Beam Instrumentation and Feedback

Timing and Longitudinal

Paper Title Page
TUO1A01 Bunched Beam Stochastic Cooling for RHIC 39
 
  • J. M. Brennan, M. Blaskiewicz, F. Severino
    BNL, Upton, Long Island, New York
 
  Stochastic cooling is an effective and well-established accelerator technology for improving beam quality. However, stochastic cooling of high frequency bunched beam has always proved problematic. We have built a stochastic cooling system for heavy ions in RHIC that is used on bunched beam. The purpose is to counteract Intra-Beam Scattering and improve integrated luminosity. The chief technical challenge of bunched beam is the strong coherent frequency components in the beam that contaminate the Schottky spectrum. Technical solutions for overcoming this problem are described. Results from commissioning in one ring of RHIC are reported.  
WEO1A01 Sub-ps Timing and Synchronization Systems for Longitudinal Electron Bunch Profile Measurements 204
 
  • A. Winter
    DESY, Hamburg
 
  Precise timing and synchronization systems have become an increasingly important topic for next generation light sources. Particularly free electron lasers can emit X-ray pulses with pulse durations down to the few-tens of femtoseconds level. In order to utilize this potential temporal resolution for pump-probe experiments, a precise synchronization of the experimental laser to the X-ray pulse and stabilization of the electron beam arrival time at the undulators are mandatory. This requires a timing and synchronization system which can supply ultra-stable phase references over long distances, thus enabling the temporal stabilization of the electron beam to a sub-100 fs level. Furthermore, a precise timing and synchronization system renders possible extremely accurate measurements of the longitudinal electron bunch profile. This talk will give an overview of the status of existing sub-ps timing and synchronization systems and of systems currently under construction.  
WEPB03 Femtosecond Yb-Doped Fiber Laser System at 1 um of Wavelength with 100-nm Bandwidth and Variable Pulse Structure for Accelerator Diagnostics 235
 
  • A. Winter, B. Steffen
    DESY, Hamburg
  • F. O. Ilday
    Bilkent University, Bilkent, Ankara
 
  Laser-based diagnostic systems play an increasingly important role in accelerator diagnostics in, for instance, measurements of the electron bunch length. To date, the laser system of choice for electro-optic experiments has been the Ti:Sa laser. These offer nJ pulse energies at fixed repetition rate between 50-100 MHz, which is not well suited to the bunch structure of facilities such as FLASH (several hundred pulses with 1 MHz spacing at 1-5 Hz repetition rate).The limited robustness, stability and operability of Ti:Sa systems make them less than an ideal candidate for a continuously running measurement system requiring minimal maintenance. Fiber lasers represent a promising alternative, since gating and subsequent amplification is simple and of low cost, hence a pulse pattern corresponding exactly to the linac bunch pattern can be generated. Furthermore, these lasers offer superior robustness at a fraction of the cost of a Ti:Sa laser and have been shown to work without maintenance for several months and longer. Here, we present an ytterbium-doped fiber laser system with 80 nm bandwidth and multi-nJ pulse energy with adjustable bunch pattern for use in electro-optic experiments.  
WEPB05 Streak Camera Measurements of the SOLEIL Bunch Length 241
 
  • M. Labat, L. Cassinari, M.-E. Couprie, R. Nagaoka, D. Pédeau
    SOLEIL, Gif-sur-Yvette
 
  A double sweep streak camera (C5680, Hamamatsu) has been installed on the French third generation light source SOLEIL. The visible radiation of the diagnostics beam-line is used to study the longitudinal profile of the stored electron bunches. We report on the commissioning of the streak camera, as well as on its first uses. Measurements of single-bunch length as a function of various machine parameters such as RF cavity voltage and frequency, and beam current with a few picoseconds resolution are reported, and interpreted in terms of vacuum chamber impedance and beam stability.  
WEPB08 Noise and drift characterization of critical components for the laser based synchronization system at FLASH 250
 
  • B. Lorbeer, B. Lorbeer
    TUHH, Hamburg
  • F. Löhl, F. Ludwig, J. M. Müller, H. Schlarb, A. Winter
    DESY, Hamburg
 
  At FLASH, a new synchronization system based on distributing streams of short laser pulses through optical fibers will be installed and commissioned in 2007. At several end stations, a low drift- and low noise conversion of the optical signal into RF signals is needed. In this paper, we present the influence of photodiodes on the phase stability of the optical pulse streams and investigate the drift performance of the photo-detection scheme for the extraction of the RF signal.  
WEPB12 Measurement of Bunch Lengthening Effects Using a Streak Camera with Reflective Optics 256
 
  • T. Obina, T. Mitsuhashi
    KEK, Ibaraki
 
  For the precise measurement of the bunch length, the incident optics of a streak camera must be free from an optical path difference due to chromatic effects. We designed and installed a reflective optics for the streak camera, and measured the bunch length as a function of the beam current. In the KEK Photon Factory, almost one half of the vacuum components were replaced in 2005. We measured the bunch lengthening effects before and after the replacement. The threshold-current of the microwave instabilities showed the impedance of the storage ring was greatly improved. This paper describes the detail of measurement and the calculations of the impedance of vacuum components.  
WEPB15 A Sub-50 Femtosecond bunch arrival time monitor system for FLASH 262
 
  • F. Löhl, K. E. Hacker, H. Schlarb
    DESY, Hamburg
 
  A bunch arrival time monitor system using the future laser based synchronization system at FLASH has been developed. The signal of a beam pick-up with several GHz bandwidth is sampled by a sub-ps laser pulse using a broadband electro-optical modulator. Bunch arrival time deviations are converted into amplitude modulations of the sampling laser pulses which are then detected by a photo-detector. A resolution of 30 fs could be reached, with the capability towards sub-10 fs level. In this paper we describe the design of the optical system and we present recent results.  
WEPB16 First prototype of an optical cross-correlation based fiber-link stabilization for the FLASH synchronization system 265
 
  • F. Löhl, H. Schlarb
    DESY, Hamburg
  • J. Chen, F. X. Kaertner, J. Kim
    MIT, Cambridge, Massachusetts
 
  A drift free synchronization distribution system with femtosecond accuracy is of great interest for free-electron-lasers such as FLASH or the European XFEL. Stability at that level can be reached by distributing laser pulses from a mode-locked erbium-doped fiber laser master oscillator over actively optical-length stabilized fiber-links. In this paper we present a prototype of a fiber-link stabilization system based on balanced optical cross-correlation. The optical cross-correlation offers drift-free timing jitter detection. With this approach we were able to reduce the timing jitter added by a 400 m long fiber-link installed in a noisy accelerator environment to below 10 fs (rms) over 12 hours.  
WEPB20 Optical System for Measuring Electron Bunch Length and Longitudinal Phase Space at Pitz: Extension and Methodical Investigations 274
 
  • J. W. Bähr, H. L. Luedecke
    DESY Zeuthen, Zeuthen
  • J. Rönsch
    Uni HH, Hamburg
 
  An extended optical system* for the measurement of the electron bunch length and the longitudinal phase space** using a streak camera is installed at PITZ. This system will be extended by two new branches in 2007, one in the straight section behind the booster cavity and another one in the first magnet spectrometer behind the booster cavity. The physics design of the chambers containing the radiators and of the optical system are presented. The results of optical calculations of the whole system will be given. Results of methodical investigations will be shown as well, especially concerning transversal optical resolution and time dispersion.

* J. Baehr et al., DIPAC ‘03, Mainz, Germany 2003** J. Roensch et al. FEL ’05, SLAC, Stanford, USA, 2005

 
WEPB25 Time Domain Measurements at Diamond 289
 
  • C. A. Thomas, G. Rehm
    Diamond, Oxfordshire
 
  We present a set of four complementary measurements of the synchrotron visible light to characterise the stored electron beam at Diamond in the time domain. The electron bunch profiles and its evolution is measured with picosecond accuracy using a dual sweep streak camera. The beam dynamics are also given by a fast photodiode connected to a fast oscilloscope. The fill pattern is measured using a time correlated single photon counting system which has a high dynamic range for bunch purity measurement, and a fast averaging card which gives the fill structure with high accuracy within a short integration time. We describe our set of instruments, discuss their performance and show first results from measurements of Diamond's properties.  
WEPB26 Transition Thermal Processes In Vibrating Wire Monitors 292
 
  • S. G. Arutunian, M. R. Mailian
    YerPhI, Yerevan
  • G. Decker
    ANL, Argonne, Illinois
  • G. Rosenbaum
    UGA, Athens, Georgia
 
  Dynamic characteristics of vibrating wire monitors (VWM) strongly depend on the media where the wire oscillates, and also on the geometry and materials of the wire and VWM housing. On the basis of a one-dimensional model of heat transfer along the wire, the time characteristics of transition processes of thermal equilibrium profiles are defined for wires of different materials and geometry. To decrease the response time of the VWM, a new scheme of measurement with constant mean temperature is suggested. In addition to the flux of particles/radiation deposited on the wire, the additional DC current maintains a constant wire oscillation frequency. The value of DC current serves as measure of particles/radiation flux.  
WEPC02 Developments at Elettra of the Electronics for the Bunch-Arrival Monitor 310
 
  • L. Pavlovič, T. Korošec, M. Vidmar
    Uni LJ, Ljubljana
  • M. Ferianis, F. Rossi
    ELETTRA, Basovizza, Trieste
  • K. E. Hacker, F. Löhl, H. Schlarb
    DESY, Hamburg
 
  Within the framework of the EUROFEL project, a task has been started in 2006 for a joint development of a Bunch Arrival Monitor (BAM), based on the original idea from DESY. ELETTRA is responsible for the development of the VME-controlled clock-delay board of the BAM system. A variable clock-delay circuit (a phase shifter) is required to adjust the acquisition sampling point of the pick-up-modulated optical pulses of the master-laser oscillator. Since the optical pulses have a repetition rate of 40.625MHz (54MHz in the future) and the acquisition sampling frequency is double of this value, the clock-delay module operates in the 80-120MHz frequency range. The clock timing jitter of the acquisition system greatly affects the measurements of the system: the output timing jitter from the clock-delay board should be less than 0.5ps-rms. Therefore, due to the very strict additive timing-jitter requirements, three phase shifter versions were designed, built and phase-noise evaluated. Low-pass-filter implementation achieved 563fs (at 283fs source jitter) of total-system timing jitter, integrated IQ multiplier 365fs (at 188fs of source) and passive IQ modulator 265fs (at 208fs of source).  
WEPC11 FERMI@elettra Timing System: Design and Recent Synchronization Achievements 334
 
  • M. Ferianis
    ELETTRA, Basovizza, Trieste
 
  FERMI@elettra is the fourth generation light source under construction at Sincrotrone Trieste. Being a seeded-FEL source, the requirements for the timing system are very tight as the final goal is a stable seeding process with sub-picosecond electron bunches and seeding laser pulses. Based on demonstrated results achieved in the main laboratories worldwide active in the field, like DESY, LBNL and MIT, an hybrid timing system scheme has been proposed which is currently under development. Both "pulsed" and "continuous wave (CW)" optical timing systems are being deployed, the choice being based on the differences among the different timing system clients; a Low Level Radio Frequency processor is a "quasi-CW" client whereas the lasers and some "longitudinal" diagnostics are "time discrete" clients. In this paper the FERMI@elettra timing system and the recent advances are presented. A pulsed optical clock has been locked to an ultra stable reference; its output pulses distributed over stabilized fiber optic links. As a benchmark client, a femto-second laser oscillator has been synchronized to the optical clock testing different possible schemes.  
WEPC13 Jitter Reduced Pump-Probe Experiments 337
 
  • A. Azima, S. Düsterer, J. Feldhaus, P. Radcliffe, H. Redlin, H. Schlarb
    DESY, Hamburg
  • M. Meyer
    LIXAM, Orsay
 
  For two-colour pump-probe experiments carried out at the free electron laser FLASH@DESY, the FEL laser pulses in the XUV have to be synchronized with femtosecond precision to optical laser pulses (Ti:Sapphire). An electro-optical sampling diagnostic measures the arrival time jitter of the infrared pump-probe laser pulse in respect to the electron bunch of the FEL. Here, the electron arrival time is encoded spatially into the laser pulse profile and readout by an intensified camera. In this paper we report about the improvement of the temporal resolution of pump-probe experiments on gaseous and solid targets using the arrival time data acquired by the described EO-diagnostic.  
WEPC21 Diagnostics of the Waveform of Picosecond Electron Bunches Using the Angular Distribution of Coherent Sub-mmTransition and Diffraction Radiation 355
 
  • A. G. Shkvarunets, R. B. Fiorito
    UMD, College Park, Maryland
  • F. Mueller, V. Schlott
    PSI, Villigen
 
  The spectra of sub-mm wavelength coherent transition radiation (TR) and diffraction radiation (DR) have previously been used to measure the bunch length of picosecond electron beam pulses. However, both the spectral and angular distributions of the radiation from a finite target or aperture with size r, are strong functions of the wavelength, when λ ≈ 2πr/γ where γ is the relativistic factor of the beam. This dependence must be taken into account in the determination of the bunch form factor and bunch shape. Also the spectral density of the bunch is a strong function of wavelength when λ ≈ d, the characteristic length of the bunch. When both the above conditions are fulfilled, i.e. λ ≈ 2πr/γ ≈ d, the spectral and angular distribution (AD) of the radiation are very sensitive to the longitudinal distribution of the bunch. We are investigating the use of the AD of TR or DR, to diagnose the bunch length and shape. Here we present a comparison of measured and calculated angular distributions from two targets: a solid disk and a rectangular slit, which we have used to determine the waveform of the beam bunch produced at PSI’s SLS pre-injector LINAC.  
WEPC22 Synchronization of a 3GHz Repetition Rate Harmonically Mode-Locked Fiber Laser for Optical Timing Applications 358
 
  • L. Banchi, M. Ferianis, F. Rossi
    ELETTRA, Basovizza, Trieste
  • A. Bogoni, P. Ghelfi, L. Poti'
    CNIT, Pisa
 
  We have successfully stabilized a 3GHz Harmonically Mode-Locked fiber ring laser by a PLL feedback control of the cavity length to reduce the pulses RMS timing jitter. The laser cavity is composed of all PM fibers and components to eliminate polarization instabilities and to reduce the vibration sensitivity. The laser stability in terms of timing jitter was around 9ps in the range 10Hz-10MHz. Using a PLL scheme we synchronized the laser repetition rate to an ultra stable RF generator. The noise characteristics of the laser output were measured by observing the SSB noise spectra of the 1st harmonic, from 10Hz to the Nyquist frequency (1.5GHz). We have obtained a global reduction of fiber laser timing jitter value down to less than 100fs in the range 10Hz-10MHz; a complete overlapping between the laser and the RF generator spectral profiles in the loop bandwidth has been observed. An extended investigation has been performed to estimate the phase noise spectra and timing jitter up to 1.5GHz. By doing so, the contribution of the laser supermodes to the phase noise has been taken into account as well, to quantify the true value of the total RMS timing jitter of the optical pulses.  
WEPC28 Timing and Synchronization at the LCLS 373
 
  • P. Krejcik, R. Akre, S. Allison, J. Browne, L. R. Dalesio, J. E. Dusatko, J. C. Frisch, R. Fuller, A. E. Gromme, K. D. Kotturi, S. N. Norum, D. Rogind, W. E. White, S. Zelazny
    SLAC, Menlo Park, California
 
  Timing and synchronization in the LCLS is a three tier process: At level 1 an event generator broadcasts timing fiducials to event receivers over a fiber network. Hardware and software triggers are created in the event receiver according to the digital pattern broadcast at 360 Hz by the event generator. Beam synchronous data acquisition driven by these triggers allows time-stamped acquisition of all diagnostic devices simultaneously on every pulse. Timing fiducials are phase synchronized to the low level RF reference system with 10 ps precision. Level 2 synchronization ensures that individual klystrons powering gun and accelerating sections remain within a few tenths of a degree S-band to the phase reference distribution scheme. The gun laser system is also phase locked to this reference to within 0.5 ps. Level 3 provides synchronization at the 10 fs level between the electron beam and pump-probe laser systems in the end station experiments. This will be achieved with electro-optic sampling of the electron bunch and by synchronizing the laser systems over a stabilized fiber distribution system. A fiber stabilization scheme is currently under test at Lawrence Berkeley Laboratory.