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Beam Momentum Changes due to Discharges in High-gradient Accelerator Structures
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.ORCID iD: 0000-0002-6815-2794
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The key questions left unanswered by the Standard Model, and the recent discovery of a Standard Model-like Higgs boson, demand an extension of the research on particle physics to the TeV energy scale. The Compact Linear Collider, CLIC, is a candidate project to achieve such goal. It is a linear lepton collider based on a novel two-beam acceleration scheme capable of high-gradient acceleration in X-band accelerator structures. The high electric fields required, however, entail the occurrence of vacuum discharges, or rf breakdowns, a phenomenon whose microscopic dynamics is not yet completely understood, and whose impact on the beam can lead to a severe degradation of the collider luminosity.

The understanding of the physics of rf breakdowns has therefore become a significant issue in the design of a reliable accelerator based on CLIC technology. That is addressed experimentally through the study of accelerator structures performance during high-power operations. We report on such a study carried out on a CLIC prototype structure assembled in a resonant ring at SLAC. We characterise the experimental set-up through a complex least square analysis, and we show how breakdowns can be localised in the structure on the basis of rf measurements.

The same methodology lays the ground for the study of the impact of rf breakdowns on the beam. We addressed that issue at the Two-beam Test Stand, an experimental area built within the CLIC Test Facility CTF3 at CERN, where we tested a CLIC prototype accelerator structure in the presence of an electron beam. There, we found that rf breakdowns can affect both the longitudinal and the transverse beam momentum, causing a reduction of accelerating gradient and transverse kicks to the beam trajectory. In view of the CLIC design, we finally discuss what is the impact of such effects on the collider luminosity, which can be drastically reduced.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 85 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1096
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:uu:diva-208567ISBN: 978-91-554-8802-4 (print)OAI: oai:DiVA.org:uu-208567DiVA: diva2:660614
Public defence
2013-12-12, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Funder
Knut and Alice Wallenberg Foundation, 2004-0122Knut and Alice Wallenberg Foundation, 2009-0244Swedish Research Council, 2005-4474Swedish Research Council, 2010-6027Swedish Research Council, 2011-6305Swedish Research Council, 2009-6234EU, FP7, Seventh Framework Programme, 227579
Available from: 2013-11-21 Created: 2013-10-03 Last updated: 2014-01-23
List of papers
1. Effects of rf breakdown on the beam in the Compact Linear Collider prototype accelerator structure
Open this publication in new window or tab >>Effects of rf breakdown on the beam in the Compact Linear Collider prototype accelerator structure
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2013 (English)In: Physical Review Special Topics. Accelerators and Beams, ISSN 1098-4402, E-ISSN 1098-4402, Vol. 16, no 8, 081004- p.Article in journal (Refereed) Published
Abstract [en]

Understanding the effects of rf breakdown in high-gradient accelerator structures on the acceleratedbeam is an extremely relevant aspect in the development of the Compact Linear Collider (CLIC) andis one of the main issues addressed at the Two-beam Test Stand at the CLIC Test Facility 3 at CERN.During a rf breakdown high currents are generated causing parasitic magnetic fields that interact withthe accelerated beam affecting its orbit. The beam energy is also affected because the power is partlyreflected and partly absorbed thus reducing the available energy to accelerate the beam. We discusshere measurements of such effects observed on an electron beam accelerated in a CLIC prototypestructure. Measurements of the trajectory of bunch trains on a nanosecond time scale showed fastchanges in correspondence of breakdown that we compare with measurements of the relative beamspots on a scintillating screen. We identify different breakdown scenarios for which we offer anexplanation based also on measurements of the power at the input and output ports of the acceleratorstructure. Finally we present the distribution of the magnitude of the observed changes in the beamposition and we discuss its correlation with rf power and breakdown location in the acceleratorstructure.

Place, publisher, year, edition, pages
APS, 2013
Keyword
CTF3, CLIC, rf breakdown, kick
National Category
Accelerator Physics and Instrumentation
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-206207 (URN)10.1103/PhysRevSTAB.16.081004 (DOI)000323611000001 ()
Funder
EU, FP7, Seventh Framework Programme, 227579Swedish Research Council, 2005-4474, 2010-6027, 2011-6305Knut and Alice Wallenberg Foundation
Available from: 2013-08-29 Created: 2013-08-29 Last updated: 2017-12-06Bibliographically approved
2. High-gradient test of a X-band accelerator structure assembled in a klystron-driven resonant ring
Open this publication in new window or tab >>High-gradient test of a X-band accelerator structure assembled in a klystron-driven resonant ring
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(English)In: Physical Review Special Topics. Accelerators and Beams, ISSN 1098-4402, E-ISSN 1098-4402Article in journal (Refereed) Submitted
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-208565 (URN)
Available from: 2013-10-03 Created: 2013-10-03 Last updated: 2017-12-06Bibliographically approved
3. The CTF3 Two-beam Test Stand
Open this publication in new window or tab >>The CTF3 Two-beam Test Stand
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2013 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 729, 546-553 p.Article in journal (Refereed) Published
Abstract [en]

The Two-beam Test Stand (TBTS) has been constructed and operated at the CLIC test facility CTF3 at CERN. The TBTS comprises two parallel and independent electron beam lines and has been designed to demonstrate the feasibility of a two-beam high gradient acceleration concept as proposed for the Compact Linear Collider (CLIC). In the CLIC scheme, the RF power is extracted from a high current drive beam using RF power extraction structures while the main beam is accelerated using this RF power which is fed into high gradient high frequency normal conducting accelerating structures. The Two-beam Test Stand is a unique facility to demonstrate the feasibility of the CLIC two-beam high gradient acceleration concept and to test the individual CLIC components and complete two-beam CLIC modules. The TBTS is particularly well suited to investigate the effects on the beam of RF breakdown in the high gradient accelerating structures. We report on the design, construction and commissioning of the Two-beam Test Stand.

Keyword
Two-beam acceleration, RF breakdown, CLIC, CTF3
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-208218 (URN)10.1016/j.nima.2013.07.055 (DOI)000325753500076 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2013-09-25 Created: 2013-09-25 Last updated: 2017-12-06Bibliographically approved
4. Two Beam Test Stand Experiments in the CTF3 Facility
Open this publication in new window or tab >>Two Beam Test Stand Experiments in the CTF3 Facility
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2011 (English)Conference paper, Published paper (Refereed)
Abstract [en]

The CLEX building in the CTF3 facility is the placewhere essential experiments are performed to validate theTwo-Beam Acceleration scheme upon which the CLICproject relies. The Drive Beam enters the CLEX hall afterbeing recombined in the Delay loop and the CombinerRing in intense beam trains of 24 A – 120 MeV lasting140 ns and bunched at 12 GHz, although other beamparameters are also accessible. This beam is thendecelerated in dedicated structures installed in the TestBeam Line (TBL) and in the Two-Beam Test Stand(TBTS) aimed at delivering bursts of 12 GHz RF power.In the TBTS this power is used to generate a highaccelerating gradient of 100 MV/m in specially designedaccelerating structures. To assess the performances ofthese structures a probe beam is used, produced by asecond Linac. We report here various experimentsconducted in the TBTS making use of the versatility ofthe probe beam and of dedicated diagnostics.

National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-170216 (URN)
Conference
IPAC2011, San Sebastián, Spain
Available from: 2012-03-09 Created: 2012-03-09 Last updated: 2014-01-23
5. Commissioning of inductive BPMs in the TBTS probe beam line
Open this publication in new window or tab >>Commissioning of inductive BPMs in the TBTS probe beam line
2013 (English)Report (Other academic)
National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-210018 (URN)
Available from: 2013-10-29 Created: 2013-10-29 Last updated: 2014-01-23

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