Real time harmonic closed orbit correction

Yu, Li Hua; Bozoki, E.; Galayda, J.; Krinsky, S.; Vignola, G.

doi:10.1016/0168-9002(89)90292-1

Cited by 32 publications

(8 citation statements)

References 3 publications

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“…In order to avoid an additional source of baseline drift in the spectra due to the thermal loading of the metallic substrate, a deposition rate of approximately one monolayer (ML) per 15 min was used. The deposition time corresponding to the completion of one fullerene monolayer was calibrated by saturating the substrate kept at or slightly above (570 K) the desorption temperature of the multilayer (455 K) [16] and measuring the ratio of the overlayer/substrate Auger peaks. Auger spectra were also collected after each IR experiment to check the fullerene coverage.…”

Section: Methodsmentioning

confidence: 99%

Vibrational dynamics of fullerene molecules adsorbed on metal surfaces studied with synchrotron infrared radiation

Rudolf

Raval

Dumas

et al. 2002

Applied Physics A: Materials Science & Processing

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Vibrational dynamics of fullerene molecules adsorbed on metal surfaces studied with synchrotron infrared radiation Rudolf, Petra; Raval, R.; Dumas, P.; Williams, G.P. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Abstract. Infrared (IR) spectroscopy of chemisorbed C 60 on Ag (111), Au (110) and Cu (100) reveals that a non-IR-active mode becomes active upon adsorption, and that its frequency shifts proportionally with the charge transferred from the metal to the molecule by about 5 cm −1 per electron. The temperature dependence of the frequency and the width of this IR feature have also been followed for C 60 /Cu (100) and were found to agree well with a weak anharmonic coupling (dephasing) to a low-frequency mode, which we suggest to be the frustrated translational mode of the adsorbed molecules.Additionally, the adsorption is accompanied by a broadband reflectance change, which is interpreted as due to the scattering of conduction electrons of the metal surface by the adsorbate. The reflectance change allows determination of the friction coefficient of the C 60 molecules, which results in rather small values (∼ 2 × 10 9 s −1 for Ag and Au, and ∼ 1.6 × 10 9 s −1 for Cu), consistent with a marked metallic character of the adsorbed molecules.Pre-dosing of alkali atoms onto the metal substrates drastically changes the IR spectra recorded during subsequent C 60 deposition: anti-absorption bands, as well as an increase of the broadband reflectance, occur and are interpreted as due to strong electron-phonon coupling with induced surface states.

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Section: Methodsmentioning

confidence: 99%

Vibrational dynamics of fullerene molecules adsorbed on metal surfaces studied with synchrotron infrared radiation

Rudolf

Raval

Dumas

et al. 2002

Applied Physics A: Materials Science & Processing

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“…Historically, four distinct methods have served the global orbit correction which include sliding bump method [6], MICADO [7], harmonic correction [8] and singular value decomposition (SVD) [5]. A variant of the SVD type correction referred to as eigenvalue decomposition has also been reported [9,10].…”

Section: Introductionmentioning

confidence: 99%

Closed orbit correction at synchrotrons for symmetric and near-symmetric lattices

Mirza

Singh

Forck

et al. 2019

Phys. Rev. Accel. Beams

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This contribution compiles the benefits of lattice symmetry in the context of closed orbit correction. A symmetric arrangement of BPMs and correctors results in structured orbit response matrices of Circulant or block Circulant type. These forms of matrices provide favorable properties in terms of computational complexity, information compression and interpretation of mathematical vector spaces of BPMs and correctors. For broken symmetries, a nearest-Circulant approximation is introduced and the practical advantages of symmetry exploitation are demonstrated with the help of simulations and experiments in the context of FAIR synchrotrons.

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“…Historically, four distinct methods have served the global orbit correction which include sliding bump method [13], MICADO [11], harmonic correction [12] and singular value decomposition (SVD) [14]. A variant of the SVD type correction referred to as eigenvalue decomposition has also been reported [37,38].…”

Section: Methods Of Correction Calculation For Correctorsmentioning

confidence: 99%

“…Harmonic correction was the first method to discuss the notion of mode-based correction by means of a decomposition of the perturbed orbit into Fourier harmonics which can be corrected individually. The technique is primarily based upon the work of L.H.YU and co-authers at BNL US [12], where they introduced the Courant-Snyder variables in Eq. 2.11 as,…”

Section: Harmonic Correctionmentioning

confidence: 99%

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Closed orbit feedback system for the fast ramping hadron synchrotrons

Mirza¹

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The realization of a fast and robust closed orbit feedback (COFB) system for the on-ramp orbit correction at SIS18 synchrotron of FAIR project is reported in this thesis. SIS18 has some peculiar behaviors including on-ramp optics variation, very short lengths of the ramps (200 ms to 1 s) and a cycle-to-cycle variation of beam parameters. The realized fast COFB system being robust against above mentioned features of SIS18 is a first of its kind and the course to its realization led to some novel contributions in the field of closed orbit correction. A new method relying on the discrete Fourier transform (DFT)-based decomposition of the orbit response matrix (ORM) has been introduced, exploiting the symmetry in the arrangement of beam position monitors (BPMs) and the corrector magnets in the synchrotrons. A nearest-circulant approximation has also been introduced for synchrotrons having slight deviation from the symmetry, making the method applicable to a vast majority of synchrotrons. Moreover, the performance and the stability analysis of COFB systems in the presence of ORM mismatch between the synchrotron and the feedback controller is presented. The COFB systems are divided into slow and fast regimes and a new stability criterion consistent with measurements, is introduced. The practicality of the criterion is verified experimentally at COSY Jülich and is used for the analysis of various sources of ORM mismatch at SIS18. The commissioning of the SIS18 COFB system is also reported in detail which relies on Libera Hadron as the main hardware resource for the controller implementation. The on-ramp orbit correction is demonstrated for the horizontal plane of SIS18, for the disturbance rejection up to 600 Hz.

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Real time harmonic closed orbit correction

Cited by 32 publications

References 3 publications

Vibrational dynamics of fullerene molecules adsorbed on metal surfaces studied with synchrotron infrared radiation

Vibrational dynamics of fullerene molecules adsorbed on metal surfaces studied with synchrotron infrared radiation

Closed orbit correction at synchrotrons for symmetric and near-symmetric lattices

Closed orbit feedback system for the fast ramping hadron synchrotrons

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