LARP LARP Document 1067-v1

DocDB Home ]  [ Search ] [ Last 20 Days ] [ List Authors ] [ List Topics ] [ List Events ]

Dependence of e-Cloud on the Longitudinal Bunch Profile Studies in the PS & Extension to the HL-LHC

Document #:
LARP-doc-1067-v1
Document type:
Talk
Submitted by:
Chandrashekhara Bhat
Updated by:
Chandrashekhara Bhat
Document Created:
18 Jul 2012, 11:29
Contents Revised:
18 Jul 2012, 11:29
DB Info Revised:
18 Jul 2012, 11:54
Viewable by:
  • Public document
Modifiable by:
Abstract:
Even with the nominal LHC beam parameters the e-cloud related issues are currently prohibiting one to go to 25 ns bunch spacing. During the HL-LHC era the bunch brightness will be 4 x the LHC nominal value. Mitigation of the e-cloud effect in the LHC is highly critical. Some early simulation studies on LHC indicated that the longitudinal profiles of the bunches may have effect on growth of e-cloud and bunch lengthening may be a possible mitigation technique. In this regard we have carried out an experiment in the PS and Bench-marking with e-cloud simulations using ECLOUD and PyECloud. Here we clearly see e-cloud growth dependance on the bunch profile; the bunches in double harmonic rf buckets with harmonic radio of two and V2/V1= 0.5 produce about 2.7 times more electrons than those with V2/V1= -0.5 (bunch lengthening mode). A good agreement is seen between PS e-cloud measurements and the simulations for SEY=1.55-1.6 and R=0.55-0.6. Results are extended to the e-cloud scenarios for the HL-LHC. Our study suggest that the e-cloud dependence on the bunch profile is very small (<20%), unlike in the case of PS. For example bunch profile in bunch lengthening mode with the 400MHz+800MHz rf with V2/V1= -0.5 or water-bag distribution (LARP-doc-1065, version 1) yield similar heat-load, about 20% smaller than LHC nominal bunch shapes or bunch shortening mode with V2/V1= 0.5. Hence, shaping the bunch by adding 800 MHz rf in the LHC may not help with mitigation of e-cloud during the HL-LHC. However, this weak dependence of e-cloud on bunch profile is a good news for the foreseen use of Landau cavity to stabilize high intensity beam in the HL-LHC. (The differences in the e-cloud dependence on the bunch-profile between PS and the LHC may be due to the difference in the mechanisms of e-cloud formation; in LHC all of the primary electrons are produced by synchrotron radiation hitting the beam pipe, while, in the PS they are from the gas ionization.) These studies are in progress.
Files in Document:
  • pdf (ECLOUD12-cbhat-Talk-final.pdf, 2.9 MB)
  • pptx (ECLOUD12-cbhat-Talk-final.pptx, 4.6 MB)
DocDB Home ]  [ Search ] [ Last 20 Days ] [ List Authors ] [ List Topics ] [ List Events ]

DocDB Version 8.7.23, contact LARP Document Database Administrators