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Multipass beam breakup instability countermeasures in energy recovery linacs

Glukhov, Sergei (2022)
Multipass beam breakup instability countermeasures in energy recovery linacs.
Technische Universität Darmstadt
doi: 10.26083/tuprints-00022915
Ph.D. Thesis, Primary publication, Publisher's Version

Abstract

The multipass regenerative multibunch beam breakup instability is specific to recirculating linacs (linear accelerators) and energy recovery linacs operating in continuous wave mode where particle bunches pass multiple times through the same superconducting RF cavities with extremely high quality factor. Parasitic electromagnetic modes excited in the cavities can affect bunch dynamics in such a way, that on its subsequent passes it excites the modes further and a positive feedback loop is formed. The term "regenerative" means that the effect on a single bunch during its passage through the machine is negligible but the instability develops in time due to persisting fields in the cavities (in opposite to "cumulative" instabilities developing in space when the effect accumulates during the single passage of a bunch through the machine).

Analysis in the time domain (bunch tracking) and the frequency domain (complex current plot technique) may be used to study the instability. Usually only dipole modes are considered, however, in the present work similar approaches are applied to monopole and quadrupole modes and illustrated with simulation results for the S-DALINAC and MESA facilities. An approximated stability analysis technique with better performance for the case of multiple recirculations is proposed. Countermeasures including betatron phase advance adjustment and additional betatron coupling are considered and a universal criterion for assessment of their effectiveness is proposed. A strategy to study the instability experimentally at S-DALINAC is described. A simple model of a damped oscillator with feedback is proposed as a universal example illustrating the phenomenon in general.

Item Type: Ph.D. Thesis
Erschienen: 2022
Creators: Glukhov, Sergei
Type of entry: Primary publication
Title: Multipass beam breakup instability countermeasures in energy recovery linacs
Language: English
Referees: Boine-Frankenheim, Prof. Dr. Oliver ; De Gersem, Prof. Dr. Herbert
Date: 2022
Place of Publication: Darmstadt
Collation: xi, 127 Seiten
Refereed: 17 October 2022
DOI: 10.26083/tuprints-00022915
URL / URN: https://tuprints.ulb.tu-darmstadt.de/22915
Abstract:

The multipass regenerative multibunch beam breakup instability is specific to recirculating linacs (linear accelerators) and energy recovery linacs operating in continuous wave mode where particle bunches pass multiple times through the same superconducting RF cavities with extremely high quality factor. Parasitic electromagnetic modes excited in the cavities can affect bunch dynamics in such a way, that on its subsequent passes it excites the modes further and a positive feedback loop is formed. The term "regenerative" means that the effect on a single bunch during its passage through the machine is negligible but the instability develops in time due to persisting fields in the cavities (in opposite to "cumulative" instabilities developing in space when the effect accumulates during the single passage of a bunch through the machine).

Analysis in the time domain (bunch tracking) and the frequency domain (complex current plot technique) may be used to study the instability. Usually only dipole modes are considered, however, in the present work similar approaches are applied to monopole and quadrupole modes and illustrated with simulation results for the S-DALINAC and MESA facilities. An approximated stability analysis technique with better performance for the case of multiple recirculations is proposed. Countermeasures including betatron phase advance adjustment and additional betatron coupling are considered and a universal criterion for assessment of their effectiveness is proposed. A strategy to study the instability experimentally at S-DALINAC is described. A simple model of a damped oscillator with feedback is proposed as a universal example illustrating the phenomenon in general.

Alternative Abstract:
Alternative abstract Language

Die regenerative Multipass-Beam-Breakup-Strahlinstabilität ist eine spezifische Instabilität von Elektronenstrahlen in rezirkulierenden Linearbeschleunigern im kontinuierlichen Betrieb. Wenn die Teilchen mehrfach durch dieselbe supraleitende Kavität fliegen, werden parasitäre Moden angeregt, die zu einer positiven Rückkopplungsschleife führen können. Der Begriff "regenerativ" bedeutet hier, dass ein einzelner Durchlauf nur einen kleinen Effekt hat. Aber durch die durch mehrere Teilchenpakete akkumulierten Felder in der Kavität entwickelt sich eine Instabilität. Umgekehrt entwickelt sich eine "kumulative" Instabilität durch ein einzelnes Teilchenpaket, welches viele Kicks entlang der Maschine akkumuliert.

Zur Untersuchung der Instabilität können Analysen im Zeitbereich (Bunch-Tracking) und im Frequenzbereich (komplexe Stromplot-Technik) verwendet werden. Normalerweise werden nur Dipolmoden betrachtet. In der vorliegenden Arbeit werden jedoch ähnliche Ansätze auf Monopol- und Quadrupolmoden angewandt und mit Simulationsergebnissen für die Anlagen S-DALINAC und MESA veranschaulicht. Es wird ein Verfahren zur angenäherten Stabilitätsanalyse mit verbesserter Leistung für den Fall mehrerer Rezirkulationen vorgeschlagen. Es werden Gegenmaßnahmen wie die Anpassung des Betatron-Phasenvorschubs und die zusätzliche Betatron-Kopplung in Betracht gezogen und ein universelles Kriterium zur Bewertung ihrer Wirksamkeit vorgeschlagen. Es wird eine Strategie beschrieben, die Instabilität im S-DALINAC experimentell zu untersuchen. Ein einfaches Modell eines gedämpften Oszillators mit Rückkopplung wird als allgemein gehaltenes Beispiel zur Veranschaulichung des Phänomens vorgeschlagen.

German
Uncontrolled Keywords: energy recovery linac, recirculating linac, instability
Status: Publisher's Version
URN: urn:nbn:de:tuda-tuprints-229151
Classification DDC: 500 Science and mathematics > 530 Physics
Divisions: 18 Department of Electrical Engineering and Information Technology
18 Department of Electrical Engineering and Information Technology > Institute for Accelerator Science and Electromagnetic Fields > Accelerator Physics
18 Department of Electrical Engineering and Information Technology > Institute for Accelerator Science and Electromagnetic Fields
Date Deposited: 25 Nov 2022 12:36
Last Modified: 27 Oct 2023 10:35
PPN: 502310944; 503350818
Referees: Boine-Frankenheim, Prof. Dr. Oliver ; De Gersem, Prof. Dr. Herbert
Refereed / Verteidigung / mdl. Prüfung: 17 October 2022
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