F. Lenkszus

Status and design of the Advanced Photon Source control system

This paper presents the current status of the Advanced Photon Source (APS) control system. It discusses the design decisions which led us to use industrial standards and collaborations with other laboratories to develop the APS control system. The system uses high performance graphic workstations and the X-windows graphical user interface (GUI) at the operator interface level. It connects to VME/VXI-based microprocessors at the field level using TCP/IP protocols over high performance networks. This strategy assures the flexibility and expansibility of the control system. A defined interface between the system components will allow the system to evolve with the direct addition of future, improved equipment and new capabilities.<<ETX>>

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.

Design and commissioning of the APS beam charge and current monitors

The non‐intercepting charge and current monitors suitable for a wide range of beam parameters have been developed and installed in the Advanced Photon Source (APS) low energy transport lines, positron accumulator ring (PAR), and injector synchrotron. The positron or electron beam pulse in the APS has charge ranging from 100 pC to 10 nC with pulse width varying from 30 ps to 30 ns. The beam charge and current are measured with a current transformer and subsequent current monitoring electronics based on an ultrafast, high precision gated integrator. The signal processing electronics, data acquisition, and communication with the control system are managed by a VME‐based system. This paper summarizes the hardware and software features of the systems. The results of recent operations are presented.

A bunch clock for the Advanced Photon Source

A bunch clock timing module has been developed for use by Advanced Photon Source beamlines. The module provides bunch pattern and timing information that can be used to trigger beamline data collection equipment. The module is fully integrated into the control system software (EPICS) which automatically loads it with the storage ring fill pattern at injection time. Fast timing outputs (1 ns FWHM) for each stored bunch are generated using the storage ring low-level rf and revolution clock as input references. Fiber-optic-based transmitters and receivers are used to transmit a 352-MHz low-level rf reference to distributed bunch clock modules. The bunch clock module is a single-width VME module and may be installed in a VME crate located near beamline instrumentation. A prototype has been in use on the SRI CAT beamline for over a year. The design and integration into the control system timing software along with measured performance results are presented.

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>>

Characterizing transverse beam dynamics at the APS storage ring using a dual-sweep streak camera.

We present a novel technique for characterizing transverse beam dynamics using a dual-sweep streak camera. The camera is used to record the front view of successive beam bunches and/or successive turns of the bunches. This extension of the dual-sweep technique makes it possible to display non-repeatable beam transverse motion in two fast and slow time scales of choice, and in a single shot. We present a study of a transverse multi-bunch instability in the APS storage ring. The positions, sizes, and shapes of 20 bunches (2.84 ns apart) in the train, in 3 to 14 successive turns (3.68 μs apart) are recorded in a single image, providing rich information about the unstable beam. These include the amplitude of the oscillation (∼0 mm at the head of the train and ∼2 mm towards the end of the train), the bunch-to-bunch phase difference, and the significant transverse size growth within the train. In the second example, the technique is used to characterize the injection kicker-induced beam motion, in support of th...

Commissioning of the APS real-time orbit feedback system

A unified global and local closed-orbit feedback system has been implemented at the Advanced Photon Source in order to stabilize both particle and photon beams. Beam stability requirements in the band up to 50 Hz are 17 /spl mu/m in the horizontal plane and 4.4 /spl mu/m vertically. Orbit feedback algorithms are implemented digitally using multiple digital signal processors, with computing power distributed in 20 VME crates around the storage ring. Each crate communicates with all others via a fast reflective memory network. The system has access to 320 RF beam position monitors together with X-ray beam position monitors in both insertion device and bending magnet beamlines. Up to 317 corrector magnets are available to the system. The global system reduces horizontal RMS beam motion at the X-ray source points by more than a factor of two in the frequency band from 10 mHz to 50 Hz.

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.

New APS storage ring BPM timing system design

A new beam position monitor (BPM) timing system has been designed for the Advanced Photon Source (APS) storage-ring. The old system used beam-derived triggers. The timing system provided a gate to determine which stored bunch would be processed. While this system served the APS well, it was determined that an RF-derived trigger system would reduce unwanted effects such as measured position intensity dependence. The new BPM timing system provides independently settable RF-derived timing triggers for each BPM. The system uses an existing module design to provide RF-derived triggers for each stored bunch in conjunction with a new module design that selects RF-derived triggers and provides independent delays for each BPM within a sector. The system provides the flexibility to trigger on single or multiple bunches per turn and supports arbitrary trigger patterns of up to 400 turns in length. The design and performance of this new system are discussed.

X-ray BPM-based feedback system at the APS storage ring

At the Advanced Photon Source (APS) storage ring, the X-ray beam position monitors (X-BPMs) measure accurate photon position down to the submicron level. This level of stable measurement has been possible due to 1) superior thermal insulation and vibration damping of the X-ray BPM support structure [1], 2) minimal dependence on the bunch pattern and intensity variations, and 3) use of ultrastable preamplifiers and processing electronics. A new X-BPM interface is under development and will be discussed here. This interface will be integrated into the existing rf-based orbit feedback systems. To study preliminary results, an experimental X-BPM orbit feedback set-up was developed and implemented in one of the bending magnet beamlines. The results from this set-up are encouraging. For an operational fill, a typical orbit drift of 30 microns (at X-ray BPMs) has been reduced to less than 5 microns. The fill-to-fill photon orbit reproducibility has been improved from 75 microns to less than 10 microns.