SOLEIL, Gif-sur-Yvette
Beam orbit stability is a crucial parameter for 3rd generation light sources in order to achieve their optimum performance. Sub-micron stability is now a common requirement for vertical beam position. To reach such performance, Global Orbit Feedback Systems are mandatory. This paper describes the different design approaches for Global Orbit Feedback Systems. A few machines can use a single set of strong correctors. Most machines have their strong corrector bandwidth limited by eddy currents in aluminium vacuum chamber, or power-supplies speed or digitization granularity. Then, a second set of fast correctors is required for high frequency correction. But Fast and Slow Orbit Feedback Systems cannot work together with a common frequency range, they fight each other. An earlier solution has been to separate fast and slow systems by a frequency deadband. This approach does not allow correcting efficiently the orbit shift due to the gap movements of the increasingly sophisticated insertion devices that are installed on new machines. The different solutions that have been recently implemented are reviewed.
DELTA, Dortmund
The beam orbit of the 1.5GeV electron storage ring DELTA showed a variety of beam distortions with a pronounced frequency spectrum mostly caused by girder movements and ripples of the magnet power supplies. In order to enhance the orbit stability at least up to 300 Hz bandwidth a global fast orbit feedback is under consideration. As a prototype an FPGA based local fast orbit feedback at a 10 kHz data acquisition rate has been developed. The digitized orbit data are distributed from I-Tech Libera and Bergoz MX-BPMs to an FPGA board via a fibre interconnected network based on the Diamond Communication Controller [*]. The correction algorithm is written in VHDL and the corrections are applied with digital power supplies connected to the FPGA board through RS485 links. The first operational tests of the system achieved an effective damping of orbit distortions up to 350 Hz. The paper will give an overview on the layout of the FPGA based local orbit feedback system, will report on the results of the measured uncorrected orbit distortions at DELTA and the stability enhancements that could be achieved by the local feedback system.
* I. S. Uzun et al., "Initial Design of the Fast Orbit Feedback System for
Diamond Light Source", Proc. 10th ICALEPCS
DESY, Hamburg
For current and future accelerators, in particular light sources, high availability is an important topic. Therefore the causes of beam losses must be diagnosed and eliminated as fast as possible. This paper presents a concept using the following signals and data from diagnostic instruments and other sources:
- software alarms transmitted by the control system,
- hardware alarms received and timestamped by the machine protection system, and
- Post-Mortem-Analysis.
PSI, Villigen
The PSI 250 MeV Injector, a precursor to the SwissFEL with its extreme jitter and stability demands poses new challenges for the synchronization system. Our concept is double-tracked: low risk electrical and best potential performance and flexibility optical. The electrical distribution system, being established first, relies on reliable technology. Optimized to achieve a benchmark jitter performance of around 10fs and a long term drift stability of some 10fs in the most critical parts of the machine it will also backup the optical system. Sub 10fs jitter and drift figures are being aspired for the latter. In this contribution, both systems are presented, measurements of electrical and optical reference signal jitter and long term cable and coupler drifts will be shown. A cable temperature stabilization system and the influence of mechanical noise will be discussed, too. Finally, first jitter measurements of the optical system will be presented.
ESRF, Grenoble
Until 2008, the suppression of the closed orbit distortion on the storage ring of the ESRF was obtained using two separate systems: A slow system using 224 BPM and 96 correctors performing a correction every 30 seconds, and a fast system, using only 32 BPMs and 32 correctors but working at 4.4KHz, damping the orbit distortion from 50mHz up to 150Hz; the 15mHz to 50mHz frequency span was left uncorrected. This separation of the frequency ranges of the two systems avoided cross talks between them, but prevented the efficient cancellation of the very low frequency orbit distortions caused by the frequent modification of the insertion device settings during the beamlines operation. We now coordinate the operation of the slow and fast systems and suppress this dead frequency span. This paper describes the principle and the beneficial effect of this new scheme, and its limitations. To overcome these limitations, we are now developing a single new orbit correction system which will damp the orbit distortion from DC to 150Hz; this system will use the Libera Brillance BPM electronics recently implemented at ESRF, and new fast correctors. This new scheme is also briefly presented.
NSRRC, Hsinchu
The BPM electronics of the Taiwan Light Source (TLS) have been upgraded to the Libera Brilliance in August 2008 to improve performance and functionality. Orbit feedback system is also migrated into fast orbit feedback system to enhance orbit stability. Infrastructure of the orbit acquisition system and orbit feedback system has been reconstructed to accommodate with new BPM electronics and satisfy requirements of fast orbit feedback loops. Gigabit Ethernet grouping was adopted for the data transfer rate of 10 kHz between BPM and the orbit feedback system. A summary of the efforts and performance of this upgrade will be presented in this report.
CERN, Geneva
Many beam instrumentation signals of large circular accelerators are in the kHz range and can thus be digitised with powerful high resolution ADCs. A particularly large dynamic range can be achieved if the signals are analysed in the frequency domain. This report presents a system employing audio ADCs and FPGA-based spectral analysis, initially developed for tune measurement applications. Technical choices allowing frequency domain dynamic ranges beyond 140 dB are summarised.