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Ecloud MD 10nov2010

Ecloud MD 10nov2010. SPSU Study Group 17 Feb 2011. Context. 50 ns bunch spacing Intensity around 8e10 p/b (from FBCT) Injection of 3 batches Strong decrease of vertical chromaticity at flat top led to vertical instability Other measurements in parallel Damper was most likely on.

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Ecloud MD 10nov2010

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  1. Ecloud MD 10nov2010 SPSU Study Group 17 Feb 2011

  2. Context • 50 ns bunch spacing • Intensity around 8e10 p/b (from FBCT) • Injection of 3 batches • Strong decrease of vertical chromaticity at flat top led to vertical instability • Other measurements in parallel • Damper was most likely on

  3. LHC BPM data

  4. Observed vertical instability when vertical chromaticity is low Low chromaticity at flat top High chromaticity at flat top stable Unstable (single or coupled bunch?)

  5. Low chromaticity at flat top

  6. Low chromaticity at flat top

  7. High chromaticity at flat top

  8. BPW data

  9. Low chromaticity (QPV=0.18) • - Instability at the end of the second batch • Small shift to the left is also seen in sum signal  no higher order mode visible •  Coupled bunch instability or chromaticity<0?

  10. High chromaticity (QPV=0.68)  Much more stable

  11. lower chromaticity (QPV=0.15)  Very unstable motion (again mode 0), but losses not consistent with negative chromaticity… However, damper was on

  12. Conclusions • Vertical coherent instability observed with low chromaticity (negative?  then damped by damper but not all bunches are treated equally) • Mode 0 and coherent motion along the bunch point to a coupled bunch instability.

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