SPS Impedance Meeting

Minutes December 12th, 2007

Present: Elias Métral, Giovanni Rumolo, Benoit Salvant, Elena Shaposhnikova. 

Agenda

-  Elena Shaposhnikova  (slides)

"Longitudinal impedance 2007 measurements"

-  Thomas Bohl  (slides)

"Bunch Length 2007 measurements"

-  Rama Calaga  (slides)

"Localization of impedance sources by phase advance vs. intensity"

-  Elias Métral  (slides)

"SPS impedance estimates by Luc Vos in 1986 and 2003"
 

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    Minutes

• Elena Shaposhnikova : Longitudinal impedance measurements

- Results show that the longitudinal emittance in the PS is decreasing with intensity?
- Shaving reduces the slope but increases the scatter.
- Depending on bunch length and longitudinal emittance we can reproduce the results of 2006 or the first meas. in 2007!!!
- Furthermore, it is clearly seen that the same bunch lengths, but with different longitudinal emittances, lead to different results (as expected)...

• Thomas Bohl : Bunch Length measurements

- Thomas described the history of measurement
- From the measurements, it seems that there is less noise with one 80MHz RF cavity than with two cavities.
- The longitudinal emittance mentioned by Thomas and Elena it is the emittance measured with the tomoscope.

Conclusion from Elena and Thomas’ talk:

1) Next year for these measurements, one should ask for the same beam as in 1999 (to be able to compare), i.e. produced in the PSB with H = 2 and vertical shavers => This is one of the beams which need to be prepared for next year!

2) HEADTAIL simulations could be performed to estimate the longitudinal impedance should be performed/started => Benoit could do this as it is the subject of his PHD thesis.

• Rama Calaga : Localization of impedance sources by phase advance vs. intensity

  - Beam kicked at 26 GeV/c, with no octupoles and vertical chromaticity corrected.
  - Analysis of the phase advance between 2 BPMs:
                 1) If there is no impedance between the 2 BPMs, this means that the phase advance does not depend on intensity.
                 2) If there is an impedance between the 2 BPMs, there will be a (negative) slope between the 2 BPMs, and depending on the slope it will be huge or not.
  - The 0-current phase advance (given by the interception of the fitted line with the vertical axis at 0 intensity) should be equal to the MADX model.
  - The phase advance between 2 BPMs in the SPS is slightly less than 90 deg.

  - Next steps:

  - One should not constrain in the analysis that K should be only negative (i.e. assuming only defocusing impedance).
  - Simulate with HEADTAIL what one would expect with the wake field of all (20 in 2006 or 19 in 2007) the kickers.

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