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| TUPB22 | Renewal of BPM Electronics of SPring-8 Storage Ring | storage-ring, controls, closed-orbit, emittance | 114 | ||
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The signal processing electronics of the SPring-8 Storage Ring BPM were replaced during the summer shutdown period of the year 2006. Since then, the new electronics have been put into operation for user experiment runs. The purpose of the renewal was to upgrade the performance of the position measurement system, i.e. the position resolution, speed of the measurement, etc. The position resolution of them in the real operation condition was estimated by using the stored beam in the same condition as the operations for user experiments, in the following way. The closed orbit distortions (COD) were repeatedly measured with the interval of 4 seconds in order to obtain the root mean square (r.m.s.) values of differences between two consecutive measurements. Since the obtained r.m.s. values included the intrinsic resolution of the position measurement system and the effect of the beam motion, the effect of the beam motion was separated from the obtained r.m.s. data by assuming that the effect of the beam motion was proportional to the betatron function values at the BPM locations. As a result, the intrinsic resolution was estimated to be 0.1μmeters.
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| WEPB06 | Direct Comparison of the Methods of Beam Energy Spread Determination in the VEPP-4M Collider | collider, diagnostics, electron, photon | 244 | ||
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The VEPP-4M electron-positron collider is now operating with the KEDR detector for the experiment of precise measurement of tau-lepton mass. The nearest experimental program of the accelerator includes scan of the energy area below J/psi meson to search narrow resonances. The monitoring of beam energy spread is important to know the energy spread contribution into the total systematic error. In this report we discuss the application of several diagnostics for beam energy spread measurement. The data obtained with Compton BackScattering (CBS) technique* are compared with the value of the spread derived from the betatron motion of the beam**. The measurements by all the methods were done at the same accelerator run, i.e. the different diagnostics can be compared directly. The value of the energy spread was determined for a set of collider operating modes, covering the energy area from 1200 MeV up to 1843 MeV. Width of the J/psi and psi' resonance measured with the KEDR detector is used as a reference.
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References*N. Muchnoi et al. //Proceed. of EPAC 2006, Edinburg, Scotland, TUPCH074**T. Nakamura et al. // Proceed. of the 2001 Particle Accelerator Conference, Chicago, p. 1972-1974. |
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| WEPB21 | Kicker Based Tune Measurement for DELTA | kicker, storage-ring, feedback, resonance | 277 | ||
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We have set up a tune measurement for the electron storage ring Delta based on broadband beam excitation with a kicker magnet and measurement of the relaxation betatron oscillations turn-by-turn. By averaging over several kicks the kick amplitude may be as low as 600 nrad in standard user runs at nominal current, leading to negligible beam distortion. Signal to noise ratios in excess of 10 are reliably achieved down to 200 uA beam current using a maximum kicker amplitude of 10 urad. A simple tune feedback algorithm compensates for tune shifts due to vacuum chamber movement and orbit movement in sextupoles.
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| WEPC04 | Transverse Feedback Development at SOLEIL | feedback, impedance, damping, emittance | 316 | ||
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The SOLEIL ring is planned to operate in both multibunch and high current per bunch modes. However, the small vertical chamber aperture around the SOLEIL ring enhances the transverse impedance both in its resistive-wall and broadband content, resulting in instabilities that appear at relatively low current compared to the desired values. A decision was therefore taken to install a digital bunch-by-bunch feedback system, with an aim to make it operational from the beginning of the user operation. The system implemented comprises components developed elsewhere, particularly the FPGA processor of Spring-8, chosen among different possible solutions. Using a BPM and a stripline in the diagonal mode, a single unit of the FPGA processor board has shown to successfully suppress resistive-wall and ion induced instabilities in either one or both transverse planes up to 300 mA. The paper discusses the system characteristics including striplines whose shunt impedance was maximised by keeping the coupling impedance small*, the obtained performance as well as future extensions to overcome the encountered limitations.
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* C. Mariette ID1209 |
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| WEPC10 | Tune, Coupling, and Chromaticity Measurement and Feedback During RHIC Run 7 | feedback, injection, coupling, controls | 331 | ||
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Tune feedback was first implemented in RHIC in 2002, as a specialist activity. The transition to full operational status was impeded by dynamic range problems, as well as by overall loop instabilities driven by large coupling. The dynamic range problem was solved by the CERN development of the Direct Diode Detection Analog Front End[1]. Continuous measurement of all projections of the betatron eigenmodes made possible the world's first implementation of coupling feedback during beam acceleration, resolving the problem of overall loop instabilites[2,3]. Simultaneous tune and coupling feedbacks were utilized as specialist activities for ramp development during the 2006 RHIC run. At the beginning of the 2007 RHIC run there remained two obstacles to making these feedbacks fully operational in RHIC - chromaticity measurement and control, and the presence of strong harmonics of the power line frequency in the betatron spectrum. Preliminary investigations of power line harmonics were presented earlier[4]. We report here on progress in tune, coupling, and chromaticity measurement and feedback, and discuss the relevance of our results to the LHC commissioning effort.
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[1] M. Gasior and R. Jones, DIPAC 2005, Lyon, p.312.[2] P. Cameron et. al., PRST-AB, Dec 2006. [3] R. Jones et. al., DIPAC 2005, Lyon, p.298.[4] P. Cameron et. al., DIPAC 2005, Lyon, p.33. |
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| WEPC26 | Transverse Bunch-by-Bunch Feedback for the VEPP-4M Electron-Positron Collider | feedback, kicker, coupling, impedance | 367 | ||
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Transverse mode coupling instability (TMCI or fast head-tail) is the principal beam current limitation of the VEPP-4M electron-positron collider. For the high-energy physics experiments at the 5.5 GeV energy, the VEPP-4M bunch current should exceed much the TMCI threshold. To suppress transverse beam instabilities, a broadband bunch-by-bunch digital feedback system is developed. The feedback concept is described, the system layout and first beam measurements are presented.
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