Paper | Title | Page |
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WEPC01 | Beam Based Measurements of RF Phase and Amplitude Stability at FLASH | 307 |
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Beam based techniques to determine the phase and amplitude stability of the photo-cathode laser, the RF gun and superconducting acceleration modules become key tools for the understanding and quality control for FEL operation critical acceleration sub-system. The measurements are used to identify the sources of instabilities, to determine response functions and to optimize RF feedback parameters and algorithm. In this paper, an overview on the measurement techniques and their limitation is given, together with some important results on the currently achieved RF and laser stability. | ||
WEPC02 | Developments at Elettra of the Electronics for the Bunch-Arrival Monitor | 310 |
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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). | ||
WEPC03 | Secondary Electron Emission Beam Loss Monitor for LHC | 313 |
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Beam Loss Monitoring (BLM) system is a vital part of the active protection of the LHC accelerators elements. It should provide the number of particles lost from the primary hadron beam by measuring the radiation field induced by their interaction with matter surrounding the beam pipe. The LHC BLM system will use ionization chambers as standard detectors but in the areas where very high dose rates are expected, the Secondary Emission Monitor (SEM) chambers will be employed because of their high linearity, low sensitivity and fast response. The SEM needs a high vacuum for proper operation and has to be functional for up to 20 years, therefore all the components were designed according to the UHV requirements and a getter pump was included. The SEM electrodes are made of Ti because of its Secondary Emission Yield (SEY) stability. The sensitivity of the SEM was modeled in Geant4 via the Photo-Absorption Ionization module together with custom parameterization of the very low energy secondary electron production. The prototypes were calibrated by proton beams in CERN PS Booster dump line, SPS transfer line and in PSI Optis line. The results were compared to the simulations. | ||
WEPC04 | Transverse Feedback Development at SOLEIL | 316 |
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The SOLEIL ring is planned to operate in both multibunch and high current per bunch modes. However, the small vertical chamber aperture around the SOLEIL ring enhances the transverse impedance both in its resistive-wall and broadband content, resulting in instabilities that appear at relatively low current compared to the desired values. A decision was therefore taken to install a digital bunch-by-bunch feedback system, with an aim to make it operational from the beginning of the user operation. The system implemented comprises components developed elsewhere, particularly the FPGA processor of Spring-8, chosen among different possible solutions. Using a BPM and a stripline in the diagonal mode, a single unit of the FPGA processor board has shown to successfully suppress resistive-wall and ion induced instabilities in either one or both transverse planes up to 300 mA. The paper discusses the system characteristics including striplines whose shunt impedance was maximised by keeping the coupling impedance small*, the obtained performance as well as future extensions to overcome the encountered limitations.
* C. Mariette ID1209 |
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WEPC06 | Single gain radiation tolerant LHC beam loss acquisition card | 319 |
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The beam loss monitoring system is one of the most critical elements for the protection of the LHC. It must prevent the super conducting magnets from quenches and the machine components from damages, caused by beam losses. Ionization chambers and secondary emission based detectors are used on several locations around the ring. The sensors are producing a signal current, which is related to the losses. This current will be measured by a tunnel card, which acquires, digitizes and transmits the data via an optical link to the surface electronic. The usage of the system, for protection and tuning of the LHC and the scale of the LHC, imposed exceptional specifications of the dynamic range and radiation tolerance. The input dynamic allows measurements between 10pA and 1mA and its protected to high pulse of 1.5kV and its corresponding current. To cover this range, a current to frequency converter in combination with an ADC is used. The integrator output voltage is measured with an ADC to improve the resolution. The radiation tolerance required the adaption of conceptional design and a stringent selection components. | ||
WEPC07 | Injection Diagnostics Using Triggered Bunch-by-Bunch Data Acquisition | 322 |
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Quality of injection is very important for reliable and successful operation of colliders and light sources. In this paper we present a technique for real-time monitoring of injection transients in storage rings. We also demonstrate how the data can be used for tuning the injection system. A novel data processing method, coupled with triggered bunch-by-bunch data acquisition system enables one to monitor the effects of the adjustments nearly in real time. The acquisition and postprocessing technique will be illustrated with the data from PEP-II and DAΦNE. | ||
WEPC08 | Fiberoptics-Based Instrumentation for Storage Ring Beam Diagnostics | 325 |
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We present the results of our experiments at the Advanced Light Source concerning the coupling of synchrotron radiation into optical fibers. Many beam diagnostic devices in today's synchrotron rings make use of the radiation emitted by the circulating particles. Such instruments are placed in close proximity of the accelerator, where in many instances they cannot be easily accessed for safety consideration, or at the end of a beamline, which, because of its cost, can only move the light port a few meters away from the ring. Our method, suitable for all those applications where the longitudinal properties of the beam are measured (i.e. bunch length, phase, etc.), allows placing the diagnostic instruments wherever is more convenient, up to several hundreds of meters away from the tunnel. This would make maintaining and replacing instruments, or switching between them, possible without any access to restricted areas. Additionally, one can use the vast array of optoelectronic devices, developed by the telecommunication industry, for signal analysis. | ||
WEPC09 | Classification of the LHC BLM Ionization Chamber | 328 |
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The LHC beam loss monitoring (BLM) system must prevent the super conducting magnets from quenching and protect the machine components from damage. The main monitor type is an ionization chamber. About 4000 of them will be installed around the ring. The lost beam particles initiate hadronic showers through the magnets and other machine components. These shower particles are measured by the monitors installed on the outside of the accelerator equipment. For the calibration of the BLM system the signal response of the ionization chamber to all relevant particles types and energies (keV to TeV range) is simulated in GEANT4. For validation, the simulations are compared to measurements using protons, neutrons, photons, muons and mixed radiation fields at various energies and intensities. This paper will focus on the signal response of the ionization chamber to various particle types and energies including recombination effects in the chamber gas at high ionization densities. | ||
WEPC10 | Tune, Coupling, and Chromaticity Measurement and Feedback During RHIC Run 7 | 331 |
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Tune feedback was first implemented in RHIC in 2002, as a specialist activity. The transition to full operational status was impeded by dynamic range problems, as well as by overall loop instabilities driven by large coupling. The dynamic range problem was solved by the CERN development of the Direct Diode Detection Analog Front End[1]. Continuous measurement of all projections of the betatron eigenmodes made possible the world's first implementation of coupling feedback during beam acceleration, resolving the problem of overall loop instabilites[2,3]. Simultaneous tune and coupling feedbacks were utilized as specialist activities for ramp development during the 2006 RHIC run. At the beginning of the 2007 RHIC run there remained two obstacles to making these feedbacks fully operational in RHIC - chromaticity measurement and control, and the presence of strong harmonics of the power line frequency in the betatron spectrum. Preliminary investigations of power line harmonics were presented earlier[4]. We report here on progress in tune, coupling, and chromaticity measurement and feedback, and discuss the relevance of our results to the LHC commissioning effort.
[1] M. Gasior and R. Jones, DIPAC 2005, Lyon, p.312.[2] P. Cameron et. al., PRST-AB, Dec 2006. [3] R. Jones et. al., DIPAC 2005, Lyon, p.298.[4] P. Cameron et. al., DIPAC 2005, Lyon, p.33. |
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WEPC11 | FERMI@elettra Timing System: Design and Recent Synchronization Achievements | 334 |
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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 |
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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. | ||
WEPC14 | Segmented Beam Dump for Time Resolved Spectrometry on a High Current Electron Beam | 340 |
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In the CLIC Test Facility 3, the strong coupling between the beam and the accelerating cavities induces transient effects such that the head of the pulse is accelerated twice as much as the rest of the pulse. Three spectrometer lines are installed along the linac with the aim of measuring energy spread versus time with a 20ns resolution. The major difficulty is due to the high power carried by the beam which imposes extreme constraints of thermal and radiation resistances for the detector. This paper presents the design and the performances of a simple and easy-to-maintain device, called segmented dump. In this device, the particles are stopped inside metallic plates and the deposited charge is measured in the same way as in faraday cups. Simulations were carried out with the Monte Carlo code FLUKA in order to evaluate the problems coming from the energy deposition and find ways to prevent or reduce them. The detector resolution has been optimized by choosing the adequate material and thickness for the plates. The overall layout of the monitor is described with a special emphasis on its mechanical assembly. Finally, limitations arising at high beam energies are discussed. | ||
WEPC16 | Excitation Striplines for SOLEIL Fast Transverse Feedback | 343 |
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SOLEIL, the French third generation light source, is equipped with excitation striplines for a tune monitor and for the (bunch-by-bunch) Fast Transverse Feedback* that has been recently implemented. A careful design of the striplines and their vacuum feedthroughs was aimed at maximizing the effectiveness of the excitation power via high shunt impedances, and minimizing the power taken from the beam via low parasitic mode losses. Three stripline kickers have been developed for these applications. We report on their design using RADIA and GdfidL simulation codes, on the fabrication of the striplines, and on the experimental results with beam.
* R. Nagaoka: Transverse Feedback Development at SOLEIL. ID 1257 |
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WEPC17 | Fast Orbit Feeback System Upgrade with New Digital Bpm and Power Supply in the Tls | 346 |
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The BPMs of orbit feedback loop use analogy type in the TLS that is more than 10 years. The analogy type BPM provides high resolution position detection after signal processing. The new generation digital beam position monitor (DBPM) was performed recently. The BPM electronics are commercial available by using direct RF sampling technology, FPGA, and embedded control environment running GNU/Linux. The programmable nature of DBPM system is beneficial for multi-mode high precision beam diagnostics purposes. Sub-micron resolution is achieved for averaged beam position measurement with high update rate. The DBPM are seamless integrated with existed control system and is compatible with old BPM in the orbit feedback loop. In the same time, the corrector power-supply is also upgraded for wide bandwidth control. The integration of old and new BPM, power-supply control for fast orbit feedback will be discussed in this report. | ||
WEPC19 | Toroid Protection System for FLASH | 349 |
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The FLASH fast machine protection includes a beam loss interlock using toroids to measure the beam charge. This system monitors the beam losses across the whole linac while other protection systems are specifically dedicated to critical components. Four protection modes are used to handle different scenarios of losses: charge validation, single bunch, slice and integration modes. This system is based on 4 ADCs to sample the top and bottom of upstream and downstream toroid signals. A microcontroller drives 2 programmable delay generators to adjust the top and bottom ADC trigger during the calibration phase. The samples are then collected by a 200Kgates FPGA to process the various protection modes. At first, a VHDL testbench was developed to generate test vectors at the FPGA design inputs. Then, an electronic testbench simulates the linac signals to validate the global hardware functions. Finally, the toroid protection was tested on FLASH with long bunch train at 1 MHz repetition rate. | ||
WEPC20 | A Real-Time Beam Monitor for Hadrontherapy Applications Based on Thin Foil Secondary Electron Emission and a Back-Thinned Monolithic Pixel Sensor | 352 |
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A novel, non-disruptive beam profile monitor for low intensity light-ion beams has been constructed and tested. The system is designed for use in medical hadrontherapy centers where real-time monitoring of the beam intensity profile is of great importance for optimization of the accelerator operation, patient safety and dose delivery. The beam monitor is based on the detection of secondary electrons emitted from a submicron thick Al2O3/Al foil placed in the beam at an angle of 45 degrees. The present paper reports the latest results achieved with a customized monolithic active pixel array, which provides the beam intensity and position with a precision of better than 1 mm at a 10 kHz frame rate. The sensor chip is back-thinned to achieve the required sensitivity to short-range secondary electrons focused onto the sensor surface. The monitor performance has been tested with a patterned beam, produced with a multi-hole collimator, with the results indicating that the system performs according to its design specifications. | ||
WEPC21 | Diagnostics of the Waveform of Picosecond Electron Bunches Using the Angular Distribution of Coherent Sub-mmTransition and Diffraction Radiation | 355 |
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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 PSIs SLS pre-injector LINAC. | ||
WEPC22 | Synchronization of a 3GHz Repetition Rate Harmonically Mode-Locked Fiber Laser for Optical Timing Applications | 358 |
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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. | ||
WEPC23 | Progress of the Diagnostics at the Proscan Beam Lines | 361 |
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PROSCAN, the dedicated new medical facility at PSI using proton beams for the treatment of deep seated tumours and eye melanoma, has entered the operational phase. Air and N2 filled ionisation chambers and secondary emission monitors in several configurations are used as current monitors, profile monitors, halo, position and loss monitors at the PROSCAN beam lines. The operation experience and improvements of these diagnostics as well as of the multi-leaf- and the standard faraday-cups and of the profile-evaluation technique are reported. Additional variants of ionisation chamber position monitors adapted to local requirements are now under construction. Criteria for interlocks which control beam parameters and the correct operation of diagnostics are discussed as well as dedicated procedures for checking the function of the built-in diagnostics. The fast exchange of beam-line components and spare parts are briefly mentioned. | ||
WEPC24 | A Self Calibrating Real Time Multi-Channel Profile Monitor for the Isis Proton Synchrotron | 364 |
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A (+ion) gas ionisation profile monitor (GIPM) has been developed at the Rutherford Appleton Laboratory to capture 'real time' beam profile data within the accelerating ring of the 800MeV ISIS proton sychrotron. The GIPM uses an array of 40 Channeltron detectors, operating at a gain of ~104, to measure the transverse beam profile in the horizontal plane. The data obtained is an average of two rotations of the beam bunch, a limitation due soley to the speed of the +ions. Fast electronics and a multi-channel PXI / LabView data acquisition system are used to simultaneously process and display the 40 channels of beam profile information. Variations in the Channeltrons gain are dealt with using an independent motor driven +ion detector. The beam profiles obtained from this single detector are stored and used as a calibration file to correct data from the new multi-channel profile monitor. | ||
WEPC26 | Transverse Bunch-by-Bunch Feedback for the VEPP-4M Electron-Positron Collider | 367 |
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Transverse mode coupling instability (TMCI or fast head-tail) is the principal beam current limitation of the VEPP-4M electron-positron collider. For the high-energy physics experiments at the 5.5 GeV energy, the VEPP-4M bunch current should exceed much the TMCI threshold. To suppress transverse beam instabilities, a broadband bunch-by-bunch digital feedback system is developed. The feedback concept is described, the system layout and first beam measurements are presented. | ||
WEPC27 | Segmented Foil SEM Grids for High-Intensity Proton Beams at Fermilab | 370 |
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The extracted beam transport lines and transfer lines between accelerators at Fermilab must operate at ever higher proton fluences to service the neutrino program and the production of antiprotons for the Tevatron collider program. The high proton fluences place stringent criteria on invasive instrumentation to measure proton beam profiles. Based on a design from CERN, we have built SEM's consisting of Ti foils segmented at either 1.0mm or 0.5mm pitch. The foils are 5um thick Titanium, and two planes of the segmented foils per SEM chamber provides both horizontal and vertical beam profiles. The foil SEM's provide several features over the Au-plated 75 um Ø W-wire SEM's previously in use at Fermilab: (1) a factor 50-60 lower fractional beam loss; (2) greater longevity of Ti signal yield, as compared with W or Au-W; (3) a 'bayonnette'-style frame permitting insertion/retraction from the beam without interruption of operations; and (4) reduced calculated beam-heating from the high-intensity proton-pulses, which results in less sag of the wires/foils. Experience with these detectors after two years' operations in 8 and 120GeV beams will be summarized. | ||
WEPC28 | Timing and Synchronization at the LCLS | 373 |
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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. |