At the x-ray free-electron laser SwissFEL, at the Paul Scherrer Institute, Switzerland, beam loss monitors are used to determine loss positions along the linear accelerator and protect critical elements such as the undulator magnets from excess radiation. These monitors are integrated into the machine protection system (MPS) allowing beam losses to be limited by dynamically reducing the repetition rate. This paper focuses on the types of loss monitors installed at SwissFEL and their function in protecting the machine.

The SwissFEL Injector Test Facility operated at the Paul Scherrer Institute between 2010 and 2014, serving as a pilot plant and testbed for the development and realization of SwissFEL, the X-ray Free-Electron Laser facility under construction at the same institute. The test facility consisted of a laser-driven rf electron gun followed by an S-band booster linac, a magnetic bunch compression chicane and a diagnostic section including a transverse deflecting rf cavity. It delivered electron bunches of up to 200 pC charge and up to 250 MeV beam energy at a repetition rate of 10 Hz. The measurements performed at the test facility not only demonstrated the beam parameters required to drive the first stage of an FEL facility, but also led to significant advances in instrumentation technologies, beam characterization methods and the generation, transport and compression of ultra-low-emittance beams. We give a comprehensive overview of the commissioning experience of the principal subsystems and the beam physics measurements performed during the operation of the test facility, including the results of the test of an in-vacuum undulator prototype generating radiation in the vacuum ultraviolet and optical range.

SwissFEL will provide users with brilliant X-ray pulses in 2017. A comprehensive suite of diagnostics is needed for the initial commissioning, for changes to the operating point, and for feedbacks. The development of instrumentation for SwissFEL is well underway, and solutions have been identified for most diagnostics systems. I will present here an overview of the instrumentation for SwissFEL, and give details on some recent developments.

PSI has developed a signal processing VXS/VME64x board for accelerator applications like low-latency bunchto-bunch feedbacks, global orbit feedbacks or low-level RF systems. The board is a joint development of PSI/SLS staff and staff working on the contribution of PSI for the European X-ray FEL (E-XFEL). Future applications of the board include the Intra-Bunch-Train Feedback (IBFB) [1] of the E-XFEL as well as the upgrade of the SLS Fast Orbit Feedback (FOFB) and Multibunch Feedback (MBFB). The PDC board has four Virtex-4 FPGAs, two TS201 Tiger Sharc DSPs, VXS and VME64x 2eSST interfaces, and two front panel SFP multi-gigabit fibre optic links. Two 500-pin LVDS/multi-gigabit mezzanine connectors allow to interface the FPGAs to two application-dependent mezzanine modules each containing e.g. four 500MSPS 12-bit ADCs and two 14bit DACs for the IBFB and MBFB, or four multi-gigabit SFP fibre optic transceivers for the FOFB. This paper reports on hardware and firmware concepts, system topologies and synergies of future applications. HARDWARE ARCHITECTURE FPGA-Based Low-Latency Feedbacks Two Virtex-4 SX FPGAs (“Feedback FPGAs”) on the PDC allow to perform bunch-to-bunch feedback algorithms by receiving beam position monitor (BPM) data from the ADCs of the above mentioned mezzanine, calculating suitable correction kicks, and writing the kick amplitudes to the DACs that drive the kicker amplifiers. With suitable low-latency BPM and kicker electronics and optimised cabling, overall feedback loop latencies in the order of 200ns which is the bunch spacing of the 600μs long E-XFEL bunch trains are feasible. In case of the E-XFEL IBFB the main requirements for ADCs and DACs are a low latency ideally far below the 200ns bunch spacing, while the sample rate is less critical. However, the chosen maximum sample rate of 500MSPS allows the ADC/DAC mezzanine and PDC also to be used for storage ring MBFBs with bunch spacings down to 2 ns and required overall loop latencies of e.g. ~1μs for the SLS. One programmable on-board clock phase shifter with ~10ps step size and ~10ns range for each ADC and DAC allows to adjust the sample phases for MBFB applications for minimal position measurement and kicker crosstalk of adjacent bunches. In case of the IBFB, the clock shifters allow e.g. to sample exactly on the top of the short output pulses of low-latency BPM RF front-ends (RFFEs), thus minimising clock jitter impact. PD C” VM E Crrier Bard Pigyback Bards

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 optimization 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.

After joining the preparatory phase of the European X- FEL project, the Paul Scherrer Institut 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 facility at DESY. The IBFB will make use of the long bunch trains provided by the superconducting drive accelerators of FLASH as well as the European X-FEL allowing to damp beam motions in a frequency range of a few kHz up to several hundreds of kHz applying modern control algorithms in a feedback loop. The FPGA-based, digital data processing and the low latency time (preferably < 200 ns) permit the elimination of long range (from bunch train to bunch train) and ultra fast (bunch by bunch) repetitive beam movements by adaptive feed forwards. In this paper, we will introduce the IBFB design concept and report on first test measurements with newly designed stripline beam position monitors for the FLASH facility.

The large variety of measurement applications for the PSI accelerator diagnostics section leads to a modular approach in electronics design. The backbone of such a concept is the so called “VME generic PMC carrier board” (VPC), which is acting as a highly flexible data processing and communication unit between customized front end electronics and the standardized VME control system. The VPC specifications and design concept, which was elaborated with in the DACSY initiative at PSI is presented and a short status of the project is given in this paper.

This report gives an overview of the design concept and applications of the VME PMC Carrier board (VPC), a VME64x board that was developed at PSI as a common digital back-end for beam instrumentation at the PSI electron and proton accelerators. The two Xilinx Virtex2Pro FPGAs of the VPC allow the implementation of the complete digital section of a beam instrumentation system on a single chip ("SOC"), including detector frontend interface, filters, interlocks, feedback links, high-level data analysis like FFTs, and a generic control system interface. In addition to the two on-chip PowerPC processors of the FPGAs, the VPC provides a DSP, RAM, and multi-gigabit fibre optic links for distributed feedbacks and synchronisation. First applications of the VPC include digital proton beam position monitors (DBPMs) and beam profile monitors for the PSI proton accelerators, the readout of several thousand detector channel waveforms for a muon decay experiment, and the integration of photon BPMs into the SLS fast orbit feedback (FOFB). In addition to a status report and first results for these applications, an outlook on possible future applications of the VPC will be given.

Rapid progress in digital electronics allows digitisation of monitor signals at a very early stage of the signal processing chain, providing optimum performance and maximum flexibility for today’s accelerator instrumentation. While the analog front-ends of such systems are usually specific for each monitor type, the subsequent digital part of the processing chain can be unified for many different measurement tasks. The “generic VME PMC Carrier board” (VPC) [1] was developed to achieve this unification for the PSI electron and proton accelerator diagnostics and fast data acquisition and feedback systems. The core of the VME64x board consists of two Virtex2Pro FPGAs with two PowerPCs each, a floating point DSP and RAM. The FPGAs can acquire and process measurement data from the VMEbus P0/P2 connectors or from two applicationdependent PMC mezzanine modules. Two 2 GBaud fibre optics transceivers may also be used to acquire or distribute measurement data. Envisaged applications include digital beam position (DBPM) and current monitors for proton beams, data processing for a muon decay experiment, and general beam diagnostics as well as global feedbacks at SLS accelerators and beamlines.

Within the frame of the project for a multi bunch feedback system for the Swiss Light Source (SLS), a new family of 500 MS/s analog to digital and digital to analog conversion boards with an 8 bit resolution has been developed, containingon-boardMUX andDEMUX circuitryto reduce data rates to approximately 20 MS/s using up to twelve Front Panel Data Ports (FPDP). Using six quad processor DSP boards, full bandwidth bunch by bunch feedbacks in the transverse and longitudinal planes are set up to provide bunch by bunch correction kicks wit ha2n sresolution. We report on the hardware setup and properties as well as feedback performance in the SLS storage ring.

A global, fast orbit feedback (FOFB) based on the digital beam position monitor (DBPM) system has been in user operation at the Swiss Light Source (SLS) since November 2003. The SVD‐based correction scheme acts at a sampling rate of 4 kHz using position information from all 72 DBPM stations and applying corrections with all 72 horizontal and 72 vertical corrector magnets. As a result, the FOFB successfully damps orbit distortions, which are mainly caused by ground and girder vibrations as well as the 3‐Hz booster crosstalk. It also allows fast and independent ID gap changes, which are completely transparent to all SLS users. With top‐up as a regular operation mode at SLS, global beam stability on a μm‐level has been achieved from days to milliseconds.

The SLS Fast Orbit Feedback (FOFB) was successfully commissioned in 2003 (1). Since November 2003 it runs during user operation of the SLS. Taking into account 72 Digital Beam Position Monitors (DBPMs), the FOFB ap- plies SVD-based global orbit corrections for 72 horizontal (x) and 72 vertical (y) correctors at a rate of 4 kHz, com- pared to 0.5 Hz for the Slow Orbit Feedback (SOFB) that was used so far. While the SOFB was important for the elimination of orbit drifts due to temperature changes and slowly moving insertion device (ID) gaps, the FOFB is also able to damp orbit oscillations that are caused by fast changes of ID gaps or magnets, by ground and girder vibrations, 3 Hz booster crosstalk and power supply noise. This report presents experience from commissioning and user operation of the FOFB.

Precise orbit control is one of the crucial ingredients for stable operation of the SLS storage ring. The orbits are taken by the digital BPM system which allows beam position measurements to the sub-micron level at sampling rates of up to 4 kHz at 72 locations in the ring. Orbits are corrected with respect to a user defined reference by applying SVD techniques and a direct response matrix inversion. A slow global orbit feedback operating at correction rates of up to 1 Hz stabilizes the orbit to within ∼0.5 µm rms at the locations of the insertion devices. Energy drifts are automatically corrected using the RF frequency as an additional corrector, resulting in a long term energy stability of σ(dP/P) ≈ 10 −5 . The status of a digital BPM system based fast orbit feedback running at 4 kHz sampling rate is presented.

The accelerator complex of the Swiss Light Source (SLS) is presently under commissioning at the Paul Scherrer Institute (PSI) in Villigen, Switzerland. The newly developed digital beam position monitor (DBPM) system has been successfully used to determine beam positions in the pre-injector LINAC, the transfer lines, the booster synchrotron and the storage ring. Instant and free selection of operation modes through the EPICS-based SLS control system allows to choose between single turn, turn-by-turn and closed orbit measurements. The operational experience and performance of the DBPM system is presented, based on measurements, taken during SLS commissioning. A monitoring system (POMS), which measures the horizontal and vertical mechanical positions of each BPM block in reference to the adjacent quadrupole magnets has been installed and first results, indicating transverse movements of the BPM blocks as a function of current in the storage ring will be presented.

The paper presents first operational experience with the new digital beam position monitoring system (DBPM) for the Swiss Light Source (SLS). The system permits for the first time to have a single position monitoring system that measures both the slow and the fast aspects of beam position. When the electronics is set to "slow", the DBPM allows position measurements with high precision, stability and reproducibility and is ideally suited for closed orbit measurements and feedback systems. When set to "fast", the DBPM turns into a powerful beam dynamics tool that permits to extract more dynamic parameters of the beam/machine from turn-by-turn position readings. The key strengths of the system is its programmability that delivers an arbitrary FIR low pass transfer function with a bandwidth spanning from few hundred Hz to over 1 MHz, good reproducibility obtained through the use of a pilot signal and excellent linearity that relies on the direct sampling of the intermediate frequency signal (IF). The core components of the system are the RF front end, the digital receiver and the DSP board, which are all housed in a VME crate. The interface to the EPICS control system at SLS is done via an Input/Output Controller, which resides in the same crate.

A prototype Low Gap BPM system has been installed at ELETTRA and it is now undergoing the first tests. The main purpose of this system is to provide ultra-stable position signals, at the micrometer level, to the Orbit Feedback processors. The system consists of a new Low Gap monitor and a new digital BPM electronics. The monitor was designed at ELETTRA and fits to the 14 mm low gap ID vacuum chamber. Full advantage has been taken from the reduced gap button distance. To reach maximum stability of the BPM itself, a new support system has been designed where, by means of two bellows, the BPM movements are de-coupled from the vacuum chamber slow drifts. Furthermore an external system monitors the BPM position with respect to a reference column made of carbonium. The Low Gap BPM system adopts the digital BPM electronics that was conceived at the Paul Scherrer Institut for the Swiss Light Source (SLS). One of its features is the programmable bandwidth that offers sub-micron position data when set to low bandwidth (<1 kHz). The project evolved into a successful collaborative development between ELETTRA, APL, SLS and the company Instrumentation Technologies. In this paper the first results obtained on the ELETTRA Storage Ring are presented and future system integration is outlined.

The design, construction and performance of the H1 silicon vertex detector is described. It consists of two cylindrical layers of double-sided, double-metal silicon sensors read out by a custom designed analog pipeline chip. The analog signals are transmitted by optical fibres to a custom-designed ADC board and are reduced on PowerPC processors. Details of the design and construction are given and performance figures from the first data-taking periods are presented.

The layout of the SLS beam position monitor (BPM) system is presented. Since sub-micron position data in normal closed orbit and feedback mode as well as turn by turn information are required, the SLS BPM electronics pursues a new digital approach. The self calibrating four channel system consists of a RF front end, a digital receiver and a DSP controller. The whole system is integrated in the EPICS control system, which allows to select between different operation modes, so that the same BPM electronics applies to all the sections of the machine, namely linac, transfer lines, booster and storage ring. Mechanical drifts will be monitored by an independent measurement system and taken into account, when processing the final electron beam position

This paper presents a new digital beam position moni- tor (DBPM) system which is currently under develop- ment for the Swiss Light Source (SLS). It is designed to provide sub-micron position data in normal closed orbit, and feedback mode as well as turn by turn information for machine studies and real time tune measurements. The self calibrating four channel system consists of a RF front end, a digital receiver and a DSP module. The same electronics will be used in all sections of the SLS accel- erator complex. The system can be reconfigured in real time to perform different kind of measurements like: pulsed for linac and transfer lines, first turn, turn-by-turn, closed orbit, feedback and even tune mode for booster and storage ring. These reconfigurations only involve downloading of new signal processing software and will be performed via EPICS control system. An independent system for monitoring mechanical drifts of the BPM sta- tions will be installed as well. The measured data will be permanently updated in a database and taken into ac- count, when processing the final electron beam positions.