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A Transverse Deflecting Cavity for Longitudinal Beam Measurements on VELA

A Transverse Deflecting Cavity for Longitudinal Beam Measurements on VELA. Louise Cowie. Contents. VELA The transverse deflecting cavity and how it works Design choices Results Conclusion. VELA. TDC. S-band cavity operating at 2.9985 GHz and providing a 5 MV kick

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A Transverse Deflecting Cavity for Longitudinal Beam Measurements on VELA

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  1. A Transverse Deflecting Cavity for Longitudinal Beam Measurements on VELA Louise Cowie

  2. Contents • VELA • The transverse deflecting cavity and how it works • Design choices • Results • Conclusion

  3. VELA

  4. TDC • S-band cavity operating at 2.9985 GHz and providing a 5 MV kick • The cavity gives each electron in the bunch a transverse kick that is proportional to its position • Converts longitudinal to transverse distribution

  5. Transverse force • The force on an electron is • To give an electron travelling in the z direction a transverse kick in the y direction requires either -An electric field in the y direction -A magnetic field in the x direction • Use what is known as a dipole-like mode: TM1np, TE1np

  6. TM110 Magnetic field force

  7. Magnetic field in the x direction

  8. Beam pipe E field Electric field

  9. Electric field in the y direction

  10. Number of cells • Chose a 9 cell 2.9985 GHz cavity as a compromise between HOM separation and shunt impedance. • The cumulative transverse voltage should be around 5 MV • Cell length = one half wavelength = 50 mm • Required gradient = 5 MV / 450mm = 11.11 MV/m

  11. Cell Shape • Chose a well understood multi-cell pillbox shape • As used by Tsinghau University1 and SPARC2

  12. End cells • The end cells were shortened to compensate for the effect of the beampipes. Dipole magnets will also be employed.

  13. Mode separation • Coupler in middle cell does not excite even modes • Coupling holes separate the SOM • Iris radii chosen to maximise mode separation in the pass band • Nearest mode is 6.5 MHz away = 5x cavity bandwidth

  14. Design Timeline Begin re-optimisation September 2012 3-cell prototype ordered March 2012 Begin design September 2011 • Design finished December 2011 • Design finished and 9-cell ordered • December 2012 • Field measurements • July/August 2012

  15. Simulation Results • Frequency of cavity is 2.9985 GHz • R/Q of operating mode is 292.48 Ohms • Q0 = 16046 QE=16140

  16. Field flatness

  17. Conclusions • A 2.9985 GHz cavity giving a 5MV transverse kick was required for VELA • The cavity was designed to meet the requirements and the mechanical designs sent to RI for manufacture

  18. Acknowledgements Thanks to Philippe Goudket and Graeme Burt. References 1. Jiaru Shi et al. Bunch Length Measurement with RF Deflecting Cavity at Tsinhua Thomson-Scattering X-Ray Source. TH5PFP094 Proc. PAC09, Vancouver, Ca. 2. D. Alesini et al., “An RF Deflector Design for 6D Phase Space Characterization of the SPARC Beam”, EPAC’04, Lucerne, July 2004, p. 2616.

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