| Paper | Title | Page |
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| WEPB01 | Design of an Electron Beam Energy Control Loop Using Transverse Dispersion | 229 |
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| Stability in mean electron beam energy is of highest interest for a number of experiments performed at the ELBE accelerator. Energy drifts affect parameters of the generated Bremsstrahlung spectra, X-rays or infrared light, as well as the beam trajectory at the production targets or through the FEL waveguide, respectively. In practise, we observe a slow drifting of the effective accelerating field during the first hours after a machine power-up or after switching to different nominal beam energies. Initially, this effect was compensated manually. A first order automation solution has been developed that corrects the resulting energy drift continuously, using a non-intrusive beam position monitor placed in a transversely dispersive part of the beam guide. This paper describes the beam line setup and the simplified dynamic model of the control loop derived from it. Calculation of controller parameters using standard a standard method is shown. The user interface of the control system and working conditions for the loop are explained. Operational performance and conclusions towards improvements close this contribution. | ||
| WEPB02 | Design of an Intra-Bunch-Train Feedback System for the European X-Ray FEL | 232 |
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| After joining the preparatory phase of the European X-ray FEL project, the Paul Scherrer Institute 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 FLASH linac of the collaboration partner DESY. The proposed IBFB topology consists of two beam position monitors ("upstream BPMs") followed by two kicker magnets for each transverse plane and two more BPMs ("downstream BPMs"). By measuring the position of each bunch at the upstream BPMs and applying suitable transverse kicks individually to the following bunches, the architecture of the FPGA-based digital IBFB electronics (with a latency preferably below the bunch spacing of 200 ns and 1000 ns for the XFEL and FLASH) allows to damp beam motions up to hundreds of kHz. In addition to the FPGA-based feedback, DSPs enable adaptive feed-forward correction of repetitive beam motions as well as feedback parameter optimisation using the downstream BPMs. This paper gives an overview of the architecture and status of the IBFB subsystems being developed, like stripline BPMs, digital electronics and kicker magnets. | ||
| WEPB03 | Femtosecond Yb-Doped Fiber Laser System at 1 um of Wavelength with 100-nm Bandwidth and Variable Pulse Structure for Accelerator Diagnostics | 235 |
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| 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. | ||
| WEPB04 | The VEPP-4M Dynamic Aperture Determination Through the Precise Measurement of the Beam Lifetime | 238 |
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| To determine experimentally the particle stable area in the electron-positron collider VEPP-4M we measure the beam life time with high accuracy as a function of moving aperture. The measurement is performed by a photodiode installed in the collider diagnostic beam line. The experimental set up and the measurement results are described. Comparison with the tracking simulation is presented. | ||
| WEPB05 | Streak Camera Measurements of the SOLEIL Bunch Length | 241 |
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| 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. | ||
| WEPB06 | Direct Comparison of the Methods of Beam Energy Spread Determination in the VEPP-4M Collider | 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.
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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| WEPB07 | Time Domain Diagnostics for the ISAC-II Superconducting Heavy Ion Linac | 247 |
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| The medium beta section of the ISAC-II superconducting linac has 20 bulk niobium quarter wave resonators and adds up to 20 MV of energy to the 1.5Mev/u and A/q<=6 ion beam injected from the ISAC-I accelerators. The commissioning of this new linac started April 2006 and the first radioactive beam was delivered to an experiment in January 2007. A standard array of ISAC diagnostics were added to the ISAC-II section to commission and tune the transport beamline and linac optics. In addition two new devices were developed: an ion implanted silicon detector measuring beam particles scattered from a gold foil and time of flight (TOF) monitors based on micro-channel plates. These are used both to tune the LINAC and to characterize the accelerated beams in the longitudinal phase space. The TOF monitors have the time resolution below 100ps, energy resolution of 0.1% and dynamic range spanning 6 orders of magnitude. Data acquisition and analysis is highly automatic and integrated into the EPICS based ISAC control system. Design of the monitors and first measurements will be presented. | ||
| WEPB08 | Noise and drift characterization of critical components for the laser based synchronization system at FLASH | 250 |
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| 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. | ||
| WEPB09 | Mechanical Design of the Intensity Measurement Devices for the LHC | 253 |
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| The intensity measurement for the LHC ring is provided by eight current transformers: 2 DC current transformers (DCCTs) and 2 fast transformers (FBCTs) per vacuum chamber. The measurement precision of 1uArms at averaging over 1s time interval for the DCCTs and ±109 charges in 25ns bunch measurements for the FBCTs is required. Such constraints call for low noise electronics and a compact magnetically shielded mechanical design. Due to ultra high vacuum requirements in the LHC the vacuum chambers are equipped with the non-evaporable getter (NEG) film. The NEG is activated by heating the vacuum chamber to 200°C and more. Such temperatures affect the structure of the magnetic materials, which form the base part of the intensity measurement devices, and degrade their performance. A cooling circuit is needed. Due to the mechanical constraints, the cooling circuit, as well as heating element must form an integral part of the design. The paper presents the solution of these problems and discusses the mechanical construction of the DCCTs and FBCTs currently being installed in the LHC. | ||
| WEPB12 | Measurement of Bunch Lengthening Effects Using a Streak Camera with Reflective Optics | 256 |
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| 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. | ||
| WEPB13 | Focusing of Optical Transition and Diffraction Radiation by a Spherical Target | 259 |
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During the last few years Transition Radiation (TR) and Diffraction Radiation (DR) have been intensively studied for different applications such as diagnostics of electron beam size, emittance, length, energy spread, etc. For extremely high-energy electrons the broadening of TR (DR) spatial distribution due to “pre-wave” zone effect [*] leads to distortion of the radiation characteristics and decreasing of photon concentration per unit square detector. In papers [**,***] it was shown that using a spherical target one can make TR (DR) distribution in the pre-wave zone identical to a far-field one. To verify our approach we carried out an experiment at KEK-ATF extraction line with electron beam energy of 1.28 GeV using a spherical target to focus optical TR (DR) at the distance of L=440 mm which corresponds to an extreme pre-wave zone. We also measured OTR (ODR) characteristics from a flat target in order to compare them with OTR (ODR) characteristics from the spherical one. We clearly observed that OTR (ODR) angular distribution from the spherical target is narrower than from a flat one and it’s very similar to a far-field zone distribution as it was predicted by the theory.
* V. A.Verzilov, PLA 273(2000)135** P. V.Karataev, PLA 345(2005)428*** A. P. Potylitsyn and R. O. Rezaev, NIMB 252(2006)44 |
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| WEPB15 | A Sub-50 Femtosecond bunch arrival time monitor system for FLASH | 262 |
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| 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 |
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| 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. | ||
| WEPB18 | Electron Beam Temperature Measurements at the Fermilab Medium Energy Electron Cooler | 268 |
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| The Fermilab Recycler ring employs an electron cooler to store and cool 8.9-GeV antiprotons. The cooler is based on an electrostatic accelerator (Pelletron) working in an energy-recovery regime. Several techniques for determining the characteristics of the beam dynamics have been investigated. Beam temperature measurements using OTR in conjunction with a Pepper-pot have been made at several settings of the upstream optics of the machine. Without temperature the pepper-pot hole images would have sharp boundaries. A finite temperature makes these boundaries broader. Thus, comparison of the ratios of the hole image boundaries and intensities is a measure of the beam temperature. In this paper we report the results so far obtained using this technique. | ||
| WEPB19 | Digital Analysis of Beam Diagnostic Noise | 271 |
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| Results will be presented of recently developed, VME-based electronic modules, a digital beam position monitor (dBPM) and a logarithmic current measurement electronics (VME-LogIV). The dBPM is based on digital receiver technology and processes the signals from 4 pick-up coils. Features of the dBPM are the direct frequency down-converting of the RF 2nd harmonic 101.26MHz) signals (no analogue LO), the remote control of the front end amplifier and the online measurement of individual channel overall gain using 101.31 MHz pilot signals. Various data rates for position measurements at up to 10 kHz are possible. The VME-LogIV can simultaneously measure up to 32 channels at an effective sampling frequency of 5 kHz for the multiple wire profile monitors, also called harps. Fluctuations up to a few kHz of the beam intensity and beam position can thus be analyzed in detail with both of these new systems. Fluctuations from different dBPMs can be compared using coherence spectra measurement. The origin of the VME-LogIV noise can be analyzed using power and coherence spectra, and compared to the noise of the ion source. The results of this analysis will be discussed. | ||
| WEPB20 | Optical System for Measuring Electron Bunch Length and Longitudinal Phase Space at Pitz: Extension and Methodical Investigations | 274 |
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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 |
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| WEPB21 | Kicker Based Tune Measurement for DELTA | 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. | ||
| WEPB22 | Touschek Lifetime Measurement with a Spurious Bunch in UVSOR-II Electron Storage Ring | 280 |
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We have developed a method to measure the Touschek beam lifetime of an electron storage ring using spurious bunches in single-bunch operation by measuring change in the single-bunch impurity over time. To measure a spurious bunch and the main bunch simultaneously, we use a photon counting method with sufficient dynamic range and response time. We demonstrated the method by measuring the Touschek beam lifetime in the UVSOR-II electron storage ring. We find that the Touschek beam lifetime dominates the total beam lifetime in UVSOR-II in usual vacuum condition. The Touschek beam lifetime measurement in multibunch operation with the method will be discussed in the presentation.
A. Mochihashi, M. Katoh, M. Hosaka, Y. Takashima, Y. Hori, NIM-A 572 (2007) 1033-1041. |
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| WEPB23 | Beam Diagnostics Development for the Cryogenic Storage Ring CSR | 283 |
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| A cryogenic storage ring is under construction at the MPI-K Heidelberg. It consists of electrostatic elements and has a circumference of ~35m. The CSR shall be used for storage of rotationally non-excited molecules and highly charged ions, therefore extremely low temperatures (<4K) and gas pressures (10-15 mbar) are required. The ring shall also be operational at room temperature and bakeable to at least 300°C. The maximum energy of singly charged ions is 300keV, intensities will be in the range 1nA – 1uA. For the mass range, A<100 is taken as reasonable design value, in later stages of CSR operation experiments with heavier ions are foreseen. Due to the exceptional boundary conditions we are working on new or further developments for most of the diagnostics devices. For example our RGMs have to produce their own local pressure bumps. The MCPs have to work at temperatures around 4K. The beam position pickups shall be operated in resonant mode for increased sensitivity. Our beam profiler will use secondary electrons from a stopper plate, which allows beam imaging in the intensity range 102 to 1012 pps. For intensity measurements a SQUID CCC system is under discussion. | ||
| WEPB24 | Machine Protection and Interlock Systems at Synchrotron SOLEIL | 286 |
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| SOLEIL is a third generation Synchrotron radiation source located in France near Paris, having the classical accelerator structure consisting of a Linac pre-accelerator, a Booster accelerator and a Storage Ring, which are connected by two transfer lines[1]. Since January, the Storage Ring delivers photon beam to 9 beamlines. In order to protect the very sensitive and essential equipment during machine operation, (vacuum chambers, vacuum valves, mirrors, etc.) an interlock system has been implemented. This system is based on industrial and autonomous PLC (Programmable Logic Controller). This paper describes each level of the interlock chain from the diagnostics and vacuum sensors and processes, up to the backbone of the interlock system which stops the RF system. | ||
| WEPB25 | Time Domain Measurements at Diamond | 289 |
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| 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 |
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| 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. | ||
| WEPB28 | First Tests of the Transverse Multibunch Feedback at Diamond | 295 |
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| This paper describes the design and initial tests of the transverse multibunch feedback system under development at Diamond. The system is designed to damp instabilities up to 250MHz in both the vertical and horizontal plane. This will lead to an increase of instability thresholds which will permit a reduction of chromaticity and thus should improve dynamic aperture and life time. | ||
| WEPB29 | Bunch-by-Bunch Longitudinal Diagnostics at DAΦNE by IR Light | 298 |
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| Compact uncooled HgCdTe semiconductor detectors optimized in the mid-IR range have been used to record time resolved single bunch synchrotron radiation (SR) emissions from the DAΦNE e- main ring. These devices allow a low cost bunch-by-bunch longitudinal diagnostics. Indeed, the detectors make possible to record a train of 2.7 ns long bunches per turn. A comparison with synchrotron light signals coming from the e+ ring is stimulating but at DAΦNE only two SR beamlines are operational and because of the lack of apertures in the main wall no easy alternatives exist for the e+ ring. To solve the problem, a compact SR port has been considered and is going to be implemented on the positron ring. A small dedicated vacuum chamber with a ZnSe infrared window and remote controlled mirrors will be installed to focus the light on the IR detectors. The source characteristics have been simulated and the optical system with the complete acquisition system will be described. When ready, the real time comparison between data collected on the two beams will be performed improving accelerator diagnostics and as a major tool to increase the stored currents in the e+ ring and the collider luminosity. | ||
| WEPB30 | Current Status of the SQUID Based Cryogenic Current Comparator for Absolute Measurements of the Dark Current of Superconducting RF Accelerator Cavities | 301 |
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| This contribution gives an overview on the current status of a LTS-SQUID based Cryogenic Current Comparator (CCC) for detecting dark currents, generated for example by superconducting cavities for the upcoming X-FEL project. To achieve the maximum possible energy the gradients of the superconducting RF accelerator cavities should be pushed close to the physical limit of 50 MV/m. The so-called dark current of the superconducting RF cavities at strong electric fields may limit the maximum gradient. The absolute measurement of the dark current in correlation with the gradient will give a proper value classify the cavities. The main component of the CCC is a LTS-DC SQUID system which allows us to measure extremely low magnetic fields, caused by extracted dark currents of RF cavities under test. For this reason the SQUID input coil is connected across a toroidal superconducting pick-up coil (inner diameter: about 100 mm) for the passing electron beam. A noise limited current resolution of 40 pA/sqrt(Hz) with a measurement bandwidth of up to 70 kHz was achieved. Design issues and the application for the CHECHIA cavity test stand at DESY as well as experimental results will be discussed. | ||
| WEPB31 | Injector Diagnostics Overview of SPIRAL2 Accelerator | 304 |
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| The SPIRAL2 project is based on a multi-beam driver in order to allow both ISOL and low-energy in-flight techniques to produce Radioactive Ion beams (RIB). A superconducting light/heavy-ion linac capable of accelerating 5 mA deuterons up to 40 MeV and 1 mA ions up to 14.5 MeV/u is used to bombard both thick and thin targets. These beams could be used for the production of intense RIB by several reaction mechanisms (fusion, fission, transfer, etc.). The post acceleration of RIB in the SPIRAL2 project is assured by the existing CIME cyclotron. SPIRAL2 beams, both before and after acceleration, can be used in the present experimental area of GANIL. The construction phase of SPIRAL2 is being started since the 1st of July 2005. An injector design overview is presented with diagnostics used to tune and qualify beams. |