| Paper | Title | Page |
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| THPCH078 | Successful Bunched-Beam Stochastic Cooling in RHIC | 2967 |
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| Stochastic Cooling of high energy and high frequency bunched beam has been demonstrated in RHIC at 100 GeV. Narrowing of the Schottky spectrum and shorting of the bunch length resulted from cooling the beam for 90 minutes. The purpose of the stochastic cooling is to counteract the fundamental limit of the luminosity lifetime of heavy ions in RHIC which is Intra-Beam Scattering. IBS drives transverse emittance growth and longitudinal de-bunching. The major components of the system have been tested with heavy ion and proton beams in previous runs in RHIC, demonstrating that the difficult challenges of high frequency bunched beam stochastic cooling can be overcome. The vexing problem of pollution of the Schottky spectrum by coherent components is solved with optimized filtering and high dynamic range low noise electronics. A set of 16 high-Q cavities is used to achieve adequate kicker voltage in the 5 to 8 GHz band. This technique exploits the bunched beam time structure to level the microwave power requirement and enables the use of solid state amplifiers to drive the kickers. Because RHIC did not operate with heavy ions in the FY06 run, the system was tested with specially prepared low intensity protons bunches of 2·109 particles. | ||
| THPCH082 | Broadband Bunch by Bunch Feedback for the ESRF using a Single High Resolution and Fast Sampling FPGA DSP | 2976 |
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| In order to increase the current in the ESRF storage ring we have developed a set of multibunch feedback systems aimed at fighting longitudinal and transverse coupled bunch instabilities. The longitudinal feedback (LFB) has been the first system installed and tested. It was designed using the scheme developed at SLAC, ALS and INFN Frascati: bunch by bunch processing of a beam phase error signal and correction using a low Q kicker driven by a QPSK modulator. However, we took advantage for this development of the latest available technology for the signal processing electronics with high resolution, high sampling rate ADC and DAC, and FPGA DSP, as well as for the FPGA programming environment. It allowed us to substantially reduce the complexity: the algorithm runs on a single processor, the kicker requires only 200W of RF power to control a 6GeV beam, and the implementation took only about one year. We will describe the main features of our LFB and present the results already achieved in the damping of instabilities driven by our RF cavity HOM. We will also report on the status of the transverse feedback, which is being built up using the same FPGA system as the longitudinal one. | ||
| THPCH083 | A Tune Feedback System for the HERA Proton Storge Ring | 2979 |
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| The transverse tunes of an accelerator or storage ring are important parameters which have to be controlled and adjusted continuously during beam operation in order to assure good experimental background conditions. For the HERA proton storage ring, persistent current effects of the superconducting magnets are the main source for the inadequate repeatability of the tunes without a feedback while the proton beam is accelerated. A tune feedback has been developed, implemented and tested during beam acceleration and luminosity operation. Considering the different conditions during energy ramps and luminosity runs two versions of this feedback system have been established based on different correction and peak-finding algorithms (e.g. wavelet analysis). No additional excitation is needed on top of the standard tune indication system in HERA. The tunes could be kept constant during beam accceleration with a standard deviation of delta Q = 0.003. In luminosity runs where the tune control is more critical, first tests resulted in a standard deviation which was a factor of ten smaller. The feedback system is implemented as a standard tool for beam acceleration. | ||
| THPCH084 | Control Path of Longitudinal Multibunch-feedback System at HERA-p | 2982 |
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| A longitudinal broadband damper system to control coupled bunch instabilities has been developed and installed in the proton accelerator HERA-p at the DESY. The control system consists of a control path and a Fast Diagnostic System (FDS) for oscillation diagnostic. The control path consists of FPGA-based digital controller, vector modulator, 1kW power amplifier, kicker-cavity and beam. In the FDS, the bunch phase signals are sampled by a digital FPGA board with 14Bit ADC (controller) with a sampling frequency of 10.4MHz. Phase calculation for all bunches and offset correction will be done by FPGA software which includes a digital filter. The filter has to be able to deal with a slowly changing synchrotron frequency. Here we consider a filter design which treats each of maximum 220 bunches as an independent oscillator which has to be damped. More sophisticated mode filter algorithms may be required to get better noise performance. The FPGA-board output signal modulates a 104 MHz sine-wave. The resulting logitudinal correction kick signal is provided by the kicker-cavity. Beside the technical details we present first operational experience and the actual system performance. | ||
| THPCH085 | The Longitudinal Coupled Bunch Feedback for HERA-p | 2985 |
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| A longitudinal broadband damper system to control coupled bunch instabilities has recently been constructed and installed in the 920~GeV proton accelereator HERA-p at the Deutsches Elektronen-Synchrotron DESY. This represents one of the attempts to increase the specific luminosity at HERA by reducing the bunch length. The final bunch length is defined by the initial emittance after injection and by the acceleration process where multiply occuring coupled bunch instabilities provoke bunch length blow up at discrete energies during the ramp. The actual feedback design consists of a fast, high precision bunch centroid phase detector, a 1~kW feedback cavity with 104~MHz centre frequency and 8~MHz bandwidth (FWHM), a I/Q-vector modulator, the low level digital FPGA-board with 14 Bit ADCs and DACs and a cavity transient diagnostics. The system measures the phases of all bunches and calculates corrections in real time (bunch spacing: 96~ns) which are then applied to the beam via a longitudinal kicker. The filter deals with a slowly changing synchrotron frequency (20-80 Hz). | ||
| THPCH086 | Design of a Local IP Orbit Feedback at HERA-e | 2988 |
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| At the electron-proton collider HERA it is often observed that the proton emittance growth rate of colliding bunches is larger compared to non-colliding proton bunches. In addition the proton background rates are increasing when the two beams are brought into collision. There are indications that a contribution comes from closed orbit oscillations of the electron beam at the two IPs. In the arcs of HERA-e oscillation amplitudes of 100-200 micrometer with frequencies of 2-15 Hz and harmonics of 50 Hz are observed. In order to stabilize the orbit at the IPs in both planes a local digital orbit feedback system with a bandwidth of more than 20 Hz has been developed. The beam position at the IPs is measured with BPMs using dedicated electronics. The four local orbit bumps are produced by air-coil steerer magnets. The data are transmitted using SEDAC field bus lines to a central PC, which is used for the computation of the correction. | ||
| THPCH087 | Design and Operation of a Ferrite Loaded Kicker Cavity for the Longitudinal Coupled Bunch Feedback for HERA-p | 2991 |
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| A longitudinal broadband damper system to control coupled bunch instabilities has recently been constructed and installed in the 920 GeV proton accelereator HERA-p at the Deutsches Elektronen-Synchrotron DESY. The goal of this system is to reduce the bunch length and thus increase specific luminosity at HERA-p. Within the control system a kicker cavity is used as an actuator. The original aspect of this cavity lies in the simple geometry with no need for vacuum inside the cavity and high shunt impedance despite an internal ferrite load. The ferrite load is succesfully used to dampen higher order modes down to Q < 50 while the fundamental mode is damped by less than 2 dB. While nominal input power is rated at 60 dBm the cavity is prepared to handle beam loading. In spite of power requirements and ferrite load the cavity needs no active cooling. It can be tuned in center frequency and bandwidth over a range of 96..105 MHz and 4..7 MHz respectively and in consequence provides an optimal actuator for the particle beam control system. Presented will be the design details, all relevant parameters, the design of the internal ferrite load and operational experience. | ||
| THPCH088 | A Possibility of Constant Energy Extraction at the KEK ATF2 | 2994 |
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| Beam energy oscillations of the order of 0.02% take place at the KEK ATF. With extractions, the synchrotron oscillation amplitude and phase at the extraction turn randomly fluctuates. The energy jitter causes a position/angle jitter in the Diagnostic section of the Extraction Line. To reduce it, a feed forward energy stabilisation can be used done by extraction of the beam at the turn next to that turn at which the energy passes the equilibrium value. For this, the synchrotron oscillation is measured by a turn-by-turn BPM as a horizontal position oscillation. A fast turn-by-turn processor detects the turn where the oscillation passes zero, and generates an extraction permission signal that triggers the existing ATF Extraction system. Stability improvement by factor of 10 can be obtained even when the extraction is done with uncertainty up to three turns after the trigger. | ||
| THPCH089 | The Electromagnetic Background Environment for the Interaction-point Beam Feedback System at the International Linear Collider | 2997 |
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| The Interaction Point (IP) feedback system is essential for maintaining the luminosity at the International Linear Collider (ILC). It is necessary to demonstrate the performance of the feedback beam position monitor (BPM) in an electron-positron pair background similar to that expected in the ILC interaction region (IR). We have simulated the ILC beam-beam interactions and used a GEANT model of the IR to evaluate the pair and photon flux incident on the BPM, for both the 2 mrad and 20 mrad crossing angle geometries. We present results as a function of the proposed machine parameter schemes, as well as for various system layouts within the IR. We plan to study the degradation of BPM resolution, and the long term survivability, in beam tests at End Station A at SLAC. To simulate the background environment of the ILC a 'spray beam' will be produced, which will scatter from a mechanical mock-up of the forward region of the IR, and irradiate the BPM with realistic flux of secondary pairs. We present the proposed experimental layout and planned beam tests. | ||
| THPCH090 | Stabilization of the ILC Final Focus Using Interferometers | 3000 |
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| We are developing a system of interferometers that can measure the relative motion between two objects (such as the two final focus quadrupoles) to a few nanometers using interferometric methods. Two instruments are developed at the John Adams Institute at University of Oxford: A distance meter to measure length changes and a straightness monitor to measure perpendicular shifts. We will present technique, results and resolutions of our distance meter prototype. We will also examine their applications at the ILC. | ||
| THPCH091 | Status of the ELETTRA Global Orbit Feedback Project | 3003 |
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| A fast digital feedback system is under development to stabilize the electron beam closed orbit at the ELETTRA storage ring in the band up to 300 Hz. In view of the implementation of the feedback, the existing orbit measurement system will be upgraded to allow for better accuracy in the beam position measurement and higher acquisition rate. A global correction algorithm running on a number of distributed processing units will correct the orbit using all of the storage ring steerer magnets. The status of the project development is given in this article. | ||
| THPCH092 | Single-loop Two-dimensional Transverse Feedback for Photon Factory | 3006 |
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| We installed a 500MS/s single-loop two-dimensional transverse bunch-by-bunch feedback system in the Photon Factory ring at KEK and the system is in operation at its user mode. The system composed of a single feedback loop; one skewed pair of BPM electrodes and one kicker stripline at skewed position to detect position and kick horizontally and vertically with a single signal line, and a SPring-8 feedback processor. Consequently, this system is easy to tune and cost effective. SPring-8 feedback processor employs FPGA that has enough computing power for processing more than 20-tap FIR filter required for newly developed two-dimensional feedback signal processing. We report the principle of the system, the result of test and the experience. | ||
| THPCH093 | Bunch-by-bunch Feedback for the Photon Factory Storage Ring | 3009 |
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| After the straight-section upgrade in 2005, the PF (Photon Factory) ring will start the top-up operation or the continuous mode in 2006. Previously the octupole magnets were used to suppress the transverse coupled bunch instability and RF modulation method to enhance the bunch length has been effectively used to suppress the longitudinal instabilities. However, such kind of methods are not suitable for the top-up operation, we are preparing active bunch-by-bunch feedback systems for both transverse and longitudinal plane. The transverse feedback system has been installed along with the straight-section upgrade, this system uses a FPGA based feedback processor board developed at the SPring-8, both horizontal and vertical signals are processed in a single control loop. For the longitudinal feedback, a two-port DAFNE type wide-band cavity has been designed and is now manufacturing, a digital signal processing part is under design, the whole system will start commissioning in autumn 2006. | ||
| THPCH094 | Fully Digitized Synchronizing and Orbit Feed-back Control System in the KEK Induction Synchrotron | 3012 |
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A concept of "Induction Synchrotron", where an extremely long bunch captured by the step barrier-voltages is accelerated with the induction accelerating voltage, is being to be fully demonstrated in the KEK 12GeV-PS for the first time*. Attractive applications of the induction synchrotron are such as higher intensity proton drivers, future high luminosity hadron colliders with superbunch, and arbitral-ion accelerators. Synchronization between the voltage-pulse generation and the beam circulation, accelerating voltage control, and beam-orbit control without beam-rf phase, which is analogous to Delta-R feedback in an RF synchrotron, are indispensable in the induction synchrotron. A fully digitized real-time pulse density and discrete timing control system with 1GHz DSPs has been newly developed. Notable characteristics of the control system, some of which are synchronization at 1MHz revolution frequency with 8ns timing accuracy, are explained in detail. Experimental results of the induction acceleration with the digital orbit controller are also presented in this paper.
*K. Torikai et al. "Acceleration and Confinement of a Proton Bunch with the Induction Acceleration System in the KEK Proton Synchrotron", submitted to Phys.Rev.ST-AB(2005), KEK-Preprint 2005-80. |
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| THPCH095 | Transverse Damping System at SIS100 | 3014 |
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| The basic concept and main design features of the transverse damping system at the SIS100 synchrotron are presented. SIS100 with five times the circumference of the current SIS18 accelerator is a part of the Facility for Antiproton and Ion Research (FAIR) which is the next accelerator complex being constructed on the GSI site. The existing GSI accelerators serve as injector for SIS100. The SIS100 synchrotron will provide ion beams of high intensities which can lead to transversal and longitudinal beam instabilities. In order to damp the coherent transverse beam oscillations, a transverse feedback system (TFS) is going to be implemented in SIS100. The TFS presented is a feedback with a real-time digital signal processing for damping of transverse injection oscillations, feedback curing transverse coupled bunch instabilities, and excitation of transverse oscillations for beam measurements and other applications. The data on the bandwidth and gain of the TFS as well as the general description of the central processing unit are presented. | ||
| THPCH096 | Intra Bunch Train Feedback System for the European X-FEL | 3017 |
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| After joining the preparatory phase of the European X-FEL project, the Paul Scherrer Institut (PSI) agreed in taking over responsibility for electron beam stabilization by developing a fast intra bunch train feedback (IBFB) system, which will be tested in its prototype version at the VUV-FEL facility at DESY. The IBFB will make use of the long bunch trains provided by the superconducting drive accelerators of the VUV- as well as the European X-FEL allowing to damp beam motions in a frequency range of a few kHz up to several hundreds of kHz applying modern control algorithms in a feedback loop. The FPGA-based, digital data processing and the low latency time (preferably < 200 ns) permit the elimination of long range (from bunch train to bunch train) and ultra fast (bunch by bunch) repetitive beam movements by adaptive feed forwards. In this paper, we will introduce the IBFB design concept and report on first test measurements with newly designed stripline beam position monitors for the VUV-FEL. | ||
| THPCH097 | Commissioning of the Digital Transverse Bunch-by-bunch Feedback System for the TLS | 3020 |
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| Multi-bunch instabilities degrade the beam quality leading to increased beam emittance, energy spread or even to beam loss. The feedback system is used to suppress multi-bunch instabilities due to resistive wall of the beam ducts, cavity-like structures and trapped ions. A new digital transverse bunch-by-bunch feedback system was commissioned at the Taiwan Light Source recently, and has replaced the previous analog system. The new system has the advantages that it enlarges the tune acceptance compared with the old system, enhances damping for transverse instability at high current, and as a result, top-up operation was achieved. In this new system, a single feedback loop simultaneously suppresses both the horizontal and vertical multi-bunch instabilities. The feedback system employs the latest generation FPGA feedback processor to process bunch signals. Memory installed to capture up to 250 msec bunch oscillation signal has included the considerations for system diagnostic and should be able to support various beam physics study. | ||
| THPCH098 | FPGA-based Longitudinal Bunch-by-bunch Feedback System for TLS | 3023 |
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| A FPGA Based Longitudinal Bunch-by-Bunch Feedback System for TLS is commissioning recently to suppress strong longitudinal oscillation. The system consists of pickup, Bunch oscillation detector, FPGA based feedback processor borrow form the design of Spring8. Modulator converts the correction signal to the carrier frequency and longitudinal kicker which was re-designed form SLS' and working at 1374 MHz. The feedback processor is based upon latest generation FPGA feedback processor to process bunch signals. The memory capture is up to 250 msec bunch oscillation signal. The software and hardware design are also included for system diagnostic and support various beam physics study. Preliminary commission result will be summaried in this report. | ||
| THPCH099 | A Turn-by-turn, Bunch-by-bunch Diagnostics System for the PEP-II Transverse Feedback Systems | 3026 |
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| A diagnostics system centered around commercial fast 8-bit digitizer boards has been implemented for the transverse feedback systems at PEP-II. The boards can accumulate bunch-by-bunch position data for 4800 turns (35 ms) in the x plane and the y plane. A dedicated trigger chassis allows to trigger the data acquisition on demand, or on an injection shot to diagnose injection problems, and provides gating signals for grow-damp measurements. Usually, the boards constantly acquire data and a beam abort stops data acquitision, thus preserving the last 4800 turns of position information before a beam abort. Software in a local PC reads out the boards and transfers data to a fileserver. Matlab-based data analysis software allows to present the raw data but also higher-level functions like spectra, modal analysis, spectrograms and other functions. The system has been instrumental in diagnosing beam instabilities in PEP. This paper will describe the architecture of the system and its applications. | ||
| THPCH100 | New Fast Dither System for PEP-II | 3029 |
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| The PEP-II B-Factory uses multiple feedback systems to stabilize the orbits of its stored beams and to optimize their performance in collision [1]. This paper describes an upgrade to the feedback system responsible for optimizing the overlap of colliding beams at the interaction point (IP). The effort was motivated by a desire to shorten the response time of the feedback, particularly in the context of machine-tuning tasks. We describe the original feedback system, the design for the new one, and give a status report on the installation. | ||
| THPCH101 | Modeling and Simulation of Longitudinal Dynamics for LER-HER PEP II Rings | 3032 |
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| A time domain dynamic model and simulation tool for beam-cavity interactions in LER and HER rings at PEP II is presented. The motivation for this tool is to explore the stability margins and performance limits of PEP II LLRF systems at higher currents and upgraded RF configurations. It also serves as test bed for new control algorithms and to define the ultimate limits of the architecture. The tool captures the dynamical behavior of the beam-cavity interaction based on a reduced model. It includes nonlinear elements in the klystron and signal processing. The beam current is represented by macro-bunches. Multiple RF stations in the ring are represented via one or two single macro-cavities. Each macro-cavity captures the overall behavior of all the 2 or 4 cavity RF stations. This allows modeling the longitudinal impedance control loops interacting with the longitudinal beam model. Validation of simulation tool is in progress by comparing the measured growth rates for both LER and HER rings with simulation results. The simulated behavior of both machines at high currents are presented comparing different control strategies and the effect of non-linear klystrons and the linearizer. | ||
| THPCH102 | Fast Global Orbit Feedback System in SPEAR3 | 3035 |
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| New digital global orbit feedback system is under commissioning in SPEAR3 light source. The system has 4kHz sampling rate and 200Hz bandwidth. Correction algorithm is based on Singular Value Decomposition (SVD) of the orbit response matrix. For performance tuning and additional flexibility when adding or removing correctors and BPMs, we implemented an independent PID control loop for every orbit eigenvector used. This paper discusses performance of the new system and some advantages of multiple PID loops in the eigenvector space versus a single PID loop working on the raw orbit error. | ||
| THPCH103 | Design and Testing of Gproto Bunch-by-bunch Signal Processor | 3038 |
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| A prototype programmable bunch-by-bunch signal acquisition and processing channel with multiple applications in storage rings has been developed at SLAC. The processing channel supports up to 5120 bunches with bunch spacings as close as 1.9 ns. The prototype has been tested and operated in five storage rings: SPEAR-3, DAFNE, PEP-II, KEKB, and ATF damping ring. The testing included such applications as transverse and longitudinal coupled-bunch instability control, bunch-by-bunch luminosity monitoring, and injection diagnostic. In this contribution the prototype design will be described and its operation will be illustrated with the data measured at the abovementioned accelerators. | ||
| THPCH104 | Design and Simulation of the ILC Intra-train Orbit and Luminosity Feedback Systems | 3041 |
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To maintain luminosity to within a few percent of the design at the International Linear Collider (ILC), beam stability at the IP needs to be maintained at the sub-nanometre level. To achieve the beam stability required in the presence of ground motion, multiple feedback systems are required. The baseline design calls for a 5-Hz system to control the orbit in the Linac and Beam Delivery System (BDS) and an intra-train system to address high-frequency ground motion and mechanical disturbances which cause orbit distortions at the IP between pulses enough to completely destroy the luminosity. Details of the slower feedback systems have been addressed elsewhere*. The detailed design and simulation of the intra-train feedback systems are described here. This system controls the vertical position and angle at the IP such that luminosity is maximised. The system brings the beams into collision based on BPM-derived information from the initial bunches of the train. It then tunes the IP collision parameters (both position and angle) based on a fast (bunch-by-bunch) luminosity signal from the BeamCal. The system is implemented in fast digital FPGA logic, designed using Matlab's Simulink.
*A. Seryi et al. "Issues of Stability and Ground Motion in ILC", Nanobeam 2005.**G. White et al. "Multi-Bunch Simulations of the ILC for Luminosity Performance Studies", PAC2005. |
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| THPCH105 | Summary of Coupling and Tune Feedback Results during RHIC Run 6, and Possible Implications for LHC Commissioning | 3044 |
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| Efforts to implement tune feedback during the acceleration ramp in RHIC have been hampered by the effect of large betatron coupling, as well as by the large dynamic range required by transition crossing with ion beams. Both problems have been addressed, the first by implementation of continuous measurement of coupling using the phase-locked tune meter, and the second by the development of the direct diode detection analog front end. Performance with these improvements will be evaluated during the first days of RHIC Run 6 beam commissioning. With positive results, the possibility of implementing operational feedback control of tune and coupling during beam commissioning will be considered. After beam commissioning, chromaticity feedback will be explored as a part of the accelerator physics experimental program. We will summarize the results of these investigations, and discuss possible implications of these results for LHC commissioning. |