Cargando…

Transverse Emittance Measurement and Preservation at the LHC

The Large Hadron Collider (LHC) at CERN is a high energy storage ring that provides proton and heavy ion collisions to study fundamental particle physics. The luminosity production is closely linked to emittance preservation in the accelerator. The transverse emittance is the phase space density of...

Descripción completa

Detalles Bibliográficos
Autor principal: Kuhn, Maria
Lenguaje:eng
Publicado: 2016
Materias:
Acceso en línea:http://cds.cern.ch/record/2229712
_version_ 1780952507521957888
author Kuhn, Maria
author_facet Kuhn, Maria
author_sort Kuhn, Maria
collection CERN
description The Large Hadron Collider (LHC) at CERN is a high energy storage ring that provides proton and heavy ion collisions to study fundamental particle physics. The luminosity production is closely linked to emittance preservation in the accelerator. The transverse emittance is the phase space density of the beam and should be conserved when the particle beam is transformed through the accelerator. Perturbing effects, however, can lead to emittance increase and hence luminosity degradation. Measuring the emittance growth is a complex task with high intensity beams and changing energies. The machine optics and the transverse beam size have to be measured as accurately as possible. Beta function measurements with k-modulation will be discussed. With this method the quadrupole focussing strength is varied and the resulting tune change is traced to determine the beta function at the quadrupole. A new k-modulation measurement tool was developed for the LHC. The fully automatic and online measurement system takes constraints of various systems such as tune measurement precision and powering limitations of the LHC superconducting circuits into account. With sinusoidal k-modulation record low beta function measurement uncertainties in the LHC have been reached. 2015 LHC beta function and β*, which is the beta function at the collision point, measurements with k-modulation will be presented. Wire scanners and synchrotron light monitors are presently used in the LHC to measure the transverse beam size. Accuracy and limitations of the LHC transverse profile monitors will be discussed. During the 2012 LHC proton run it was found that wire scanner photomultiplier saturation added significant uncertainty on all measurements. A large discrepancy between emittances from wire scanners and luminosity was discovered but not solved. During Long Shutdown 1 the wire scanner system was upgraded with new photomultipliers. A thorough study of LHC wire scanner measurement precision in 2015 will be presented. During LHC Run 1 significant transverse emittance growth throughout the LHC cycle was observed. About 30 % of the potential luminosity performance was lost through the different phases of the LHC cycle. At the LHC design stage the total allowed emittance increase through the cycle was set to 7 %. Measurements indi- cated that most of the blow-up occurred during the injection plateau and the ramp. Intra-beam scattering was one of the main drivers for emittance growth. In April 2015 the LHC re-started with a collision energy of 6.5 TeV per beam. This thesis presents the first transverse emittance preservation studies in LHC Run 2 with 25 ns beams. A breakdown of the growth throughout the various phases in the LHC cycle is given for low intensity beams measured with wire scanners. Also presented is data collected from synchrotron light monitors and the LHC experiments. Finally, the emittance growth results will be compared to intra-beam scattering simulations. A theory on emittance growth due to noise from the LHC transverse damper and other external sources will be discussed. The results of the investiga- tions are summarized and an outlook in terms of emittance blow-up for future LHC upgrade scenarios with low emittance beams will be given.
id cern-2229712
institution Organización Europea para la Investigación Nuclear
language eng
publishDate 2016
record_format invenio
spelling cern-22297122019-09-30T06:29:59Zhttp://cds.cern.ch/record/2229712engKuhn, MariaTransverse Emittance Measurement and Preservation at the LHCAccelerators and Storage RingsThe Large Hadron Collider (LHC) at CERN is a high energy storage ring that provides proton and heavy ion collisions to study fundamental particle physics. The luminosity production is closely linked to emittance preservation in the accelerator. The transverse emittance is the phase space density of the beam and should be conserved when the particle beam is transformed through the accelerator. Perturbing effects, however, can lead to emittance increase and hence luminosity degradation. Measuring the emittance growth is a complex task with high intensity beams and changing energies. The machine optics and the transverse beam size have to be measured as accurately as possible. Beta function measurements with k-modulation will be discussed. With this method the quadrupole focussing strength is varied and the resulting tune change is traced to determine the beta function at the quadrupole. A new k-modulation measurement tool was developed for the LHC. The fully automatic and online measurement system takes constraints of various systems such as tune measurement precision and powering limitations of the LHC superconducting circuits into account. With sinusoidal k-modulation record low beta function measurement uncertainties in the LHC have been reached. 2015 LHC beta function and β*, which is the beta function at the collision point, measurements with k-modulation will be presented. Wire scanners and synchrotron light monitors are presently used in the LHC to measure the transverse beam size. Accuracy and limitations of the LHC transverse profile monitors will be discussed. During the 2012 LHC proton run it was found that wire scanner photomultiplier saturation added significant uncertainty on all measurements. A large discrepancy between emittances from wire scanners and luminosity was discovered but not solved. During Long Shutdown 1 the wire scanner system was upgraded with new photomultipliers. A thorough study of LHC wire scanner measurement precision in 2015 will be presented. During LHC Run 1 significant transverse emittance growth throughout the LHC cycle was observed. About 30 % of the potential luminosity performance was lost through the different phases of the LHC cycle. At the LHC design stage the total allowed emittance increase through the cycle was set to 7 %. Measurements indi- cated that most of the blow-up occurred during the injection plateau and the ramp. Intra-beam scattering was one of the main drivers for emittance growth. In April 2015 the LHC re-started with a collision energy of 6.5 TeV per beam. This thesis presents the first transverse emittance preservation studies in LHC Run 2 with 25 ns beams. A breakdown of the growth throughout the various phases in the LHC cycle is given for low intensity beams measured with wire scanners. Also presented is data collected from synchrotron light monitors and the LHC experiments. Finally, the emittance growth results will be compared to intra-beam scattering simulations. A theory on emittance growth due to noise from the LHC transverse damper and other external sources will be discussed. The results of the investiga- tions are summarized and an outlook in terms of emittance blow-up for future LHC upgrade scenarios with low emittance beams will be given.CERN-THESIS-2016-149oai:cds.cern.ch:22297122016-11-03T19:52:57Z
spellingShingle Accelerators and Storage Rings
Kuhn, Maria
Transverse Emittance Measurement and Preservation at the LHC
title Transverse Emittance Measurement and Preservation at the LHC
title_full Transverse Emittance Measurement and Preservation at the LHC
title_fullStr Transverse Emittance Measurement and Preservation at the LHC
title_full_unstemmed Transverse Emittance Measurement and Preservation at the LHC
title_short Transverse Emittance Measurement and Preservation at the LHC
title_sort transverse emittance measurement and preservation at the lhc
topic Accelerators and Storage Rings
url http://cds.cern.ch/record/2229712
work_keys_str_mv AT kuhnmaria transverseemittancemeasurementandpreservationatthelhc