Modern circular and linear accelerators often rely on fast beam position feedbacks for the achievement of their design parameters. Such systems have gone through a significant evolution, which has taken advantage of recent progress of the associated equipment, like beam position monitors, as well as of the hardware and software processing technologies. A review of the latest developments and foreseen designs at different accelerators is given.

The project of a fast feedback system to stabilize the closed orbit of the Elettra storage ring is in an advanced stage. All of the existing BPMs have been equipped with new digital detectors in order to provide precise and high rate position measurements to the feedback system. A new beam position interlock system has also been installed to protect the vacuum chamber from synchrotron radiation produced by insertion devices. This paper presents features and performance of the new orbit measurement system and reports some preliminary results of the feedback commissioning.

A fast orbit feedback system has been installed at Elettra. It globally corrects the closed orbit at 10 kHz rate using all the BPMs and corrector magnets of the storage ring. Libera Electron has been chosen to upgrade the original detectors in order to provide micrometric accuracy and fast data rate of the beam position measurements. The article reports the experience gained during the commissioning of the system and the first operational results.

A fast digital feedback system is under development to stabilize the electron beam closed orbit at the Elettra storage ring. In view of the implementation of the feedback, the existing orbit measurement system is being upgraded to allow for better accuracy in the beam position measurement and higher acquisition rate. A global correction algorithm running on a number of distributed processing units will correct the orbit using all of the storage ring steerer magnets. The status of the project development is given in this article.

We describe the conceptual design and major performance parameters for the FERMI@Elettra Free Electron Laser (FEL) project funded for construction at Sincrotrone Trieste, Italy. This user facility complements the existing storage ring light source at Sincrotrone Trieste, and will be the first facility to be based on seeded harmonic cascade FELs. Seeded FELs provide high peak power pulses, with controlled temporal duration of the coherent output allowing tailored x-ray output for time domain explorations with short pulses of 100 fs or less, and high resolution with output bandwidths of the order of meV. The facility uses the existing 1.2 GeV S-band linac, driven by electron beam from a new highbrightness RF photocathode gun, and will provide tunable output over a range from ~100 nm to ~10 nm, and APPLE undulator radiators allow control of x-ray polarization. Initially, two FEL cascades are planned, a single-stage harmonic generation to operate over ~100 nm to ~40 nm, and a two-stage cascade operating from ~40 nm to ~10 nm or shorter wavelengh, each with spatially and temporally coherent output, and peak power in the GW range.

Following the installation of a number of fast local orbit fee dback systems, a global orbit feedback has been designed that will take advantage of all of the Beam Position Monitors (BPM) and corrector magnets of the ELETTRA storage ring. The existing beam position measurement system will be upgraded with digital detector electronics providing position mea surements with sub-micron resolution and fast data rate. A distributed processing syste m based on twelve stations equipped with standard VME CPU boards will share position data by means of a r eal-time fiber optic network. This article describes the architecture of the system and the results of simulations carried out using a model of the machine.

We describe the machine layout and major performance parameters for the FERMI FEL project funded for construction at Sincrotrone Trieste, Italy, within the next five years. The project will be the first user facility based on seeded harmonic cascade FELs, providing controlled, high peak-power pulses. With a high-brightness rf photocathode gun, and using the existing 1.2 GeV S-band linac, the facility will provide tunable output over a range from {approx}100 nm to {approx}10nm, with pulse duration from 40 fs to {approx} 1 ps, peak power GW, and with fully variable output polarization. Initially, two FEL cascades are planned; a single-stage harmonic generation to operate >40 nm, and a two stage cascade operating from {approx}40 nm to {approx}10 nm or shorter wavelength. The output is spatially and temporally coherent, with peak power in the GW range. Lasers provide modulation to the electron beam, as well as driving the photocathode and other systems, and the facility will integrate laser systems with the accelerator infrastructure, including a state-of-the-art optical timing system providing synchronization of rf signals, lasers, and x-ray pulses. Major systems and overall facility layout are described, and key performance parameters summarized.

We describe the machine layout and major performance parameters for the FERMI FEL project funded for construction at Sincrotrone Trieste, Italy, within the next five years. The project will be the first user facility based on seeded harmonic cascade FEL’s, providing controlled, high peak-power pulses. With a high-brightness rf photocathode gun, and using the existing 1.2 GeV S-band linac, the facility will provide tunable output over a range from ~100 nm to ~10 nm, with pulse duration from 40 fs to ~ 1ps, peak power ~GW, and with fully variable output polarization. Initially, two FEL cascades are planned; a single-stage harmonic generation to operate > 40 nm, and a twostage cascade operating from ~40 nm to ~10 nm or shorter wavelength. The output is spatially and temporally coherent, with peak power in the GW range. Lasers provide modulation to the electron beam, as well as driving the photocathode and other systems, and the facility will integrate laser systems with the accelerator infrastructure, including a state-of-the-art optical timing system providing synchronization of rf signals, lasers, and x-ray pulses. Major systems and overall facility layout are described, and key performance parameters summarized. OVERVIEW OF THE FACILITY The FERMI @ Elettra facility will make use of the existing GeV linac at Sincrotrone Elettra, which will become available for dedicated FEL applications following the completion of construction of a new injector booster complex for the storage ring. With a new rf photocathode injector, and some additional accelerating sections, this linac will be capable of providing high brightness bunches at 1.2 GeV and up to 50 Hz repetition rates. Figure 1 shows a preliminary CAD drawing of the proposed facility, with the linacbased FEL facility adjacent to the Elettra storage ring building. To accommodate the new rf photocathode gun, the tunnel which houses the existing linac and thermionic gun will be extended upstream. This will be a relatively minor investment in additional excavation and will take advantage of the present roadway cutting, already at the level of the linac and extending backward several meters. An S-band rf photocathode gun, with spatial and temporal control of the photocathode laser system, will provide high brightness electron bunches at up to 50 Hz rate. Flexibility in bunch parameters will be incorporated into the systems design. Accelerating sections raise the beam energy to ~100 MeV at the exit of the injector. A laser heater system following the injector system will provide control of the uncorrelated energy spread in the beam and minimize potential impact of the microbunching instability. The laser heater also allows opportunity for implementing useful diagnostics systems. Two magnetic bunch compressors are planned, inserted at 230 MeV and at 650 MeV. The final energy of the beam, 1.2 GeV, is determined by the accelerator section maximum gradient, available RF power including overhead and de-rating for reliable operations, and off-crest operation for control of energy chirp. The linac is installed in a tunnel about 5 m below ground level, and the new facility will include a transport line to take the beam up to an undulator hall at or near the surface. This vertical ramp allows inclusion of useful diagnostics, and is carefully designed to minimize perturbations to the beam quality. In the undulator hall, the electron beam may be directed to the longer-wavelength FEL (FEL-I) by a transport line which introduces a horizontal offset to the beam, or to the short-wavelength FEL (FEL-II) in a direct line to avoid perturbation to beam quality due to CSR in bend magnets. A timing system based on transmission of optical signals over a highly stabilized fiber optic system will distribute timing signals throughout the facility. This provides synchronization of the photocathode laser to the RF gun phase, stabilized drive signals to RF systems in the facility, and synchronization of the FEL seed laser with the arrival time of the electron beam. The seeded FEL process occurs in one stage of harmonic generation for FEL-I, and in a two-stage cascade for FEL-II. For FEL-II, both a fresh-bunch approach and a whole-bunch seeding technique are being developed. The x-ray pulse duration is determined by the seed laser, and both short-pulse (~40-100 fs) and long pulse (~0.5-1.0 ps) schemes are under development. The photon beams from the FELs are transported in beamlines to hutches an adjoining downstream experimental hall. The electron beams are dumped following the final radiating undulator. Laser systems in the experimental area are synchronized to the FEL output using the stabilized optical timing system distributed around the facility. Figure 1: The FERMI FEL facility shown adjacent to the existing synchrotron radiation source Elettra. Figure 2 shows the machine layout with various sections identified; INJ – injector, L1-L4 – linac sections, BC1,2 bunch compressors, MTC1,2 – matching section, RAMP – vertical transport line, SPRD – beam spreader section, FEL1,2 – FEL’s.

During the last year, the third generation synchrotron light source ELETTRA could fully benefit of several upgrades that have been implemented in the frame of a project to enhance the quality of the light source. The super conducting third harmonic cavity, the feedbacks, the realignment of the whole ring and other improved devices have allowed to further, significantly optimize the beam stability and lifetime, as well as the operability and uptime of the facility. At the same time two large-scale projects are underway that will change the perspectives of the whole ELETTRA laboratory, namely the full energy booster injector and the single pass X-ray FEL FERMI@Elettra, based on the existing linac. Their status will be presented here together with the overview of the existing light source.

Following the installation of a number of fast local orbit fee dback systems, a global orbit feedback has been designed that will take advantage of all of the Beam Position Monitors (BPM) and corrector magnets of the ELETTRA storage ring. The existing beam position measurement system will be upgraded with digital detector electronics providing position mea surements with sub-micron resolution and fast data rate. A distributed processing syste m based on twelve stations equipped with standard VME CPU boards will share position data by means of a r eal-time fiber optic network. This article describes the architecture of the system and the results of simulations carried out using a model of the machine.

A new injector made of a 100 MeV Linac and a 2.5 GeV booster ring is being built at ELETTRA to provide full energy injection into the storage ring in top-up mode. This project has required a novel design of the control system with the adoption of a new architecture and the use of up to date technologies, which will also be the basis of the control systems for future projects and accelerators upgrades. In this context, ELETTRA has adopted Tango as the control system software framework and has joined the Tango collaboration as a developer partner. The main aspects regarding the control system structure, the development of graphical user interfaces and the technical solutions adopted for the equipment interfaces are discussed. Use of industrial controllers for the interlock and personnel safety systems and their integration into the control system are also presented in this article.

Sincrotrone Trieste has received funding and has begun the final refinement of technical parameters as well as the construction of a new Free Electron Laser (FEL) called Fermi. The new light source will be located adjacent to the existing Elettra storage ring and will use the linac that presently injects electrons into this light source. The linac will shortly become fully available to the Fermi project as a new dedicated full energy injection system is also being built for Elettra. Why are VUV and X-ray FELs so important and how do they work? Most readers will know that in a bending magnet, synchrotron radiation is created by the incoherent emission of each electron as it moves in a magnetic field.

A number of fast local orbit feedback stations are being sequentially installed at ELETTRA to improve the stability of the electron beam at the Insertion Device (ID) source points. They rely on electron Beam Position Monitors equipped with digital detector electronics that provides high precision and readout rate. The local feedback stations will be integrated in a fast global orbit feedback system, which is the goal of the ongoing developments. The performance and the operational experience gained with the local feedback systems are presented.

The temporal structure of the storage-ring free-electron laser at Elettra shows high sensitivity to electron-beam instabilities. In fact, even small beam perturbations may affect the FEL dynamics and periodically switch off the laser. In order to improve the FEL operation and performance, different and complementary feedback systems have been activated. This paper reports on their beneficial effect. Plans for future improvements are also briefly outlined.

As is well known, the stability of a storage-ring free- electron laser is strongly related to that of the electron beam. With respect to second-generation sources, such as Super ACO and UVSOR, the free-electron laser at ELET- TRA is characterized by a noticeably higher gain and, therefore, shows to be much more sensitive to electron- beam instabilities. In order to counteract the impact of such instabilities, both a longitudinal multibunch and a local or- bit feedback have been activated during free-electron laser operation. Aim of this paper is to report on the beneficial effect of these feedback systems on the laser performance.

Bunch-by-bunch feedback systems have been installed at ELETTRA to counteract coupled-bunch instabilities. Following a novel approach both the transverse and the longitudinal systems rely on the same type of programmable digital processing electronics executing the proper software. After a description of the overall machine scenario in which the transverse systems are operated, the status of the longitudinal feedback commissioning is given

The ELETTRA control system front-end computers are presently based on 68k VME boards and the OS-9 operating system. In view of the construction of the new booster injector and of a smooth upgrade of the existing control system, PowerPC VME boards running Linux have been adopted. The new platform provides reliability, performance and flexibility, while the RTAI (Real Time Application Interface) extension offers, where necessary, satisfying real-time capabilities that compete well with those of the most popular real-time operating systems. This article describes the main issues associated to the choices we made and presents an example of application.