Author: Cao, S.S.
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WEPAF027 Low Q Cavity BPM Study for the Beam Position Measurement of Nanosecond Spaced Electron Bunches 1881
  • L. Yang, X. He, L.W. Zhang
    CAEP/IFP, Mainyang, Sichuan, People's Republic of China
  • S.S. Cao, Y.B. Leng, L.Y. Yu, R.X. Yuan
    SINAP, Shanghai, People's Republic of China
  Funding: National natural science foundation of China, 11705184
Low Q cavity BPM is a key to distinguish closely spaced electron bunches allowing precise beam handling for XFEL facilities operating in a multi-bunch mode at high repetition rate up to hundreds MHz. The inter-bunch signal pollution issue becomes significant when bunch separation is down to nanosecond and causes the position detection to be increasingly overestimated. Solely relying on extreme low Q to achieve sufficient decay within bunch interval leads to appreciable interference from non-signal modes due to strong overcoupling of antenna design is required. The error imposed on measured position raises a challenge to meet the goal of high resolution. Alternatively, a concept is proposed to remove the dominant part of signal pollution at the moment of sampling by intentionally shifting the phase of the last bunch signal 90degree respect to that of current bunch signal, where signal sampling is normally taken for nanosecond spaced bunches. This quadrature phase shift is defined by properly choosing the operational frequency of dipole mode regarding to the bunch frequency. A low Q cavity BPM prototype to identify technical challenges and verify this concept is under development in the R&D plan for future XFEL with high repetition rate
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THPML061 X-Band Low Q Cavity Beam Position Monitor Study 4777
SUSPF093   use link to see paper's listing under its alternate paper code  
  • S.S. Cao
    SINAP, Shanghai, People's Republic of China
  • Y.B. Leng, R.X. Yuan
    SSRF, Shanghai, People's Republic of China
  The high repetition-rate and high peak brilliance of X-ray free-electron laser (XFEL) allow studying many scientific experiments that have not been feasible. To realize such high performance, a sub-micron beam transverse position measurement is required. The cavity-type beam position monitor (CBPM), as a non-destructive diagnostics tool with high potential in resolution performance, has been applied in different free electron laser facilities (FELs). In this research, an X-band high bandwidth CBPM has been studied and used for pre-research on bunch-by-bunch diagnostic for the pulsed FEL with high repetition-rate. Its bandwidth reaches 300 MHz. Design considerations and simulation results of the CBPM have been discussed and presented in this paper.  
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