and en­er­gy dis­per­sive x-ray anal­y­sis. FES con­sists of an anode nee­dle driv­en by pre­cise 3D step­ping mo­tors and an eu­cen­tric sam­ple stage. The com­pact scan­ner was in­stalled into the space be­tween the ob­ject lens and the SEM sam­ple hold­er. In ad­di­tion, this sys­tem was newly equipped with a sam­ple load-lock sys­tem for ex­ist­ing UHV suit­cas­es. There­fore a sam­ple coupon to be ob­served is hard­ly ex­posed to con­tam­i­nants and dust par­ti­cles dur­ing the trans­porta­tion. In-situ heat­ing of a sam­ple coupon can be done dur­ing an ex­per­i­ment to sim­u­late a bak­ing pro­cess of a SRF cav­i­ty. This ar­ti­cle de­scribes de­vel­op­ment of the field emis­sion scan­ner and its pre­lim­i­nary re­sults of the ap­pli­ca­tion to nio­bi­um sam­ples.