Author: Lu, X.Y.
Paper Title Page
MOPC117 Advance in Vertical Buffered Electropolishing on Niobium for Particle Accelerators* 352
 
  • A.T. Wu, S. Jin, J.D. Mammosser, C.E. Reece, R.A. Rimmer
    JLAB, Newport News, Virginia, USA
  • L. Lin, X.Y. Lu, K. Zhao
    PKU/IHIP, Beijing, People's Republic of China
  
  Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes.
Nio­bi­um (Nb) is the most pop­u­lar ma­te­ri­al that has been em­ployed for mak­ing su­per­con­duct­ing radio fre­quen­cy (SRF) cav­i­ties to be used in var­i­ous par­ti­cle ac­cel­er­a­tors over the last cou­ple of decades. One of the most im­por­tant steps in fab­ri­cat­ing Nb SRF cav­i­ties is the final chem­i­cal re­moval of 150 μm of Nb from the inner sur­faces of the SRF cav­i­ties. This is usu­al­ly done by ei­ther buffered chem­i­cal pol­ish­ing (BCP) or elec­tropol­ish­ing (EP). Re­cent­ly a new Nb sur­face treat­ment tech­nique called buffered elec­tropol­ish­ing (BEP) has been de­vel­oped at Jef­fer­son Lab. It has been demon­strat­ed that BEP can pro­duce the smoothest sur­face fin­ish on Nb ever re­port­ed in the lit­er­a­ture while re­al­iz­ing a Nb re­moval rate as high as 10 μm/min that is more than 25 and 5 times quick­er than those of EP and BCP(112) re­spec­tive­ly. In this con­tri­bu­tion, re­cent ad­vance in op­ti­miz­ing and un­der­stand­ing BEP treat­ment tech­nique is re­viewed. Lat­est re­sults from RF mea­sure­ments on BEP treat­ed Nb sin­gle cell cav­i­ties by our unique ver­ti­cal pol­ish­ing sys­tem will be re­port­ed.
Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150. 		 
 
MOPC118 Effects of the Thickness of Niobium Surface Oxide Layers on Field Emission* 355
 
  • A.T. Wu, S. Jin, J.D. Mammosser, R.A. Rimmer
    JLAB, Newport News, Virginia, USA
  • X.Y. Lu, K. Zhao
    PKU/IHIP, Beijing, People's Republic of China
  
  Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes.
Field emis­sion on the inner sur­faces of nio­bi­um su­per­con­duct­ing radio fre­quen­cy cav­i­ties is still one of the major ob­sta­cles for reach­ing high ac­cel­er­at­ing gra­di­ents for SRF com­mu­ni­ty. Our pre­vi­ous ex­per­i­men­tal re­sults* seemed to imply that the thresh­old of field emis­sion was re­lat­ed to the thick­ness of Nb sur­face oxide lay­ers. In this con­tri­bu­tion, a more de­tailed study on the in­flu­ences of the sur­face oxide lay­ers on the field emis­sion on Nb sur­faces will be re­port­ed. By an­odiza­tion tech­nique, the thick­ness of the sur­face pen­tox­ide layer was ar­ti­fi­cial­ly fab­ri­cat­ed from 3 nm up to 460 nm. A home-made scan­ning field emis­sion mi­cro­scope was em­ployed to per­form the scans on the sur­faces. Emit­ters were char­ac­ter­ized using a scan­ning elec­tron mi­cro­scope to­geth­er with an en­er­gy dis­per­sive x-ray an­a­lyz­er. The SFEM ex­per­i­men­tal re­sults were an­a­lyzed in terms of sur­face mor­phol­o­gy and oxide thick­ness of Nb sam­ples and chem­i­cal com­po­si­tion and ge­o­graph­ic shape of the emit­ters. A model based on the clas­sic elec­tro­mag­net­ic the­o­ry was de­vel­oped try­ing to un­der­stand the ex­per­i­men­tal re­sults. Pos­si­bly im­pli­ca­tions for Nb SRF cav­i­ty ap­pli­ca­tions from this study will be dis­cussed.
* A.T. Wu et al., Proc. of IPAC 2010, Kyoto, Japan, WEPEC081, p. 3067 (2010).
Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150.
 
 
MOPC119 Fastest Electropolishing Technique on Niobium for Particle Accelerators* 358
 
  • A.T. Wu, S. Jin, R.A. Rimmer
    JLAB, Newport News, Virginia, USA
  • X.Y. Lu, K. Zhao
    PKU/IHIP, Beijing, People's Republic of China
  
  Funding: The U.S. Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce this manuscript for U.S. Government purposes.
Field emis­sion on the inner sur­faces of nio­bi­um (Nb) su­per­con­duct­ing radio fre­quen­cy (SRF) cav­i­ties is still one of the major ob­sta­cles for reach­ing high ac­cel­er­at­ing gra­di­ents for SRF com­mu­ni­ty. Our pre­vi­ous ex­per­i­men­tal re­sults [1] seemed to imply that the thresh­old of field emis­sion was re­lat­ed to the thick­ness of Nb sur­face oxide lay­ers. In this con­tri­bu­tion, a more de­tailed study on the in­flu­ences of the sur­face oxide lay­ers on the field emis­sion on Nb sur­faces will be re­port­ed. By an­odiza­tion tech­nique, the thick­ness of the sur­face pen­tox­ide layer was ar­ti­fi­cial­ly fab­ri­cat­ed from 3nm up to 460nm. A home-made scan­ning field emis­sion mi­cro­scope (SFEM) was em­ployed to per­form the scans on the sur­faces. Emit­ters were char­ac­ter­ized using a scan­ning elec­tron mi­cro­scope to­geth­er with an en­er­gy dis­per­sive x-ray an­a­lyz­er. The ex­per­i­men­tal re­sults could be un­der­stood by a sim­ple model cal­cu­la­tion based on clas­sic elec­tro­mag­net­ic the­o­ry as shown in Ref.1. Pos­si­bly im­pli­ca­tions for Nb SRF cav­i­ty ap­pli­ca­tions from this study will be dis­cussed.
Authored by The Southeastern Universities Research Association, Inc. under U.S. DOE Contract No. DE-AC05-84ER40150. 		 
 
TUPC108 Beam Diagnostics Based on Higher Order Mode for High Repetition Beam 1269
 
  • X. Luo, X.Y. Lu, F. Wang
    PKU/IHIP, Beijing, People's Republic of China
  • F.S. He
    JLAB, Newport News, Virginia, USA
  
  The sig­nals from the HOM ports on su­per­con­duct­ing cav­i­ties can be used as beam po­si­tion mon­i­tors. The HOM am­pli­tude of dipole mode is pro­por­tion­al to the beam off­set. For high rep­e­ti­tion bunch­es op­er­a­tion, the spec­trum is con­sist of the HOMs peaks and the peaks which is in­te­ger times of the bunch rep­e­ti­tion. The HOMs am­pli­tudes should be sep­a­rat­ed from the two kinds of peaks. Based on the sim­u­la­tion from a TESLA 2-cell cav­i­ty, the trans­form ma­trix be­tween the HOMs am­pli­tudes and beam off­sets has been found, as well as the cav­i­ty axis. The sim­u­la­tion re­sults have demon­strat­ed that beam di­ag­nos­tics based on HOMs is fea­si­ble while high rep­e­ti­tion bunch­es op­er­a­tion.