• 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