CLASSE, Ithaca, New York
A need for femtosecond resolution beam arrival time measurements has arisen with the transition from many-picosecond-long bunches in ring-based accelerators to a few femtosecond-long bunches in high- gain free-electron lasers. Here we present an electro-optical detection scheme that uses the signal of a beam pick-up to modulate the intensity of a femtosecond laser pulse train. By detecting the energies of the laser pulses, the bunch arrival time can be deduced. We tested this scheme by distributing a laser pulse train to two locations in the FLASH linac, separated by 60 m, using length-stabilized optical fibers. By measuring the arrival times of the same electron bunches at these two locations, we determined an rms bunch arrival time resolution of 6 fs. This unprecedented monitor resolution allowed us to reduce the beam arrival time jitter from almost 200 fs down to 25 fs with an intra-bunch train feedback. Alternatively, the same detection scheme can be used for large dynamic range micrometer-resolution beam position measurements by using a stripline-type pickup mounted perpendicularly to the beam path, and then detecting the arrival time difference of both pick-up signals.
DESY, Hamburg
By using magnetic chicane bunch compressors, high-gain free-electron lasers are capable of generating femtosecond electron bunches with peak currents in the kilo-ampere range. For accurate control of the longitudinal dynamics during this compression process, high-precision beam energy and arrival-time monitors are required. Here we present an electro-optical detection scheme that uses the signal of a beam pickup to modulate the intensity of a femtosecond laser pulse train. By detecting the energies of the laser pulses, the arrival-time of the pickup signal can be deduced. Depending on the choice of the beam pickup, this technique allows for high-resolution beam position measurements inside of magnetic chicanes and/or for femtosecond-resolution bunch arrival-time measurements. In first prototypes we realized a beam position monitor with a resolution of 3 μm (rms) over a many-centimeter dynamic range and a bunch arrival-time monitor with a resolution of 6 fs (rms) relative to a pulsed optical reference signal.
CERN, Geneva
This presentation will detail the performance achieved to date with all the main LHC beam instrumentation systems. It will include an overview of the beam loss system and its role in machine protection, along with that of the beam position system and its use for automatic orbit control. Results will be shown from the highly sensitive base band tune system as well as the bunch-by-bunch and DC beam current transformer systems, the synchrotron light monitoring systems, the wire scanner system and OTR screens. It will also cover the US-LARP contribution to the LHC in the form of results from the collision rate monitors developed by LBL and the Schottky monitors developed by FNAL.
Diamond, Oxfordshire
With refined lattice tuning it becomes increasingly important to monitor or feedback on many parameters to keep stable optimum operating conditions. To this end we present techniques to measure betatron tune, chromaticity, betafunction magnitude/phase, and orbit response matrices all in such a way that no disturbance to the stored beam can be observed by the users of the light source. Examples of measurements for the various categories are compared to established methods, and their use in feedback schemes is discussed.
ANL, Argonne
Recent developments at the Advanced Photon Source (APS) in high-resolution beam position monitoring for both the electron and the x-ray beams has provided an opportunity to study beam motion well below the measurement threshold of the standard suite of instrumentation used for orbit control. The APS diagnostics undulator beamline 35-ID has been configured to use a large variety of high-resolution beam position monitor (BPM) technologies. The source-point electron rf BPMs use commercially available Libera Brilliance electronics from Instrumentation Technologies, together with in-house-developed field-programmable gate array-based data acquisition digitizing broadband (10 MHz) amplitude-to-phase monopulse receivers. Photo-emission-based photon BPMs are deployed in the 35-ID front end at distances of 16 and 20 meters from the source, and a prototype x-ray fluorescence-based photon BPM is located at the end of the beamline, approximately 42 meters from the source. Detailed results describing AC noise and long-term drift performance studies will be provided.
LANL, Los Alamos, New Mexico
This study evaluates a technique for the closed-loop position and velocity control of a wire scanner actuator. The focus of this technique is to drive a stepper motor-driven actuator through a 1-mm move using a combination of velocity feedback control and position feedback control. More specifically, the velocity feedback control will be utilized to provide a smooth motion as the controller drives the actuator through a pre-planned motion profile. Once the controller has positioned the actuator within a certain distance of the target position, the controller will transition to position-based feedback control, bringing the actuator to its target position and completing the move. Position and velocity data is presented detailing how the actuator performed relative to its commanded movement. Finally, the layout of, and algorithms employed by the wire scanner control system are presented.
I-Tech, Solkan
SOLEIL, Gif-sur-Yvette
Libera Photon is the new Photon Beam Position Processor (PBPM) from the Instrumentation Technologies. First measurements on real beam have been done at SOLEIL Synchrotron. The module was connected to a PBPM installed on the DIFFABS bending magnet beam line. Three different beam position experiments were done: measurement of position at beam bump (± 500 μm), beam current dependence and filling pattern dependence. Measurements were done with internal BIAS voltage source set to -70 V. Measured current was in the range up to 250 μA on the sensor. Measurements were done on standard 100 kS/s, 10 kS/s and 10 S/s data flows with different bandwidths. The article discusses the results and consequential improvements of the device.
SLAC, Menlo Park, California
SSRL designed and built beam position electronics for its SPEAR3 storage ring. We designed the electronics, using digital receiver technology, for highly accurate turn by turn measurements of both the position and arrival time of the beam, allowing us to use this system to measure the betatron and synchrotron tunes of the beam. The dynamic range of the system allows us to measure the properties of the beam at currents ranging from those of single bunch injection to those of the full SPEAR stored beam. This paper discusses the architecture of the electronics, presents their performance specifications, and shows a range of applications of this system for accelerator physics experiments.
BNL, Upton, Long Island, New York
An internal R&D program has been undertaken at BNL to develop an RF BPM to meet all requirements of both the injection system and storage ring. The RF BPM architecture consists of an Analog Front-End (AFE) board and a Digital Front-End board (DFE) contained in a 1U 19" chassis. An external passive RF signal processor has been developed that will be located near the RF BPM pickups. The partitioning into two boards enables a flexible Software Defined Instrument. A model-based design flow has been adopted utilizing AWR VSS, Simulink, and Xilinx System Generator for algorithm development and AFE impairment performance analysis. The DFE architecture consists of a Virtex-6 with MicroBlaze embedded processor. An optional Intel Atom SBC is also supported. The AFE is based on a bandpass sampling architecture utilizing 16-bit ADCs. Long-term drift is corrected by inclusion of an out-of-band calibration tone. An RF BPM Calibration Tool is being developed for removal of systematic errors and performance verification. In this contribution we will present a detailed overview of the architecture, compare simulation results to laboratory performance, and report beam test results.
CERN, Geneva
The fast beam current transformers (FBCTs) for the Large Hadron Collider (LHC) were designed to provide bunch to bunch and turn by turn intensity measurements. The required bunch to bunch measurements together with a large machine circumference call for stringent control of the transmission bandwidth, droop and DC offsets in the front-end electronics. In addition, two measurement dynamic ranges are needed to achieve the required measurement precision, increasing the complexity of the calibration. This paper reports on the analysis of the measurement and calibration methods, discusses theoretical precision limits and system limitations and provides a comparison of the theoretical results with the real data measured during the LHC start-up.
CERN, Geneva
The BBQ tune (Q) and chromaticity (Q') diagnostic systems played a crucial role during LHC commissioning, both in establishing circulating beam and for the first ramps. Early on, they allowed identification of issues such as the residual tune stability, beam spectrum interferences and beam-beam effects – all of which may impact beam life times and are therefore being addressed in view of nominal LHC operation. This contribution discusses the initial beam stability in relation to the achieved instrumentation sensitivity, corresponding tune frequency and chromaticity resolution.
BNL, Upton, Long Island, New York
Throughout RHIC Run-9 (polarized protons) and Run-10 (gold), numerous modifications to the Baseband Tune (BBQ) system were made. Hardware and software improvements resulted in improved resolution and control, allowing the system to overcome challenges from competing 60 Hz mains harmonics, other spectral content, and other beam issues. Test points from the Analog Front End (AFE) were added and connected to diagnostics that allow us to view signals, such as frequency spectra on a Sr785 dynamic signal analyzer, in real time. Also, additional data can now be logged using a National Instruments DAQ. Development time using tune feedback to obtain full-energy beams at RHIC has been significantly reduced from many ramps over a few weeks, to just a few ramps over several hours. For many years BBQ was an expert-only system, but the many improvements allowed BBQ to finally be handed over to the Operations Staff for routine control.
BNL, Upton, Long Island, New York
AC-dipole magnets are typically implemented as a parallel LC resonant circuit. To maximize efficiency, it’s beneficial to operate at a high Q. This, however, limits the magnet to a narrow frequency range. Current designs therefore deliberately spoil the Q to provide a wider bandwidth at the cost of efficiency. Dynamically tuning the resonant circuit tries to maintain a high efficiency while providing a wide frequency range. The results of ongoing efforts at BNL to implement dynamically tuned high-Q AC dipoles will be presented.
SLAC, Menlo Park, California
Measurement of time-of-arrival or instantaneous longitudinal position is a fundamental beam diagnostic. We present results from a stripline transversal periodic coupler structure which forms the heart of a sub-ps beam timing detector. This filter structure approximates a sinx/x response in the frequency domain which corresponds to a limited pulse length response in the time domain. These techniques have been used extensively in beam feedback systems at 3 GHz center frequencies with operational single-shot resolutions of 200 fs[1]. We present a new design, based on a 11.424 GHz center frequency, which is intended to offer a factor of four improvement in time resolution. Two-dimensional electromagnetic simulation results are shown, and the design optimization approach leading to the final circuit implementation is illustrated. The prototype circuit has been fabricated on 60mil Rogers 4003 and lab frequency domain and time domain data are compared to the 2-D simulation results. Performance of the prototype circuit is shown with applicability to sub-ps beam measurements in LINAC and FEL applications.
NSRRC, Hsinchu
Taiwan Photon Source (TPS) is a 3 GeV synchrotron light source which being in construction at NSRRC. Designs of various diagnostics are undergoing and will deploy in future to satisfy stringent requirements of TPS for commissioning, operation, and top-off injection. Design of the diagnostics for beam intensity observation, trajectory and beam positions measurement, destructive profile measurement, synchrotron radiation monitors, beam loss monitors, orbit and bunch-by-bunch feedbacks, filling pattern, etc. are in final design phase. Details of current status and implementation of the planned beam instrumentation system for the TPS will summary in this report.
NSRRC, Hsinchu
Diagnostics of the 1.5 GeV Taiwan Light Source (TLS) has been continue upgraded since it operation started in 1993. BPM electronics and orbit feedback system have been upgrade in 2008. Commercial photon BPM electronics was tested recently. The bunch-by-bunch feedback have been deployed to improve beam stability. These upgrades are contributed to improve beam quality a lots. These efforts will be addressed also.
BNL, Upton, Long Island, New York
Slow variations of the RHIC closed orbit have been strongly influenced by diurnal variations. These variations affect the reproducibility of RHIC operation and might have contributed to proton beam polarization degradation during past polarized proton runs. We have developed and commissioned a slow orbit feedback system in RHIC Run-10 to diminish these variations and improve energy ramp commissioning and tuning efficiency. This orbit feedback uses multiple dipole correctors and orbit data from an existing beam position monitor system. The precision of the orbit feedback system has resulted directly from application of an improved algorithm for measurement of the average orbit, from improved survey offsets and various measures taken to ensure deterministic delivery of the BPM data. Closed orbit corrections are calculated with an online model-based SVD algorithm, and applied by a control loop operating at up to 1 Hz rate. We report on the feedback design and implementation, and commissioning and operational experience in RHIC Run-10.
BNL, Upton, Long Island, New York
A diffraction-limited storage ring like NSLS2 sets more stringent beam stability requirements. Due to resistive wall impedance and fast-ion effect, transverse instabilities will happen at low current (~15 mA). An active transverse feedback system has been designed to cure the betatron oscillations. The system will have a <200 us damping rate at 50 0mA to suppress the fast-ion instability, which is severe in the vertical plane due to small beam size.
LBNL, Berkeley, California
A hardware system that acquires and stores a large buffer of bunch-by-bunch 16-bit data has been realized. A high resolution (up to 16-bit) analog-to-digital converter (ADC), or bank of ADCs, samples the analog signal at the bunch frequency. The digitized data is fed into a Field Programmable Gate Array (FPGA), which contains an interface to a bank of double data rate (DDR) SDRAM type memory. With appropriate data bus widths, the FPGA bursts the ADC data into the DDR SDRAM fast enough to keep up with the bunch-by-bunch ADC data continuously. The realized system demonstrates continuous data transfer at a rate of 1 GByte/sec, or 16-bit data at 500 MHz, into a 64MByte SDRAM. This paper discusses the implementation of this system and the future of this architecture for bunch-by-bunch diagnostics.
RIKEN Nishina Center, Wako
A highly sensitive beam current (position) monitor with a high Tc (Critical Temperature) SQUID (Superconducting QUantum Interference Device) and current sensor – the HTc-SQUID monitor – has been developed for the RIBF (RI Beam Factory) in RIKEN. In the present work, the HTc-SQUID monitor allows us to measure the DC of high-energy heavy-ion beams nondestructively in such a way that the beams are diagnosed in real time and the beam current extracted from the cyclotron can be recorded without interrupting the beam user's experiments. Both the HTc magnetic shield and the HTc current sensor were dip-coated with a thin layer of Bi-Sr-Ca-Cu-O (2223-phase, Tc 106 K) on 99.9 % MgO ceramic substrates. Unlike other existing facilities, all these HTS fabrications are cooled by a low-vibration pulse-tube refrigerator. These technologies enable us to downsize the system. Last year, aiming at the practical use, the HTc-SQUID monitor was installed in the RIBF. As a result, a 1 uA Xe beam intensity (50 MeV/u) was successfully measured with a 100 nA resolution. We will report the present status of the facility, the details of the monitor system and the results of the beam measurement.
PSI, Villigen
The 9th European Workshop on Beam Diagnostics and Instrumentation for Particle Accelerators (DIPAC 2009) was hosted by Paul Scherrer Institute (PSI) and took place at the Hotel Mercure Conference Center in Basel, Switzerland, May 25-27, 2009. A record number of 210 registered participants contributed to an exciting scientific program with ten invited talks, fourteen contributed orals and 115 poster contributions. In this talk, I will provide an overview of the various fields of beam instrumentation discussed during the workshop. A number of highlights from the scientific program have been selected, illustrating some of the outstanding achievements in accelerator diagnostics, presented at DIPAC 2009.