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The Next Linear Collider (NLC) will collide 180-bunch trains of electrons and positrons with bunch spacing of 1.4 ns. The small spot size (σ[sub y] < 3 nm) at the interaction point requires precise control of emittance, which in turn requires the alignment of individual bunches in the train to within a fraction of a micron. Multi-bunch beam position monitors (BPMs) are to determine the bunch-to-bunch misalignment on each machine pulse. High bandwidth kickers will then be programmed to bring the train into better alignment on the next machine cycle. A prototype multi-bunch BPM system with bandwidth (350 MHz) sufficient to distinguish adjacent bunches has been built at SLAC. It is based on 5 G sample/s digitization of analog sum and difference channels. Calibration tone injection and logging of the single bunch impulse response provide the kernel for deconvolution of bunch-by-bunch position from the sum and difference waveforms. These multi-bunch BPMs have been tested in the Accelerator Test Facility at KEK and in the PEP-II ring at SLAC. The results of these measurements are presented in this paper. [ABSTRACT FROM AUTHOR]

Modern logarithmic amplifiers offer wide dynamic range, high bandwidth, good logarithmic conformance, and low cost making them attractive for beam position measurements. A log-ratio beam position monitor has been designed and built at SLAC for use at the PEP-II B-Factory. An integrated circuit logarithmic amplifier from Analog Devices, the AD8307, recovers the envelope of the 476 MHz harmonic of the beam signal. A log BPM board with two logarithmic and one differential amplifier performs the basic function of forming an output voltage proportional to the difference of the logarithms of the signal amplitudes on opposite electrodes. This voltage is approximately linear with beam position. For this application, we have limited the video bandwidth of the log amps to 50 kHz in order to remove fill pattern dependence. The log BPM board has an interface for testing and simulating beam offsets. The log BPMs were developed for a PEP-II ring protection chassis. Here the log BPMs function to identify dangerous orbit excursions. These excursions are signaled to a system, which can dump the beam. Two such chassis serve to protect the PEP-II rings. [ABSTRACT FROM AUTHOR]

The Beam-Position Monitor (BPM) system for the SLAC PEP-II B-Factory has been in operation for over two years. Although the BPM system has met all of its specifications, several problems with the system have been identified and solved. The problems include errors and limitations in both the hardware and software. Solutions of such problems have led to improved performance and reliability. In this paper we will report on this experience. The process of identifying problems is not at an end and we expect continued improvement of the BPM system. [ABSTRACT FROM AUTHOR]

In many modern storage rings, position monitors process beam signals at frequencies above cutoff for propagating modes in the beam duct. This is common in beam ducts with antechambers. Propagating modes introduce fields at the position monitor pickups unrelated to beam position at the monitor, and therefore can cause errors in indicated position. We discuss issues of generation and propagation of these fields, how they couple to position monitor pickups, and steps that can be taken to minimize their effects. We report some experiences with propagating modes affecting position measurements and our experience with lowering the processing frequency of several BPMs, which must operate in wide beam chamber near the interaction point of the PEP-II ring. [ABSTRACT FROM AUTHOR]

In 1996 and 1997 PSI developed the X-ray Detector Test (XDT) Instrument, sponsored by NASA through UAB/CMC. The Instrument contains three sensor subsystems, each using a high sensitivity photomultiplier tube (PMT) as the radiation event detector. One subsystem has the PMT alone; the second has the PMT coupled to a fiberoptic cylinder; and the third has the PMT coupled to a fiberoptic cylinder with a thin phosphor screen. Subsystem electronics sense each radiation pulse, digitize the amplitude, and assign the pulse to a particular amplitude bin. Pulses are accumulated in temporary memory for 60 seconds, and then recorded in permanent memory. The recorded data then are pulse count and pulse amplitude spectral distribution for nearly sequential 60 second intervals throughout the flight. In 1997 NASA, UAB/CMC, and PSI formulated a plan to fly the XDT Experiment on Mir, because the ISS orbit will be nearly the same as the Mir orbit, and the Mir structure is generally similar to the ISS structure. The XDT Instrument was launched on STS-89 in late January 1998, and operated for five days in the SPACEHAB Module while STS-89 was docked with Mir. The XDT Instrument was then transferred to the Priroda capsule on Mir and operated nearly continuously until mid-May, acquiring radiation event data from the three detector subsystems for 119,700 sixty second intervals. The XDT Instrument was returned to Earth on STS-91 in early June 1998. A key result is that all the Mir flight data are available in a very usable electronic format. The data show dramatic increases in particle flux density when Mir passed through the South Atlantic Anomaly. Analyses are underway to quantify the radiation flux density dependence on position in orbit, and the effects of radiation on the fiberoptic and phosphor screen materials. Results are expected in the near future. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]