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Beam Diagnostics and Dynamics in Nonlinear Fields
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Particle accelerators are indispensable tools for probing matter at the smallest scales and the improvements of such tools depend on the progress and understanding of accelerator physics. The Compact Linear Collider (CLIC) is a proposed, linear electron–­positron collider on the TeV-scale, based at CERN. In such a large accelerator complex, diagnostics and alignment of the beam are crucial in order to maintain beam quality and luminosity. In this thesis we have utilized the nonlinear fields from the octupole component of the radio-frequency fields in the CLIC accelerating structures for beam-based diagnostics. We have investigated methods where the nonlinear position shifts of the beam are used to measure the strength of the octupole component and can also be used for alignment. Furthermore, from the changes in transverse beam profile, due to the nonlinear octupole field, we determine the full transverse beam matrix, which characterizes the transverse distribution of the beam.

In circular accelerators, nonlinear fields result in nonlinear beam dynamics, which often becomes the limiting factor for long-term stability. In theoretical studies and simulations we investigate optimum configurations for octupole magnets that compensate amplitude-dependent tune-shifts but avoid driving fourth-order resonances and setups of sextupole magnets to control individual resonance driving terms in an optimal way.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. , p. 87
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1583
Keywords [en]
Beam diagnostics, Nonlinear beam dynamics, Accelerator physics
National Category
Accelerator Physics and Instrumentation
Identifiers
URN: urn:nbn:se:uu:diva-330975ISBN: 978-91-513-0121-1 (print)OAI: oai:DiVA.org:uu-330975DiVA, id: diva2:1150718
Public defence
2017-12-08, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-11-15 Created: 2017-10-19 Last updated: 2018-03-07
List of papers
1. Measuring the full transverse beam matrix using a single octupole
Open this publication in new window or tab >>Measuring the full transverse beam matrix using a single octupole
2015 (English)In: Physical Review Special Topics. Accelerators and Beams, ISSN 1098-4402, E-ISSN 1098-4402, Vol. 18, no 7, article id 072801Article in journal (Refereed) Published
Abstract [en]

We propose a method to fully determine the transverse beam matrix using a simple setup consisting of two steering magnets, an octupole field and a screen. This works in principle for any multipole field, i.e., sextupole, octupole magnet or a radio frequency structure with a multipole field. We have experimentally verified the method at the Compact Linear Collider Test Facility 3 at CERN using a Compact Linear Collider accelerating structure, which has an octupole component of the radio frequency fields. By observing the position shifts of the beam centroid together with changes in transverse beam size on a screen, we determined the full transverse beam matrix, with all correlations.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-259088 (URN)10.1103/PhysRevSTAB.18.072801 (DOI)000357647600001 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council, 2011-6305, 2014-6360
Available from: 2015-07-29 Created: 2015-07-27 Last updated: 2017-12-04Bibliographically approved
2. Aligning linac accelerating structures using a copropagating octupolar mode
Open this publication in new window or tab >>Aligning linac accelerating structures using a copropagating octupolar mode
2017 (English)In: Physical Review Accelerators and Beams, ISSN 2469-9888, Vol. 20, article id 102801Article in journal (Refereed) Published
Abstract [en]

We propose a novel method to align accelerating structures such as those used in the Compact Linear Collider (CLIC) by exploiting a mode that copropagates with the normal accelerating mode. This mode has an octupolar dependence in the transverse direction and is caused by radial waveguides intended to damp higher-order modes. The nonlinear dependence of the octupolar mode makes it possible to determine the center of the structure from the nonlinear dependence of the transverse kick, observed on a downstream beam position monitor, while changing the transverse position of the beam with respect to the accelerating structures. We discuss the method, its tolerances and disentangling the individual misalignments of two adjacent accelerating structures that are powered from a single source.

Place, publisher, year, edition, pages
College Park, MD: American Physical Society, 2017
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-331616 (URN)10.1103/PhysRevAccelBeams.20.102801 (DOI)000413054500001 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council, 2011-6305Swedish Research Council, 2014-6360
Available from: 2017-10-16 Created: 2017-10-16 Last updated: 2018-01-29Bibliographically approved
3. Beam-based alignment studies at CTF3 using the octupole component of CLIC accelerating structures
Open this publication in new window or tab >>Beam-based alignment studies at CTF3 using the octupole component of CLIC accelerating structures
Show others...
2017 (English)In: in Proceedings of the 8th International Particle Accelerator Conference (IPAC 2017), Copenhagen, Denmark, May, 2017., 2017Conference paper, Published paper (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-329988 (URN)978-3-95450-182-3 (ISBN)
Conference
IPAC 2017
Available from: 2017-09-25 Created: 2017-09-25 Last updated: 2017-10-19
4. Compensating amplitude-dependent tune-shift without driving fourth-order resonances
Open this publication in new window or tab >>Compensating amplitude-dependent tune-shift without driving fourth-order resonances
2017 (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. 869, p. 1-9Article in journal (Refereed) Published
Abstract [en]

If octupoles are used in a ring to correct the amplitude-dependent tune-shift one normally tries to avoid that the octupoles drive additional resonances. Here we consider the optimum placement of octupoles that only affects the amplitude-dependent tune-shift, but does not drive fourth-order resonances. The simplest way turns out to place three equally powered octupoles with 60° phase advance between adjacent magnets. Using two such octupole triplets separated by a suitable phase advance cancels all fourth-order resonance driving terms and forms a double triplet we call a six-pack. Using three six-packs at places with different ratios of the beta functions allows to independently control all amplitude-dependent tune-shift terms without exciting additional fourth-order resonances in first order of the octupole excitation.

Keywords
Beam dynamics, Nonlinear beam dynamics
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-329979 (URN)10.1016/j.nima.2017.06.047 (DOI)000409530200001 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research Council, 2011-6305, 2014-6360
Available from: 2017-09-25 Created: 2017-09-25 Last updated: 2017-12-05Bibliographically approved
5. Optimum resonance control knobs for sextupoles
Open this publication in new window or tab >>Optimum resonance control knobs for sextupoles
2018 (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. 894, p. 111-118Article in journal (Refereed) Published
Abstract [en]

We discuss the placement of extra sextupoles in a magnet lattice that allows to correct third-order geometric resonances, driven by the chromaticity-compensating sextupoles, in a way that requires the least excitation of the correction sextupoles. We consider a simplified case, without momentum-dependent effects or other imperfections, where suitably chosen phase advances between the correction sextupoles leads to orthogonal knobs with equal treatment of the different resonance driving terms.

National Category
Accelerator Physics and Instrumentation
Identifiers
urn:nbn:se:uu:diva-330972 (URN)10.1016/j.nima.2018.03.041 (DOI)000430704600014 ()
Funder
Swedish Research Council, 2011-6305Swedish Research Council, 2014-6360Knut and Alice Wallenberg Foundation
Available from: 2017-10-09 Created: 2017-10-09 Last updated: 2018-08-03Bibliographically approved
6. Surface Characterization and Field Emission Measurements of Copper Samples inside a Scanning Electron Microscope
Open this publication in new window or tab >>Surface Characterization and Field Emission Measurements of Copper Samples inside a Scanning Electron Microscope
2016 (English)Conference paper, Published paper (Other academic)
Abstract [en]

Vacuum breakdown in normal-conducting accelerating structures is a limiting factor for high gradient acceleration.Many aspects of the physics governing the breakdown process and its onset are yet to be fully understood. At Uppsala University we address these questions with an in-situ experi-mental setup mounted in an environmental scanning electron microscope. It consists of a piezo motor driven tungsten needle and a sample surface mounted on a piezo stage, allowing for nano-meter 3D-position control. One of the piezomotors controls the needle-sample gap while the two otherscan across the surface. A DC-voltage up to 1 kV is  applied across the gap and field emission currents from a coppersurface are measured with an electrometer. Here we presentthe setup and some initial results.

National Category
Accelerator Physics and Instrumentation Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-298811 (URN)
Conference
the 7th International Particle Accelerator Conference IPAC16 in Busan, South Korea, May 2016
Available from: 2016-07-08 Created: 2016-07-08 Last updated: 2017-10-19Bibliographically approved

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