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Effects of rf breakdown on the beam in the Compact Linear Collider prototype accelerator structure
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics. (Accelerator Physics)ORCID iD: 0000-0002-6815-2794
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
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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. Vol. 16, no 8, 081004- p.
Keyword [en]
CTF3, CLIC, rf breakdown, kick
National Category
Accelerator Physics and Instrumentation
Research subject
Physics
Identifiers
URN: urn:nbn:se:uu:diva-206207DOI: 10.1103/PhysRevSTAB.16.081004ISI: 000323611000001OAI: oai:DiVA.org:uu-206207DiVA: diva2:644076
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
In thesis
1. Beam Momentum Changes due to Discharges in High-gradient Accelerator Structures
Open this publication in new window or tab >>Beam Momentum Changes due to Discharges in High-gradient Accelerator Structures
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:nbn:se:uu:diva-208567 (URN)978-91-554-8802-4 (ISBN)
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

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