Y. Chung

Digital closed orbit feedback system for the advanced photon source storage ring

The Advanced Photon Source (APS) is a dedicated third-generation synchrotron light source with a nominal energy of 7 GeV and a circumference of 1104 m. The closed orbit feedback system for the APS storage ring employs unified global and local feedback systems for stabilization of particle and photon beams based on digital signal processing (DSP). Hardware and software aspects of the system will be described in this paper. In particular, we will discuss global and local orbit feedback algorithms, PID (proportional, integral, and derivative) control algorithm, application of digital signal processing to compensate for vacuum chamber eddy current effects, resolution of the interaction between global and local systems through decoupling, self-correction of the local bump closure error, user interface through the APS control system, and system performance in the frequency and time domains. The system hardware including the DSPs is distributed in 20 VME crates around the ring, and the entire feedback system runs synchronously at 4-kHz sampling frequency in order to achieve a correction bandwidth exceeding 100 Hz. The required data sharing between the global and local feedback systems is facilitated via the use of fiber-optically-networked reflective memories.

Performance of the beam position monitor for the Advanced Photon Source

Performance measurement and analysis of the Advanced Photon Source (APS) beam position monitor (BPM) electronics are reported. The results indicate a BPM resolution of 0.16 μm⋅mA/√Hz in terms of the single‐bunch current and BPM bandwidth. For the miniature insertion device (ID) BPM, the result was 0.1 μm⋅mA/√Hz. The improvement is due to the 3.6 times higher position sensitivity (in the vertical plane), which is partially canceled by the lower button signal by a factor of 2.3. The minimum single‐bunch current required was roughly 0.03 mA. The long‐term drift of the BPM electronics independent of the actual beam motion has measured at 2 μm/hr, which settled after approximately 1.5 hours. This drift can be attributed mainly to the temperature effect. Implications of the BPM resolution limit on the global and local orbit feedback systems for the APS storage ring will also be discussed.

Beam position monitor data acquisition for the Advanced Photon Source

This paper describes the beam position monitor (BPM) data acquisition scheme for the Advanced Photon Source (APS) storage ring. The storage ring contains 360 beam position monitors distributed around its 1104-meter circumference. The beam position monitor data acquisition system is capable of making turn-by-turn measurements of all BPMs simultaneously. It is VXI-based with each VXI crate containing the electronics for 9 BPMs. The VXI local bus is used to provide sustained data transfer rates of up to 13 mega-transfers per second to a scanner module. The system provides single-bunch tracking, bunch-to-bunch measurements, fast digital-averaged positions, beam position history buffering, and synchronized multi-turn measurements. Data is accessible to the control system VME crates via an MXI bus. Dedicated high-speed ports are provided to supply position data to beam orbit feedback systems.<<ETX>>

Test results of a monopulse beam position monitor for the Advanced Photon Source

A prototype of the Monopulse Beam Position Monitor (BPM) was tested to determine the resolution capability for various signal levels and beam configurations. The BPM was tested in two environments: using a wire simulation of the beam in the laboratory and using real beam at various positions and levels at Stanford Synchrotron Radiation Laboratory. Both tests showed a resolution capability of better than 25 microns. This paper presents the procedures and measurements’ results.

Overview of charged‐particle beam diagnostics for the advanced photon source (APS)

Plans, prototypes, and initial test results for the charged-particle beam (e[sup [minus]],e[sup +]) diagnostic systems on the injector rings, their transport lines, and the storage ring for the Advanced Photon Source (APS) are presented. The APS will be a synchrotron radiation user facility with one of the worlds brightest x-ray sources in the 10-keV to 100-keV regime. Its 200-MeV electron linac, 450-MeV positron linac, positron accumulator ring, 7-GeV booster synchrotron, 7-GeV storage ring, and undulator test lines will also demand the development and demonstration of key particle-beam characterization techniques over a wide range of parameter space. Some of these parameter values overlap or approach those projected for fourth generation light sources (linac-driven FELs and high brightness storage rings) as described at a recent workshop. Initial results from the diagnostics prototypes on the linac test stand operating at 45-MeV include current monitor data, beam loss monitor data, and video digitization using VME architecture.

Theoretical studies on the beam position measurement with button-type pickups in APS

The response of electrostatic button-type pickups for the measurement of the transverse position of charged particle beams was investigated and analytical formulas were obtained for the signal as a function of time and the coordinates of the beam and the electrodes. The study was done for beam pipes, for rectangular and non-rectangular electrodes, and for several cases of longitudinal beam profiles. The numerical results show good agreement with the analytical results, except that the presence of the photon beam channel and the antechamber causes finite offset ( approximately 20 mu m) of the electrical center in the horizontal direction. Time domain analysis indicates that the error in the measurement of the beam position using circular electrodes as compared to rectangular ones was found to be less than 100 mu m per 1 cm of beam excursion from the center of the beam pipe for the case of the Advanced Photon Source (APS) storage ring vacuum chamber.<<ETX>>

Configuration and test of the APS storage ring beam position monitor electronics

This paper will present the final tests of the APS storage ring BPM electronic system. The final configuration includes the filter‐comparator installed in the accelerator tunnel and the signal conditioning and digitizing unit (SCDU) in a VXI configuration. The SCDU includes an AM/PM monopulse receiver at 352 MHz. Extensive testing was performed on the system. The key parameters measured were the null cancellation better than 45 db, dynamic range of better than 40 db, single bunch capability with 0.01 mA sensitivity, and a resolution better than 10 micron for 512 averaged turns. This last critical performance was tested using a moving wire to simulate the beam. This report will concentrate on the wire test results. Also, the actual production hardware will be presented.

Local beam position feedback experiments on the ESRF storage ring

This paper describes the results of local beam position feedback experiments conducted on the ESRF storage ring using digital signal processing (DSP) under the trilateral agreement of collaboration among ESRF, APS, and SPring-8. Two RF beam position monitors (BPMs) in the upstream and downstream of the insertion device (ID) and two X-ray BPMs in the sixth cell were used to monitor the electron beam and the X-ray beam emitted from the ID, respectively. The local bump coefficients were obtained using the technique of singular value decomposition (SVD) on the global response matrix for the bump magnets and all the available BPMs outside the local bump. The local response matrix was then obtained between the two three-magnet bumps and the position monitors. The data sampling frequency was 4 kHz and a proportional, integral, and derivative (PID) controller was used. The result indicates the closed-loop feedback bandwidth close to 100 Hz and clear attenuation (/spl ap/-40 dB) of the 7-Hz beam motion due to girder vibration resonance. Comparison of the results using the RF BPMs and X-ray BPMs will be also discussed.

Overall design concepts for the APS storage ring machine protection system

The basic design and status of the machine protection system for the Advanced Photon Source (APS) storage ring are discussed. The machine is passively safe to the bending magnet sources, but the high power of the insertion devices requires missteering conditions to be identified and the beam aborted in less than one millisecond. The basic aspects of water flow, temperature, beam position, etc. monitoring are addressed. Initial commissioning of subsystems and sensors is statused.

Measurement of beta-function and phase using the response matrix

A new method for extracting the beta-function and phase for the beam position monitors (BPMs) and the corrector magnets from the measured response matrix is presented. The response matrix relates beam motion at the BPM locations to changes in corrector magnet strengths. Using the model beta and phase as the initial values, new values are obtained by iteration. The accuracy of beta and phase thus calculated is limited by the accuracy of response matrix measurement and calibration of BPMs and correctors. The scaling ambiguity in the beta-function is resolved by matching the beta product and phase advance across a drift region. A by-product of this technique is an accurate determination of the betatron tune, and in principle, quadrupole strengths can be calculated from the betas and phases. This method is applied to data obtained from the X-ray ring at the National Synchrotron Light Source at Brookhaven. The possibility of applying the results to lattice-debugging will also be discussed.<<ETX>>