Instabilities and Feedback

Feedback Systems and Technology

Paper Title Page
MPPP001 A Vertical Multi-Bunch Feedback System for ANKA 761
  • P. Wesolowski, I. Birkel, E. Huttel, A.-S. Müller, M. Pont, F. Pérez
    FZK, Karlsruhe
  ANKA is a synchrotron light source with a top energy of 2.5 GeV. The maximum electron current at ANKA is presently limited by multi-bunch instabilities to 200 mA. In order to overcome this barrier a transverse analog multi-bunch feedback system is presently being commissioned. A BPM is used for beam detection. The vertical position signal passes a notch filter, is amplified, and subsequently fed to a vertical beam kicker. The present paper shows the layout of ANKA feedback system and discusses the first results of its operation.  
MPPP002 Stochastic Cooling Electrodes for a Wide Velocity Range in the CR 799
  • F. Nolden, B.  Franzke, C. Peschke
    GSI, Darmstadt
  • M.C. Balk, R. Schuhmann, T. Weiland
    TEMF, Darmstadt
  • F. Caspers, L. Thorndahl
    CERN, Geneva
  The CR storage ring is part of the FAIR project at GSI. It serves as a first stage of stochastic cooling for secondary rare isotopes at v/c=0.83 as well as for antiprotons at v/c=0.97. To avoid the installation of dedicated structures for each kind of beam, electrodes have been developed which are usable for both beams. They are based on slotline structures mounted perpendicular to the beam. They are shorted at the ends, and their signal is extracted by two striplines on the rear side, placed a quarter wavelength away from the open ends. The width of the structures can be adjusted to the initial betatron oscillation amplitudes. Their length is 24 mm, and the signal from many of these structures mounted in a row can be combined. The signal combination can be matched to the different beam velocities. The paper shows results from field calculations, prototype tests, and estimates of the signal combination efficiency. The beam impedance of the novel structures is compared with the superelectrodes applied in the former CERN AC and with the slow-wave structures currently installed in the FNAL Debuncher.  
  • H.-S. Kang, J. Choi, M.-H. Chun, K.M. Ha, J.Y. Huang, Y.-C. Kim, E.-H. Lee, T.-Y. Lee, W.W. Lee, J.-H. Suh
    PAL, Pohang, Kyungbuk
  Funding: Ministry of Science and Technology, Korea.

A slow global orbit feedback (SOFB) is routinely operating in the usual user service operation at PLS. The orbit feedback uses 22 correctors in each plane which have 20-bit capability for the vertical plane and 16-bit capability for the horizontal plane, and the feedback speed is 4 seconds. The orbit stability in RMS was maintained below 1 mm in both planes for one hour and 3 mm for a 12-hour operation. The BPM chamber movement due to the change of synchrotron radiation heat load mainly limits the SOFB performance. The intensity dependence of BPM electronics is well compensated by a look-up table of BPM.

MPPP004 LHC Orbit Stablisation Tests at the SPS 886
  • R.J. Steinhagen, J. Andersson, L.K. Jensen, O.R. Jones, J. Wenninger
    CERN, Geneva
  The LHC presently build at CERN is the first proton collider that requires a continuous orbit control for safe and reliable machine operation. A realistic test of the orbit feedback system has been performed in 2004 using already present LHC instrumentation and infrastructure on a 270 GeV coasting beam in the SPS. It has been demonstrated that the chosen feedback architecture can stabilise the beam better than 10 micrometre and is essentially limited by the noise of the beam position monitor and the bandwidth of the corrector magnets. The achieved orbit stability is comparable to those found at modern light sources and gives enough operational margin with respect to the requirements of the LHC Cleaning System (70 micrometre). Estimates for the long term drifts and achievable stability will be presented based on the experimental results.  
MPPP005 A New Kicker for the TLS Longitudinal Feedback System 949
  • W.K. Lau, L.-H. Chang, C.W. Chen, H.Y. Chen, P.J. Chou, K.-T. Hsu, S.Y. Hsu, T.-T. Yang
    NSRRC, Hsinchu
  • M. Dehler
    PSI, Villigen
  A new longitudinal kicker that is modified from the Swiss Light Source (SLS) design to fit into the TLS storage ring. It will be served as the actuator in the longitudinal multi-bunch feedback control loop. Beam coupling impedance has been calculated by Gdfidl with a PC cluster. Previous to the installation of this new kicker, bench measurement has been performed in the laboratory to characterize this new kicker. The experimental setups for bandwidth and coaxial wire measurement of longitudinal coupling impedance and their corresponding test results will be reported. As a cross check, bead-pull measurement has also been done to verify the beam coupling measurement by coaxial wire method at the kicker center frequency. Longitudinal field profile of the accelerating mode along the beam path has also been mapped. High order cavity modes of the kicker have also been observed and their effects on the beam are evaluated.  
MPPP006 Performance Calculation on Orbit Feedback for NSLSII 1036
  • L.-H. Yu
    BNL, Upton, Long Island, New York
  We discuss the preliminary calculation on the performance of closed orbit feedback system for NSLSII, its relation to the requirement on BPM, floor and girder stability, power supply stability, etc.  
MPPP007 Operating Performance of the Low Group Delay Woofer Channel in PEP-II 1069
  • D. Teytelman, J.D. Fox, D. Van Winkle
    SLAC, Menlo Park, California
  Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515.

In PEP-II collider a dedicated low group-delay processing channel has been developed in order to provide high damping rates necessary to control the fast-growing longitudinal eigenmodes driven by the fundamental impedances of the RF cavities. A description of the digital processing channel operating at 9.81 MHz and capable of supporting finite impulse response (FIR) controllers with up to 32 taps will be presented. A prototype system has been successfully commissioned in the High-Energy Ring (HER) in May 2004. Operating experiences with the prototype and the newly determined limits on achievable longitudinal damping will be discussed and illustrated with experimental data.

MPPP009 Linac Coherent Light Source Longitudinal Feedback Model 1156
  • J. Wu, P. Emma, L. Hendrickson
    SLAC, Menlo Park, California
  Funding: Work is supported by the US Department of Energy under contract DE-AC02-76SF00515.

The Linac Coherent Light Source (LCLS) will be the world's first x-ray free-electron laser (FEL). To ensure the vitality of FEL lasing, it is critical to preserve the high quality of the electron beam during acceleration and compression. The peak current and final energy are very sensitive to system jitter. To minimize this sensitivity, a longitudinal feedback system on the bunch length and energy is required, together with other diagnostics and feedback systems (e.g., on transverse phase space). In this paper, we describe a simulation framework, which includes a realistic jitter model for the LCLS accelerator system, the RF acceleration, structure wakefield, and second order optics. Simulation results show that to meet the tight requirements set by the FEL, such a longitudinal feedback system is mandatory.

MPPP010 Feedback to Suppress Phase Noise at Aladdin 1180
  • R.A. Bosch, K. Jacobs, K. J. Kleman
    UW-Madison/SRC, Madison, Wisconsin
  The performance of the Aladdin infrared beamline is adversely affected by a Robinson mode in which all bunches move in unison with a frequency of 3 kHz. To decrease these oscillations, feedback has been installed in the radiofrequency system to damp longitudinal motion of the bunch centroids. Simulations indicate that at frequencies around 3 kHz, the phase noise generated by Robinson modes may be reduced 20 dB by feedback with a damping time of 0.3 ms. This agrees with the measured performance of feedback circuitry. Since the feedback greatly improves operation of the infrared beamline, it is now incorporated into the standard operation of Aladdin.  
MPPP011 Fermilab Recycler Damper Requirements and Design 1239
  • J.L. Crisp, M. Hu, V. Tupikov
    Fermilab, Batavia, Illinois
  The design of transverse dampers for the Fermilab Recycler storage ring is described. An observed instability and analysis of subsequent measurements are used to identify the requirements. The digital approach being mplemented is presented.  
MPPP012 First-Principles Simulation and Comparison with Beam Tests for Transverse Instabilities and Damper Performance in the Fermilab Main Injector 1300
  • D.J. Nicklaus, G.W. Foster, V.S. Kashikhin
    Fermilab, Batavia, Illinois
  An end-to-end performance calculation and comparison with beam tests was performed for the bunch-by-bunch digital transverse damper in the Fermilab Main Injector. Time dependent magnetic wakefields responsible for "Resistive Wall" transverse instabilities in the Main Injector were calculated with OPERA-2D using the actual beam pipe and dipole magnet lamination geometry. The leading order dipole component was parameterized and used as input to a bunch-by-bunch simulation which included the filling pattern and injection errors experienced in high-intensity operation of the Main Injector. The instability growth times, and the spreading of the disturbance due to newly mis-injected batches was compared between simulations and beam data collected by the damper system. Further simulation models the effects of the damper system on the beam.  
MPPP013 Stabilizing Low Frequency Beam Motion in the Tevatron 1353
  • V.H. Ranjbar
    Fermilab, Batavia, Illinois
  Funding: Operated by Universities Research Association Inc. under Contract No. DE-AC02-76CH03000 with the United States Department of Energy.

A feed back orbit stabilization system has been developed using a set of BPMS and existing Tevatron corrector magnets to stabilize beam motion up to 50 microns below 25 Hz. The construction of this system is described and the stability limits and magnitude of beam motion reduction is explored.

MPPP015 Operational Performance of a Bunch by Bunch Digital Damper in the Fermilab Main Injector 1440
  • P. Adamson, P. Adamson
    UCL, London
  • B. Ashmanskas, G.W. Foster, S. U. Hansen, A. Marchionni, D.J. Nicklaus, A. Semenov, D. Wildman
    Fermilab, Batavia, Illinois
  • H. Kang
    Stanford University, Stanford, Califormia
  We have implemented a transverse and longitudinal bunch by bunch digital damper system in the Fermilab Main Injector, using a single digital board for all 3 coordinates. The system has been commissioned over the last year, and is now operational in all MI cycles, damping beam bunched at both 53MHz and 2.5MHz. We describe the performance of this system both for collider operations and high-intensity running for the NuMI project.  
MPPP016 Adaptive Feed Forward Beam Loading Compensation Experience at the Spallation Neutron Source Linac 1467
  • K.-U. Kasemir, M. Champion, M.T. Crofford, H. Ma
    ORNL, Oak Ridge, Tennessee
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

When initial beam studies at the Spallation Neutron Source (SNS) indicated a need for better compensation of the effects of beam loading, a succession of rapid-prototyping and experimentation lead to the development of a simple yet successful adaptive feed forward technique within a few weeks. We describe the process and first results.

MPPP017 User Operation and Upgrades of the Fast Orbit Feedback at the SLS 1538
  • M. Böge, B. Keil, A. Lüdeke, T. Schilcher
    PSI, Villigen
  A report on the performance of the fast orbit feedback (FOFB) in its 2nd year of user operation is given. Photon beam position monitors (XBPM) have been included by means of a slow feedback which changes the reference settings of the FOFB. Users are permitted to change the XBPM references within certain limits while the feedback is running. A fast synchronous readout of the XBPMs allows their integration into the FOFB loop. The FOFB will be extended by an additional beam position monitor (BPM) in order to satisfy the requirements of the upcoming FEMTO project.  
MPPP018 Correction of Insertion Device Induced Orbit Distortions at the SLS 1584
  • M. Böge, J.T.M. Chrin, G. Ingold, B. Keil, J. Krempasky, T. Schilcher, V. Schlott, T. Schmidt, A. Streun
    PSI, Villigen
  Corrections of insertion device (ID) induced orbit distortions at the SLS are performed by means of feed forward schemes down to the micron level at the corresponding photon beam position monitors (XBPMs). The remaining orbit fluctuations are suppressed by XBPM feedbacks which are an integral part of the fast orbit feedback system. As a result, sub-um RMS stability at the XBPMs is achieved while the ID settings are varied.  
MPPP019 Beam Orbit Diagnostics and Control in CANDLE Storage Ring 1655
  • G.A. Amatuni, Y.L. Martirosyan, R.H. Mikaelyan, V.M. Tsakanov, A. Vardanyan
    CANDLE, Yerevan
  Stability requirements for the CANDLE light source are the consequence of a small electron beam size and a tolerable photon beam parameters. In a real machine, the components of the storage ring have static and dynamic imperfections, which cause disturbance of the electron beam and consequently photon beams parameters. In the present paper the basic approaches to the beam diagnostics, control and correction issues for the CANDLE facility are given. The algorithms, electronics and processing hardware are described.