• F.S. He, J. Dai, J.K. Hao, S. Jin, Y.M. Li, L. Lin, K.X. Liu, X.Y. Lu, S.W. Quan, W. Xu, B.C. Zhang, K. Zhao, F. Zhu
  PKU/IHIP, Beijing

Peking Uni­ver­si­ty is striv­ing for con­struct­ing a su­per­con­duct­ing ra­dio-fre­quen­cy ac­cel­er­a­tor test fa­cil­i­ty (PKU-SETF) to pro­vide co­her­ent ra­di­a­tions [1]. A cry­omod­ule con­sist­ing of a China made 9-cell TESLA type cav­i­ty was de­signed and con­struct­ed for this pur­pose, which is ex­pect­ed to pro­vide 15-20 MeV en­er­gy gain at an op­er­at­ing tem­per­a­ture of 2K. Some tech­ni­cal is­sues in the man­u­fac­tur­ing progress are re­port­ed, in­clud­ing the tung­sten inert gas (TIG) weld­ing of the LHe ves­sel and the su­per­con­duct­ing cav­i­ty, the de­mag­ne­ti­za­tion of the vac­u­um ves­sel made of pure iron, and the man­u­fac­tur­ing of the main power cou­pler.

• L. Yang
  Peking University, School of Physics, Beijing
• X.Y. Lu
  PKU/IHIP, Beijing

This paper in­tro­duce a pos­si­ble so­lu­tion to im­prove the ef­fi­cien­cy of the very low beta SC ac­cel­er­at­ing struc­ture, via ex­tend­ing the gaps num­ber of 4-gap in­ter­dig­i­tal QWR by dou­bling its stems num­ber. The new cav­i­ty is a 8-gap QWR, which is com­prised of two par­al­lel TEM res­o­nant lines op­er­at­ing in op­pos­ing phase from each other. It main­tains the 4-gap QWR's good EM pa­ram­e­ters and en­ables the use of de­mount­able flange. The more im­por­tant ad­van­tage is the po­ten­tial im­prove­ment of ef­fi­cien­cy. Ac­cord­ing to a pre­lim­i­nary es­ti­ma­tion of lon­gi­tu­di­nal dy­nam­ics, the 8-gap QWR could sta­bly ac­cel­er­ate heavy ion at the ve­loc­i­ties 0.01<v/c<0.05.

• Z.Y. Yao, C. Chang, J.K. Hao, F.S. He, Y.M. Li, L. Lin, K.X. Liu, X.Y. Lu, S.W. Quan, B.C. Zhang, K. Zhao, F. Zhu
  PKU/IHIP, Beijing
• L. Yang
  Peking University, School of Physics, Beijing

Spoke cav­i­ties have been de­vel­oped and have ap­par­ent ad­van­tages for high cur­rent pro­ton ac­cel­er­a­tor based on su­per­con­duc­tiv­i­ty at low and medi­um en­er­gy re­gion. As the re­search and the tech­ni­cal re­serve, Peking Uni­ver­si­ty has start­ed the R&D pro­gram of sin­gle spoke cav­i­ty (SSC). The work is pro­posed to do beam load ex­per­i­ment on the HI-13 Tan­dem at CIAE. The max­i­mum ki­net­ic en­er­gy of pro­ton beam is 26MeV, and the fre­quen­cy of the chop­per for su­per­con­duct­ing is 150MHz. It leads us to the choice of a 450MHz and β=0.2 sin­gle spoke cav­i­ty. In this paper, the RF de­sign, me­chan­i­cal study, fab­ri­ca­tion arts, tol­er­ance anal­y­sis, and room tem­per­a­ture RF test is pre­sent­ed.

• A.T. Wu, S. Jin, R.A. Rimmer
  JLAB, Newport News, Virginia
• X.Y. Lu, K. Zhao
  PKU/IHIP, Beijing

Re­cent ex­per­i­men­tal re­sults have in­di­cat­ed that Buffered Elec­tropol­ish­ing (BEP) is a promis­ing can­di­date for the next gen­er­a­tion of sur­face treat­ment tech­nique for Nb su­per­con­duct­ing radio fre­quen­cy (SRF) cav­i­ties to be used in par­ti­cle ac­cel­er­a­tors. In order to lay the foun­da­tion for using BEP as the next gen­er­a­tion sur­face treat­ment tech­nique for Nb SRF cav­i­ties, some fun­da­men­tal as­pects of BEP treat­ments for Nb have to be in­ves­ti­gat­ed. In this re­port, re­cent progress on BEP study at JLab is shown. Im­prove­ments on the ex­ist­ing ver­ti­cal BEP are made to allow water cool­ing from out­side of a Nb sin­gle cell cav­i­ty in ad­di­tion to cool­ing pro­vid­ed by acid cir­cu­la­tion so that the tem­per­a­ture of the cav­i­ty can be sta­ble dur­ing pro­cess­ing. Some in­ves­ti­ga­tion on the elec­trolyte mix­ture was per­formed to check the aging ef­fect of the elec­trolyte. It is shown that good pol­ish­ing re­sults can still be ob­tained on Nb at a cur­rent den­si­ty of 171 mA/cm when the BEP elec­trolyte was at the sta­tion­ary con­di­tion and was more than 1.5 years old.

* A.T. Wu et al, Proc. of 14th Conference on SRF, Germany, 2009, THPPO064. ** S. Jin et al, the same as 1, THPPO097.
*** F. Eozenou et al, the same as 1 THPPO068.

• A.T. Wu, R.C. Ike, S. Jin, R.A. Rimmer
  JLAB, Newport News, Virginia
• X.Y. Lu, K. Zhao
  PKU/IHIP, Beijing
• L.C. Macintyre
  NSU, Newport News, Virginia

Field emis­sion is still one of the major ob­sta­cles fac­ing Nb su­per­con­duct­ing radio fre­quen­cy (SRF) com­mu­ni­ty for al­low­ing Nb SRF cav­i­ties to reach rou­tine­ly ac­cel­er­at­ing gra­di­ent of 35 MV/m that is re­quired for the in­ter­na­tion­al lin­ear col­lid­er. Nowa­days, the well know low tem­per­a­ture back­ing at 120 oC for 48 hours is a com­mon pro­ce­dure used in the SRF com­mu­ni­ty to im­prove the high field Q slope. How­ev­er, some cav­i­ty pro­duc­tion data have showed that the low tem­per­a­ture bak­ing may in­duce field emis­sion for cav­i­ties treat­ed by EP. On the other hand, an ear­li­er study of field emis­sion on Nb flat sam­ples treat­ed by BCP showed an op­po­site con­clu­sion. In this pre­sen­ta­tion, the pre­lim­i­nary mea­sure­ments of Nb flat sam­ples treat­ed by BEP, EP, and BCP via our unique home-made scan­ning field emis­sion mi­cro­scope be­fore and after the low tem­per­a­ture bak­ing are re­port­ed. Some cor­re­la­tions be­tween sur­face smooth­ness and the num­ber of the ob­served field emit­ters were found. The ob­served ex­per­i­men­tal re­sults can be un­der­stood, at least par­tial­ly, by a sim­ple model that in­volves the change of the thick­ness of the pent-ox­ide layer on Nb sur­faces.

* L.C. MacIntyre, R. Ike, and A.T. Wu, 2005, unpublished