The bilinear-exponential closed-orbit model and its application to storage ring beam diagnostics
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Date
2016
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Abstract
Im periodischen Fokussiersystem eines Speicherrings wird der Teilchenstrahl auf einen geschlossenen Orbit, d.h. eine sich wiederholende Teilchenbahn durch den Beschleuniger, abgebildet. Störungen dieses geschlossenen Orbits werden durch fehlerhafte Beschleunigerelemente erzeugt und durch spezielle Magnetstrukturen (Korrektoren) kompensiert. Die zur Kompensation erforderliche Diagnose über Strahlpositionsmonitore (BPMs) sowie die ebenfalls notwendige Charakterisierung der Korrektoren über Messung der sog. Responsematrix wird routinemäßig an vielen Speicherringen weltweit durchgeführt. Weiterhin ist die Bewegung der Einzelteilchen um den geschlossenen Orbit (Strahloptik) aus Stabilitätsgründen interessant, konnte jedoch bisher nur mittels zusätzlicher Spezialhardware beobachtet oder näherungsweise durch Simulation mithilfe eines vollständigen magnetischen Modells des Beschleunigers abgeschätzt werden.
Es ist bekannt, dass in Responsematrizen ebenfalls aufschlussreiche Informationen über die Einzelteilchenbewegung um die Sollbahn (Strahloptik), wenn auch in verschlüsselter Form, enthalten sind. Da Responsematrizen routinemäßig an vielen Speicherringen aufgenommen werden und keine zusätzliche Hardware erfordern, ist ihre "Entschlüsselung" von besonderem Interesse.
In der vorliegenden Arbeit wird ein Algorithmus mit dem Namen COBEA (Closed-Orbit Bilinear-Exponential Analysis) entwickelt, mit dessen Hilfe Responsematrizen in strahloptische Informationen zerlegt werden können. Grundlage dafür ist eine reduzierte und zugleich verallgemeinerte Darstellung der Störungen des geschlossenen Orbits (Bilinear-Exponentielles Modell) in Abhängigkeit von Strahlparametern an Monitor- und Korrektorpositionen. Abschliessend wird COBEA an drei Speicherringen (DELTA, MLS, BESSY II) mit existierenden Methoden, welche alle entweder zusätzliche Hardware oder zusätzliche Annahmen erfordern, verglichen und erfolgreich validiert. COBEA kann somit an vielen Speicherringen weltweit eingesetzt werden.
In periodic focusing systems of accelerators, the particle beam is mapped onto its own closed trajectory (respectively closed orbit). Perturbations of this closed orbit are induced by imperfect accelerator parts and can be compensated by special magnetic devices (correctors). The beam diagnostics using beam position monitors (BPMs), as well as the characterization of corrector magnets by measurement of a so-called response matrix, which are both needed for orbit correction, are routinely performed at many storage rings around the world. Furthermore, the single-particle motion (beam optics) around the closed orbit is of interest due to its implication on beam stability and performance, but could hitherto only be observed by use of additional special hardware or, in approximation, by simulations using the complete magnetic setup of the respective storage ring. It is known that response matrices hold significant information about beam optics, although in an encrypted form. As response matrices are routinely measured at many storage rings without additional hardware, their decomposition is of particular interest. In the present work, an algorithm called Closed-Orbit Bilinear-Exponential Analysis (COBEA) is being developed, with which it is possible to decompose response matrices into beam-optical information with a minimal set of assumptions. The analysis is based on a reduced and simulataneously generalized description of closed-orbit perturbations in dependence of beam parameters at monitor and corrector positions. In closing, COBEA is compared against existing measurement methods, which either need more hardware or more assumptions, and is succesfully validated against them. COBEA can therefore be used at many storage rings around the world.
In periodic focusing systems of accelerators, the particle beam is mapped onto its own closed trajectory (respectively closed orbit). Perturbations of this closed orbit are induced by imperfect accelerator parts and can be compensated by special magnetic devices (correctors). The beam diagnostics using beam position monitors (BPMs), as well as the characterization of corrector magnets by measurement of a so-called response matrix, which are both needed for orbit correction, are routinely performed at many storage rings around the world. Furthermore, the single-particle motion (beam optics) around the closed orbit is of interest due to its implication on beam stability and performance, but could hitherto only be observed by use of additional special hardware or, in approximation, by simulations using the complete magnetic setup of the respective storage ring. It is known that response matrices hold significant information about beam optics, although in an encrypted form. As response matrices are routinely measured at many storage rings without additional hardware, their decomposition is of particular interest. In the present work, an algorithm called Closed-Orbit Bilinear-Exponential Analysis (COBEA) is being developed, with which it is possible to decompose response matrices into beam-optical information with a minimal set of assumptions. The analysis is based on a reduced and simulataneously generalized description of closed-orbit perturbations in dependence of beam parameters at monitor and corrector positions. In closing, COBEA is compared against existing measurement methods, which either need more hardware or more assumptions, and is succesfully validated against them. COBEA can therefore be used at many storage rings around the world.
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Speicherring, Teilchenstrahl, Strahloptik, Inverses Problem, Optimierungsproblem, particle accelerators, beam optics, beam diagnostics, storage rings, inverse problems, optimization problems