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Longitudinal intensity effects in the CERN Large Hadron Collider

This PhD thesis provides an improved knowledge of the LHC longitudinal impedance model and a better understanding of the longitudinal intensity effects. These effects can limit the LHC performance and lead to a reduction of the integrated luminosity. The LHC longitudinal impedance was measured with...

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Autor principal: Esteban Muller, Juan
Lenguaje:eng
Publicado: 2016
Materias:
Acceso en línea:http://cds.cern.ch/record/2196930
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author Esteban Muller, Juan
author_facet Esteban Muller, Juan
author_sort Esteban Muller, Juan
collection CERN
description This PhD thesis provides an improved knowledge of the LHC longitudinal impedance model and a better understanding of the longitudinal intensity effects. These effects can limit the LHC performance and lead to a reduction of the integrated luminosity. The LHC longitudinal impedance was measured with beams. Results obtained using traditional techniques are consistent with the expectations based on the impedance model, although the measurement precision was proven insufficient for the low impedance of the LHC. Innovative methods to probe the LHC reactive impedance were successfully used. One of the methods is based on exciting the beam with a sinusoidal rf phase modulation to estimate the synchrotron frequency shift from potential-well distortion. In the second method, the impedance is estimated from the loss of Landau damping threshold, which is also found to be in good agreement with analytical estimations. Beam-based impedance measurements agree well with estimations using the LHC impedance model. Macroparticle simulations of loss of Landau damping reproduce the measurements precisely and are used to determine the current stability limits. The single-bunch stability is analyzed for the HL-LHC, for a bunch intensity almost twice higher than the nominal LHC intensity. The effect of an additional rf system installed for double rf operation provides an increased stability margin in the absence of a wideband longitudinal damper system. The differences between the bunch-shortening and bunch-lengthening operation modes are presented, as well as the effect of an error in the phase synchronization between both rf systems. Several options for the rf parameters are considered, and their advantages and drawbacks under different circumstances are analyzed. A novel diagnostic tool for e-cloud monitoring based on bunch phase measurements has been fully developed. An advanced post-processing was implemented to improve the measurement accuracy up to the required level by reducing systematic and random errors. The tool is available at the CERN Control Room and shows the e-cloud build-up structure along the bunch trains and the total beam power loss due to e-cloud. Phase shift measurements are in good agreement with simulations of the e-cloud buildup and can be used to estimate the heat load in the cryogenic system. The use of this method in operation has been proven to ease the scrubbing run optimization and can eventually be used as an additional input for the cryogenic system.
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spelling cern-21969302019-09-30T06:29:59Zhttp://cds.cern.ch/record/2196930engEsteban Muller, JuanLongitudinal intensity effects in the CERN Large Hadron ColliderAccelerators and Storage RingsThis PhD thesis provides an improved knowledge of the LHC longitudinal impedance model and a better understanding of the longitudinal intensity effects. These effects can limit the LHC performance and lead to a reduction of the integrated luminosity. The LHC longitudinal impedance was measured with beams. Results obtained using traditional techniques are consistent with the expectations based on the impedance model, although the measurement precision was proven insufficient for the low impedance of the LHC. Innovative methods to probe the LHC reactive impedance were successfully used. One of the methods is based on exciting the beam with a sinusoidal rf phase modulation to estimate the synchrotron frequency shift from potential-well distortion. In the second method, the impedance is estimated from the loss of Landau damping threshold, which is also found to be in good agreement with analytical estimations. Beam-based impedance measurements agree well with estimations using the LHC impedance model. Macroparticle simulations of loss of Landau damping reproduce the measurements precisely and are used to determine the current stability limits. The single-bunch stability is analyzed for the HL-LHC, for a bunch intensity almost twice higher than the nominal LHC intensity. The effect of an additional rf system installed for double rf operation provides an increased stability margin in the absence of a wideband longitudinal damper system. The differences between the bunch-shortening and bunch-lengthening operation modes are presented, as well as the effect of an error in the phase synchronization between both rf systems. Several options for the rf parameters are considered, and their advantages and drawbacks under different circumstances are analyzed. A novel diagnostic tool for e-cloud monitoring based on bunch phase measurements has been fully developed. An advanced post-processing was implemented to improve the measurement accuracy up to the required level by reducing systematic and random errors. The tool is available at the CERN Control Room and shows the e-cloud build-up structure along the bunch trains and the total beam power loss due to e-cloud. Phase shift measurements are in good agreement with simulations of the e-cloud buildup and can be used to estimate the heat load in the cryogenic system. The use of this method in operation has been proven to ease the scrubbing run optimization and can eventually be used as an additional input for the cryogenic system.CERN-THESIS-2016-066oai:cds.cern.ch:21969302016-07-06T09:11:34Z
spellingShingle Accelerators and Storage Rings
Esteban Muller, Juan
Longitudinal intensity effects in the CERN Large Hadron Collider
title Longitudinal intensity effects in the CERN Large Hadron Collider
title_full Longitudinal intensity effects in the CERN Large Hadron Collider
title_fullStr Longitudinal intensity effects in the CERN Large Hadron Collider
title_full_unstemmed Longitudinal intensity effects in the CERN Large Hadron Collider
title_short Longitudinal intensity effects in the CERN Large Hadron Collider
title_sort longitudinal intensity effects in the cern large hadron collider
topic Accelerators and Storage Rings
url http://cds.cern.ch/record/2196930
work_keys_str_mv AT estebanmullerjuan longitudinalintensityeffectsinthecernlargehadroncollider