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RF MD: Long bunches

RF MD: Long bunches. J.F. Esteban Müller , C . Bhat, P. Baudrenghien, T . Bohl, T. Mastoridis, G . Papotti , E. Shaposhnikova , H. Timko , U. Wehrle. Motivation. Longer bunches: Help to r educe heating in MKI, beam screens and collimators Less e-cloud effect

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RF MD: Long bunches

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  1. RF MD: Long bunches J.F. Esteban Müller, C. Bhat, P. Baudrenghien, T. Bohl, T. Mastoridis, G. Papotti, E. Shaposhnikova, H. Timko, U. Wehrle LSWG

  2. Motivation • Longer bunches: • Help to reduce heating in MKI, beam screens and collimators • Less e-cloud effect • For the same voltage  Larger emittance: • Better stability • Lower IBS growth rate • But potentially more particle losses (degraded beam lifetime) • Goal of the MD: measure lifetime vs. bunch length LSWG

  3. Conditions • 8 bunches/ring in buckets spaced by 1/9th turn • Nominal beam and machine conditions: • Longitudinal emittances at injection (~0.5eVs) • Nominal intensity per bunch with large spread (1.15 ± 0.15x1011p) • Nominal voltage program • At 3.5 TeV, blow-up modulated along the ring to achieve spread in bunch length • Voltage reduced at the end of the study to further increase bunch length LSWG

  4. Modulated longitudinal blow-up • Ramp: blow-up target to 1ns (1.25ns operation) • Flat top: phase noise with amplitude modulated at frev • Lengths between 1.15-1.50ns B1 and 1.25-1.65ns B2 Firmware designed by J. Molendijk LSWG

  5. Losses after blow-up • For each voltage settings we observe a statistical increase of losses with bunch length LSWG

  6. Conclusions • Longer bunches lose more particles, as expected. • Degradation of lifetime during one hour observation: from ~0.5%/h @ 1.2 ns to ~1.0 %/h @ 1.4 ns • Beam-beam effects could increase loss rate • Next step could be a physics fill with 1.3 ns at end ramp (instead of present 1.2 ns) LSWG

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