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Bunch Profile Dependence of E-Cloud: An Experimental Study in the PS & Application to the High Luminosity LHC

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Chandrashekhara Bhat
Updated by:
Chandrashekhara Bhat
Document Created:
02 Jul 2013, 11:06
Contents Revised:
09 Jul 2013, 14:18
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09 Jul 2013, 14:18
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09 Jul 2013, 14:07
02 Jul 2013, 11:31
02 Jul 2013, 11:06
Increasing the bunch intensity in the LHC for the luminosity upgrade will be severely limited by the e-cloud build up. ECLOUD simulations suggested that longitudinally flat bunches can reduce the e-cloud related heat load on the LHC cryo-system. The objective of the current MD is to characterize the e-cloud effect on the shape of the bunch profile. The PS plays a unique role in the CERN complex that prepares beam as per the LHC specifications and can give varieties of shapes to the bunch profile just before ejection. In the past, e-cloud is observed and measured in the PS on the LHC25 cycle (intensity ~1.1E11 ppb) at 26 GeV from the last splitting till the beam ejection [1]. Here, we have studied the e-cloud effects on the similar PS cycle but by changing the shape of the bunch profile using double harmonic rf system comprising of 40 MHz (h=84) and 80 MHz (h=168) rf cavities. The experiments have been carried out with bunch intensities ~25% larger than the past measurements [1] and on nominal bunches, bunch lengthening mode (BLM) and bunch shortening mode (BSM). Attempt is made to compare the measured data with the simulations. Finally, we make an extrapolation to the HL-LHC cases.

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