J. Fox

Programmable DSP-based multi-bunch feedback—operational experience from six installations

A longitudinal instability control system, originally developed for the PEP-II, DAΦNE and ALS machines has in the last two years been commissioned for use at the PLS and BESSY-II light sources. All of the installations are running identical hardware and use a common software distribution package. This common structure is beneficial in sharing expertise among the labs, and allows rapid commissioning of each new installation based on well-understood diagnostic and operational techniques. While the installations share the common instability control system, there are significant differences in machine dynamics between the various colliders and light sources. These differences require careful specification of the feedback algorithm and system configuration at each installation to achieve good instability control and useful operational margins. This paper highlights some of the operational experience at each installation, using measurements from each facility to illustrate the challenges unique to each machine....

Design of the PEP-II transverse coupled-bunch feedback system

The design of a 250 MHz bandwidth, bunch-by-bunch feedback system for controlling transverse coupled-bunch instabilities in the PEP-II Asymmetric B-Factory is described. Relevant system parameters and specifications are discussed along with the design of key system components. In particular, the design of the front-end receivers, baseband processing electronics, and kickers are presented in some detail.

Operation and performance of the PEP-II prototype longitudinal damping system at the ALS

A modular programmable longitudinal feedback system has been developed as a component of the PEP-II R+D program. This system is based on a family of VME and VXI packaged signal processing functions which implement a general purpose digital feedback controller for accelerators with bunch spacings of 2 ns. A complete PEP-II prototype system has been configured and installed for use at the LBL Advanced Light Source. The system configuration used for tests at the ALS is described and results are presented showing the action of the feedback system. Open and closed loop results showing the detection and calculation of feedback signals from bunch motion are presented and the system is shown to damp coupled-bunch instabilities in the ALS. Use of the system for accelerator diagnostics is illustrated via measurement of grow-damp transients which quantify growth rates without feedback, damping rates with feedback, and identify unstable modes.

Multi-bunch instability diagnostics via digital feedback systems at PEP-II, DA/spl Phi/NE, ALS and SPEAR

Longitudinal feedback systems based on a common programmable DSP architecture have been commissioned at 4 laboratories. In addition to longitudinal feedback and beam diagnostics these flexible systems have been programmed to provide diagnostics for transverse motion. The diagnostic functions are based on transient domain techniques which record the response of every bunch while the feedback system manipulates the beam. Operational experience from 4 installations is illustrated via experimental results from PEP-II, DA/spl Phi/NE, ALS and SPEAR. Modal growth and damping rates for transverse and longitudinal planes are measured via short (20 ms) transient excitations for unstable and stable coupled-bunch modes. Data from steady-state measurements are used to identify unstable modes, noise-driven beam motion, and noise sources. Techniques are illustrated which allow the prediction of instability thresholds from low-current measurements of stable beams. Transverse bunch train grow-damp sequences which measure the time evolution of instabilities along the bunch train are presented and compared to signatures expected from ion and fast ion instabilities.

The lead-liquid argon sampling calorimeter of the SLD detector

Abstract The lead-liquid argon sampling calorimeter of the SLD detector is one of the largest detectors employing cryogenic liquids now in operation. This paper details the design and performance considerations, the mechanical and cryogenic systems, the absorber design and tower segmentation, the data acquisition electronics, and the control systems of the detector. The initial operational performance of the device is discussed. Detailed resolution studies will be presented in a later paper.

VXI based multibunch detector and QPSK modulator for the PEP-II/ALS/DA/spl Phi/NE longitudinal feedback system

The PEP-II/ALS/DA/spl Phi/NE feedback systems are complex systems implemented using analog, digital and microwave circuits. The VXI hardware implementation for the front-end and back-end analog processing modules is presented. The front-end module produces a baseband beam phase signal from pickups using a microwave tone burst generator. The back-end VXI module generates an AM/QPSK modulated signal from a baseband correction signal computed in a digital signal processor. These components are implemented in VXI packages that allow a wide spectrum of system functions including a 120 MHz bandwidth rms detector, reference phase servo, woofer link to the RF control system, standard VXI status/control, and user defined registers. The details of the design and implementation of the VXI modules including performance characteristics are presented.

Prompt bunch by bunch synchrotron oscillation detection via a fast phase measurement

An electronic system which detects synchrotron oscillations of individual bunches with 4-ns separation is presented. The system design and performance are motivated by the requirements of the proposed B factory facility at SLAC (Stanford Linear Accelerator Center). Laboratory results show that the prototype is capable of measuring individual bunch phases with better than 0.5 degree resolution at the 476-MHz RF frequency.<<ETX>>

Beam diagnostics based on time-domain bunch-by-bunch data

A bunch-by-bunch longitudinal feedback system has been used to control coupled-bunch longitudinal motion and study the behavior of the beam at ALS, SPEAR, PEP-II, and DAΦNE. Each of these machines presents unique challenges to feedback control of unstable motion and data analysis. Here we present techniques developed to adapt this feedback system to operating conditions at these accelerators. A diverse array of techniques has been developed to extract information on different aspects of beam behavior from the time-domain data captured by the feedback system. These include measurements of growth and damping rates of coupled-bunch modes, bunch-by-bunch current monitoring, measurements of bunch-by-bunch synchronous phases and longitudinal tunes, and beam noise spectra. A technique is presented which uses the longitudinal feedback system to measure transverse growth and damping rates. Techniques are illustrated with data acquired at all of the four above-mentioned machines.

Computer modelling of bunch-by-bunch feedback for the SLAC B-factory design

A computer model of the storage ring, including the RF system, wake fields, synchrotron radiation loss, and the bunch-by-bunch feedback system, is presented. The feedback system model represents the performance of a fast phase detector front end (including system noise and imperfections), a digital filter used to generate a correction voltage, and a power amplifier and beam kicker system. The combined ring-feedback system model is used to study the feedback system performance required to suppress instabilities and to quantify the dynamics of the system. Results which show the time development of coupled bunch instabilities and the damping action of the feedback system are presented.<<ETX>>

The Liquid Argon Calorimeter system for the SLC Large Detector

The physical packaging and the logical organization of the liquid argon calorimeter (LAC) electronics system for the Stanford Linear Collider Large Detector (SLD) at SLAC are described. This system processes signals from approximately 44000 calorimeter towers and is unusual in that most electronic functions are packed within the detector itself as opposed to an external electronics support rack. The signal path from the towers in the liquid argon through the vacuum to the outside of the detector is explained. The organization of the control logic, analog electronics, power regulation, analog-to-digital conversion circuits, and fiber-optic drivers mounted directly on the detector is described. Redundancy considerations for the electronics and cooling issues are discussed. >