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MO201 Linac Coherent Light Source (LCLS) – Accelerator System Overview linac, damping, simulation, free-electron-laser 7
 
  • P. Krejcik, Z. Huang, J. Wu
    SLAC, Menlo Park, California
  • P. Emma
    SLAC/ARDA, Menlo Park, California
  The Linac Coherent Light Source (LCLS) will be the world's first x-ray free-electron laser (FEL). Pulses of LCLS x-ray FEL will be several orders of magnitude brighter and shorter than most existing sources. These characteristics will enable frontier new science in several areas. To ensure the vitality of FEL lasing, it is critical to preserve the high quality of the electron beam during the acceleration and compression. We will give an overview of the LCLS accelerator system. We will address design essentials and technique challenges to satisfy the FEL requirements. We will report studies on the microbunching instability suppression via a Laser-Heater. The studies clearly prove the necessary of adding the Laser-Heater and show how effectively this Laser-Heater suppresses the instability by enhancing the Landau damping. We will report how to minimize the sensitivity of the final energy spread and the peak current to various system ‘jitters’. To minimize this sensitivity, a feedback system is required together with other diagnostics. With all these considerations, full start-to-end simulations show saturation at 1.5 Å, though the LCLS is expected to be a very challenging machine.  
Transparencies
 
MOP43 The Impact of Longitudinal Drive Beam Jitter on the CLIC Luminosity linac, luminosity, simulation, lattice 138
 
  • D. Schulte, E. J. N. Wilson, F. Zimmermann
    CERN, Geneva
  In the compact linear collider (CLIC) now under study at CERN, the RF power which accelerates the main beam is provided by decelerating a high current drive beam. Errors in the timing and intensity of the drive beam can turn into RF phase and amplitude errors that are coherent along the whole main linac and the resulting error of the final beam energy, in combination with the limited bandwidth of the beam delivery system, can lead to a significant loss of luminosity. We discuss the stability tolerances that must be applied to the drive beam to avoid this loss. We also examine one of the most important sources of this jitter, which stems from the combination of RF jitter in the drive beam accelerator and subsequent bunch compression. Finally we give details of a potential feedback system that can reduce the drive beam jitter.  
 
MOP69 RF Control Modelling Issues for Future Superconducting Accelerators resonance, diagnostics, linac, beam-loading 180
 
  • A. Hofler, J. R. Delayen
    TJNAF, Newport News, Virginia
  • V. Ayvazyan, A. Brandt, S. Simrock
    DESY, Hamburg
  • T. Czarski
    WUT, Warsaw
  • T. Matsumoto
    KEK, Ibaraki
  The development of superconducting accelerators has reached a high level of maturity following the successes of ATLAS at Argonne, CEBAF at Jefferson Lab, the TESLA Test Facility at DESY and many other operational accelerators. As a result many new accelerators under development (e.g. SNS) or proposed (e.g. RIA) will utilize this technology. Covering all aspects from cw to pulsed rf and/or beam, non-relativistic to relativistic particles, medium and high gradients, light to heavy beam loading, linacs, rings, and ERLs, the demands on the rf control system can be quite different for the various accelerators. For the rf control designer it is therefore essential to understand these issues and be able to predict rf system performance based on realistic rf control models. This paper will describe the features that should be included in such models and present an approach which will drive the development of a generic rf system model.  
 
TUP52 Methods for Measuring and Controlling Beam Breakup in High Current ERLs damping, linac, electron, pick-up 387
 
  • C. Tennant, K. Jordan, E. Pozdeyev, R.A. Rimmer, H. Wang
    Jefferson Lab, Newport News, Virginia
  • S. Simrock
    DESY, Hamburg
  It is well known that high current Energy Recovery Linacs (ERL) utilizing superconducting cavities are susceptible to a regenerative type of beam breakup (BBU). The BBU instability is caused by the transverse deflecting higher-order modes (HOMs) of the cavities which can have high impedance. We present MATLab simulation results for the BBU stability using the analysis tools of control theory. In this framework, methods of experimentally determining the threshold current and the means of suppressing the onset of the instability become more transparent. A scheme was developed to determine the threshold current due to a particular HOM by measuring the decay and rise times of the mode's field in response to an amplitude modulated beam as a function of the average electron beam current. To combat the harmful effects of a particularly dangerous mode, two methods of directly damping HOMs through the cavity HOM couplers were demonstrated. In an effort to suppress the BBU in the presence of multiple, dangerous HOMs, a conceptual design for a bunch-by-bunch transverse feedback system has been developed. By implementing beam feedback, the threshold for instability can be increased substantially.  
 
TUP71 Highly Sensitive Measurements of the Dark Current of Superconducting Cavities for TESLA Using a SQUID Based Cryogenic Current Comparator pick-up, electron, shielding, cryogenics 432
 
  • W. Vodel, R. Neubert, S. Nietzsche
    FSU, Jena
  • K. Knaack, M. Wendt, K. Wittenburg
    DESY, Hamburg
  • A. Peters
    GSI, Darmstadt
  This contribution presents a Cryogenic Current Comparator (CCC) as an excellent tool for detecting dark currents generated, e.g. by superconducting cavities for the upcoming TESLA project (X-FEL) at DESY. To achieve the maximum possible energy the gradient of the superconducting RF cavities should be pushed close to the physical limit of 50 MV/m. The undesired field emission of electrons (so-called dark current) of the superconducting RF cavities at strong fields may limit the maximum gradient. The absolute measurement of the dark current in correlation with the gradient will give a proper value to compare and classify the cavities. The main component of the CCC is a highly sensitive LTS-DC SQUID system which is able to measure extremely low magnetic fields, e.g. caused by the dark current. For this reason the input coil of the SQUID is connected across a special designed toroidal niobium pick-up coil for the passing electron beam. A noise limited current resolution of nearly 2 pA/√(Hz) with a measurement bandwidth of up to 70 kHz was achieved in the laboratory. Design issues of the CCC and the application in the CHECHIA cavity test stand at DESY as well as experimental results will be discussed.  
 
TUP73 Beam Instrumentation Using BPM System of the SPring-8 Linac linac, storage-ring, synchrotron, booster 438
 
  • K. Yanagida, T. Asaka, H. Dewa, H. Hanaki, T. Kobayashi, A. Mizuno, S. Suzuki, T.  Taniuchi, H. Tomizawa
    JASRI-SPring-8, Hyogo
  A beam position monitor (BPM) system of the SPring-8 linac has been operated since 2002. The following upgrade programs have been carried out during this period: The BPMs were installed in the linac's dispersive sections. A synchronized accumulation of beam position data into the database system started. A feedback control of steering magnets for beam position stabilization has been under development. In this conference the authors report a performance of the BPM system, and discuss its usefulness for beam diagnostics, machine diagnostics and beam stabilization.  
 
TUP76 Adaptive Feedforward Cancellation of Sinusoidal Disturbances in Superconducting RF Cavities damping, simulation, superconducting-RF, linac 447
 
  • T.H. Kandil, T.L. Grimm, W. Hartung, H. Khalil, J. Popielarski, J. Vincent, R.C. York
    NSCL, East Lansing, Michigan
  A control method, known as adaptive feedforward cancellation (AFC) is applied to damp sinusoidal disturbances due to microphonics in superconducting RF (SRF) cavities. AFC provides a method for damping internal, and external sinusoidal disturbances with known frequencies. It is preferred over other schemes because it uses rudimentary information about the frequency response at the disturbance frequencies, without the necessity of knowing an analytic model (transfer function) of the system. It estimates the magnitude and phase of the sinusoidal disturbance inputs and generates a control signal to cancel their effect. AFC, along with a frequency estimation process, is shown to be very successful in the cancellation of sinusoidal signals from different sources. The results of this research may significantly reduce the power requirements and increase the stability for lightly loaded continuous-wave SRF systems.  
 
TUP77 Status of RF Control System for ISAC II Superconducting Cavities controls, linac, resonance, alignment 450
 
  • K. Fong, S. Fang, M.P. Laverty
    TRIUMF, Vancouver
  The rf control system for ISAC II superconducting cavities is a hybrid analogue/digital system using self-excited feedback loop. It has undergone more than a year of testing and improvements have been made to every aspect of the system, including power up sequencing, phase detection, loop regulation, data acquisition as well as communication with EPICS. With a loaded Q of 100,000, amplitude regulation bandwidth of 20 Hz, phase regulation bandwidth of 5 Hz have been achieved.  
 
TUP78 Diagnostics for the Low Level RF Control for the European XFEL diagnostics, monitoring, laser, radiation 453
 
  • T. Jezynski, P. Pucyk
    WUT, Warsaw
  • S. Simrock
    DESY, Hamburg
  One of the most important aims of the diagnostic system is to provide high reliability. This article describes the concept and the proposal for diagnostic system for Low Level Radio Frequency system for EU-XFEL. It enables immediate location of faults and understanding of their causes, tests the functionality of LLRF system, tests each the electronic board and connections. Diagnostic system tests different system components and compares results from these tests with e.g. from power supplies monitors. Hardware, software and database aspect of diagnostic system is presented. The main part of this paper is devoted to hardware and software specification.  
 
TUP79 A New RF System for the CEBAF Normal Conducting Cavities simulation, linac, electron, extraction 456
 
  • C. Hovater, H. Dong, A. Hofler, G. Lahti, J. Musson, T. Plawski
    TJNAF, Newport News, Virginia
  The CEBAF Accelerator at Jefferson Lab is a 6 GeV five pass electron accelerator consisting of two superconducting linacs joined by independent magnetic transport arcs. CEBAF also has numerous normal conducting cavities for beam conditioning in the injector and for RF extraction to the experimental halls. The RF systems that presently control these cavities are becoming expensive to maintain, therefore a replacement RF control system is now being developed. For the new RF system, cavity field control is maintained digitally using an FPGA which contains the feedback algorithm. The system incorporates digital down conversion, using quadrature under-sampling at an IF frequency of 70 MHz. The VXI bus-crate was chosen as the operating platform because of its excellent RFI/EMI properties and its compatibility with the EPICS control system. The normal conducting cavities operate at both the 1497 MHz accelerating frequency and the sub-harmonic frequency of 499 MHz. To accommodate this, the new design will use different receiver-transmitter daughter cards for each frequency. This paper discuses the development of the new RF system and reports on initial results.  
 
WE103 State of the Art in RF Control linac, diagnostics, resonance, laser 523
 
  • S. Simrock
    DESY, Hamburg
  Nowadays the designer of a new rf control system has access to a wealth of powerful digital, analog, and rf circuitry. The requirements for the rf control system have changed from only controlling the amplitude and phase of the accelerating field to the required degree to stability. Additional tasks include exception handling and extensive build-in diagnostics while pursuing issues related to reliability, operability, and maintainability. Also operation close to the performance limit must be supported while maximizing the availability of the accelerator. With many accelerator projects in planning or under construction several state-of-the art rf control designs have evolved. This paper will present an overview of this new technology and discuss its performance.  
Transparencies
 
THP12 Superconducting RFQs in the PIAVE Injector linac, rfq, cryogenics, target 623
 
  • G. Bisoffi, G. Bassato, G. Bezzon, A. Calore, S. Canella, F. Chiurlotto, A. Lombardi, P. Modanese, A.M. Porcellato, S. Stark
    INFN/LNL, Legnaro, Padova
  The PIAVE superconducting RFQs were installed on the linac line and connected to the TCF50 cryogenic system. First results on the on-line resonator performance (e.g. Q-curves, amplitude and phase locking) are described as well as the behaviour of the fast tuners.  
 
THP23 An Electrode With Molybdenum-Cathode and Titanium-Anode to Minimize Field Emission Dark Currents cathode, electron, ion, vacuum 645
 
  • T. Nakanishi, F. Furuta, T. Gotou, M. Kuwahara, K. Naniwa, S. Okumi, M. Yamamoto, N. Yamamoto, K. Yasui
    DOP Nagoya, Nagoya
  • H. Matsumoto, M. Yoshioka
    KEK, Ibaraki
  • K. Togawa
    RIKEN Spring-8 Harima, Hyogo
  A systematic study to minimize field emission dark currents from high voltage DC electrode has been continued. It is clearly demonstrated that much lower field emissions observed for Molybdenum (Mo) and Titanium (Ti) in comparison to Stainless-steel and Copper. Furthermore, by analyzing gap-length dependence data of the dark current from Mo and Ti, we can find a method to separate the primary field emission currents (FEC) from secondary induced currents (SIC). The latter currents will be created by possible bombardments of metal surface of anode or cathode by electrons or positive ions, respectively. From this data analysis, it is suggested that Mo is suitable for cathode due to its smallest FEC, and Ti is adequate for anode due to relatively small SIC. This prediction was confirmed by our experiment using a pair of Mo and Ti electrode, which showed the total dark current is suppressed below 1 nA at 105 MV/m applied for an area of 7 mm2 with a gap-length of 1.0 mm. Therefore this Mo-Ti electrode seems useful for a high field gradient DC gun, especially for a GaAs-photocathode gun using an NEA (Negative Electron Affinity) surface.  
 
THP35 Development of a Non-Magnetic Inertial Sensor for Vibration Stabilization in a Linear Collider linear-collider, collider, acceleration, damping 681
 
  • J. Frisch, A. Chang, V. Decker, L. Hendrickson, T. Markiewicz, R. Partridge, A. Seryi
    SLAC, Menlo Park, California
  • D. Eric, T. Himel
    SLAC/NLC, Menlo Park, California
  One of the options for controlling vibration of the final focus magnets in a linear collider is to use active feedback based on accelerometers. While commercial geophysics sensors have noise performance that substantially exceeds the requirements for a linear collider, they are physically large, and cannot operate in the strong magnetic field of the detector. Conventional nonmagnetic sensors have excessive noise for this application. We report on the development of a non-magnetic inertial sensor, and on a novel commercial sensor both of which have demonstrated the required noise levels for this application.  
Transparencies
 
THP36 Vibration Stabilization of a Mechanical Model of a X-Band Linear Collider Final Focus Magnet collider, resonance, linear-collider, site 684
 
  • J. Frisch, A. Chang, V. Decker, L. Hendrickson, T. Markiewicz, R. Partridge, A. Seryi
    SLAC, Menlo Park, California
  • E. Eric, L. Eriksson, T. Himel
    SLAC/NLC, Menlo Park, California
  The small beam sizes at the interaction point of a X-band linear collider require mechanical stabilization of the final focus magnets at the nanometer level. While passive systems provide adequate performance at many potential sites, active mechanical stabilization is useful if the natural or cultural ground vibration is higher than expected. A mechanical model of a room temperature linear collider final focus magnet has been constructed and actively stabilized with an accelerometer based system.  
 
THP37 Approaches to Beam Stabilization in X-Band Linear Colliders luminosity, linac, ground-motion, linear-collider 687
 
  • J. Frisch, L. Hendrickson, T. Markiewicz, A. Seryi
    SLAC, Menlo Park, California
  • P. Burrows, S. Molloy, G. White
    Queen Mary University of London, London
  • C. Perry
    OXFORDphysics, Oxford, Oxon
  • T.O. Raubenheimer, T. Thomas
    SLAC/NLC, Menlo Park, California
  In order to stabilize the beams at the interaction point, the X-band linear collider proposes to use a combination of techniques: inter-train and intra-train beam-beam feedback, passive vibration isolation, and active vibration stabilization based on either accelerometers or laser interferometers. These systems operate in a technologically redundant fashion: simulations indicate that if one technique proves unusable in the final machine, the others will still support adequate luminosity. Experiments underway for all of these technologies, have already demonstrated adequate performance.  
 
THP44 The Design and Performance of the Spallation Neutron Source Low-Level RF Control System linac, controls, klystron, coupling 703
 
  • M. Champion, M. Crofford, K. Kasemir, H. Ma, C. Piller
    ORNL/SNS, Oak Ridge, Tennessee
  • L. Doolittle, C. Lionberger, M. Monroy, A. Ratti
    LBNL, Berkeley, California
  • J. Power, H. Shoee
    LANL, Los Alamos, New Mexico
  The Spallation Neutron Source linear accelerator low-level RF control system has been developed within a collaboration of Lawrence Berkeley, Los Alamos, and Oak Ridge national laboratories. Three distinct generations of the system, described in a previous publication [1], have been used to support beam commissioning at Oak Ridge. The third generation system went into production in early 2004, with installation in the coupled-cavity and superconducting linacs to span the remainder of the year. The final design of this system will be presented along with results of performance measurements.

[1] M. Champion, et al, "The Spallation Neutron Source Accelerator Low Level RF Control System", Proceedings of the PAC2003 Conference, Portland, Oregon.

 
 
THP48 A High-Resolution S-band Down-Converting Digital Phase Detector for SASE FEL Use linac, photon, simulation, free-electron-laser 715
 
  • A.E. Grelick, N.D. Arnold
    ANL/APS, Argonne, Illinois
  • J. Carwardine, N. Dimonte, A. Nassiri, T. Smith
    ANL, Argonne, Illinois
  Each of the rf phase detectors in the Advanced Photon Source linac consists of a module that down converts from S-band to 20 MHz followed by an analog I/Q detector. Phase is calculated from one digitized sample per pulse each of I and Q. The resulting data has excellent long-term stability but is noisy enough so that a number of samples must be averaged to get a usable reading. The more recent requirement to support a SASE FEL has presented the need to accurately resolve the relative phase of a single pulse. Replacing analog detection with digital sampling and replacing internal intermediate frequency reference oscillators with a lower noise external oscillator were used to control the two largest components of noise. The implementation of a central, ultralow noise reference oscillator and a distribution system capable of maintaining the low phase noise is described, together with the results obtained to date. The principal remaining technical issue is determining the processing power required as a function of measurement channels per processor, measured pulse repetition rate, intrapulse data bandwidth, and digital filter characteristics. The options and tradeoffs involved and the present status are discussed.  
 
THP52 RF Reference Distribution System for the J-PARC Linac linac, klystron, power-supply, rfq 727
 
  • T. Kobayashi, E. Chishiro
    JAERI, Ibaraki-ken
  • S. Anami, S. Michizono, S. Yamaguchi
    KEK, Ibaraki
  J-PARC (Japan Proton Accelerator Complex) linac, which is 300 m long, consists of 324 MHz accelerating section of the upstream and 972 MHz section (as future plan) of the downstream. In the klystron gallery, totally about 50 RF source control stations will stand for the klystrons and solid-state amplifiers. The error of the accelerating field must be within ±1° in phase and ±1% in amplitude. Thus, the high phase stability is required to the RF reference for all of the low-level RF control systems and the beam monitor systems. This paper presents a final design of the RF reference distribution system for this linac. The RF reference (12 MHz) is distributed to all stations optically. Low-jitter E/O and O/E with temperature stabilizers are developed. The reference is optically amplified and divided into 14 transmission lines, and is delivered through PSOF (the phase-stabilized optical fiber), the temperature of which is stabilized by cooling water. Each of the transmitted signals is divided more into 4 signals by an optical coupler. Our objective for the phase stability of the reference aims at <±0.3° at a 972 MHz frequency.  
 
THP56 Control of the Low Level RF System for J-Parc Linac klystron, linac, proton, vacuum 739
 
  • S. Michizono, S. Anami, E. Kadokura, S. Yamaguchi
    KEK, Ibaraki
  • E. Chishiro, T. Kobayashi, .H. Suzuki
    JAERI, Ibaraki-ken
  A low level RF (LLRF) system for J-Parc linac generates RF and clock signals, drives a klystron, and stabilizes accelerating fields in the cavities. The LLRF system is controlled by two units: a programmable logic controller (PLC) and a compact PCI (cPCI) controller. Functions of the PLC are ON/OFF and UP/DOWN controls, and STATUS and ANALOG monitors. The PLC is locally operated by a touch panel, and remotely operated by an EPICS IOC with Ethernet communication. The cPCI controller is for RF feedback and feed-forward controls, including a cavity tuner control, and then, locally and remotely operated by communication with the PLC. On the other hand, RF waveform data, which are stored in the memory of DSP and CPU boards in the cPCI, are directory transmitted to an EPICS OPI by a request from EPICS.  
 
THP57 Digital Feedback System for J-Parc Linac RF Source linac, simulation, klystron, proton 742
 
  • S. Michizono, S. Anami, S. Yamaguchi
    KEK, Ibaraki
  • T. Kobayashi
    J-PARC, Ibaraki-ken
  At the proton linac of J-Parc (Japan Proton Accelerator Research Complex), an accelerating electric field stability of ±1% in amplitude and ±1° in phase is required for the RF system. In order to accomplish these requirements, a digital feedback system is adopted for flexibility of the feedback (FB) and feed forward (FF) algorism implementation. FPGAs are used for the real-time FB system. A DSP board is also utilized for data processing and communication between FPGAs and a crate control CPU (Host). The system was examined with the DTL cavity and it satisfies the stability specification. In this report, the digital rf system is described and operational stability is also summarized.  
 
THP66 Measurement and Control of Microphonics in High Loaded-Q Superconducting RF Cavities damping, linac, beam-loading, superconductivity 763
 
  • T.L. Grimm, W. Hartung, T.H. Kandil, H. Khalil, J. Popielarski, J. Vincent, R.C. York
    NSCL, East Lansing, Michigan
  • C. Radcliffe
    MSU, East Lansing, Michigan
  Superconducting radio frequency (SRF) linacs with light beam loading, such as the CEBAF upgrade, RIA and energy recovery linacs, operate more efficiently with loaded-Q values >1·107. The narrow band-width puts stringent limits on acceptable levels of vibration, also called microphonics, that detune the SRF cavities. Typical sources of vibration are rotating machinery, fluid fluctuations and ground motion. A prototype RIA 805 MHz v/c=0.47 cryomodule is presently under test in realistic operating conditions [1]. Real-time frequency detuning measurements were made for modulation rates from DC to 1 kHz. At 2 K the maximum frequency deviation was less than 100 Hz peak-to-peak, and was consistent with high loaded-Q operation. The measured modulation spectrum was primarily made up of discrete Fourier components with modulation frequencies less than 80 Hz. Using an accelerometer and helium pressure transducer, the primary sources of vibration were determined to be the high power cryoplant motors and 2 K helium fluctuations. Adaptive feedforward was used to decrease the magnitude of individual Fourier components by four to ten times [2]. Details of the experimental setup and measurements will be presented.

[1] “Experimental Study of an 805 MHz Cryomodule for the Rare Isotope Accelerator”, T.L. Grimm et al., THP70, these proceedings. [2] “Adaptive Feedforward Cancellation (AFC) of Sinusoidal Disturbances in SRF Cavities”, H. Khalil et al., TUP76, these proceedings.

 
Transparencies
 
FR201 Accelerator Control and Global Networks - State of the Art controls, linear-collider, collider, linac 847
 
  • D.P. Gurd
    ORNL, Oak Ridge
  As accelerators increase in size and complexity, demands upon their control systems increase correspondingly. Machine complexity is reflected in complexity of control system hardware and software and careful configuration management is essential. Model-based procedures and fast feedback based upon even faster beam instrumentation are often required. Managing machine protection systems with tens of thousands of inputs is another significant challenge. Increased use of commodity hardware and software introduces new issues of security and control. Large new facilities will increasingly be built by national (e.g. SNS) or international (e.g. a linear collider) collaborations. Building an integrated control system for an accelerator whose development is geographically widespread presents particular problems, not all of them technical. Recent discussions of a “Global Accelerator Network” include the possibility of multiple remote control rooms and no more night shifts. Based upon current experience, observable trends and rampant speculation, this paper looks at the issues and solutions-–-some real, some probable, and some pie-in-the-sky.

*Spallation Neutron Source, ORNL and LANL

 
Transparencies