Bergoz MX-BPM, Руководство пользователя

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Annex III
Pre print of a contribution to the 1996 Beam Instrumentation Workshop (May 6 - 9, 1996)
Argonne National Laboratory, Argonne, Illinois USA
New Generation Electronics
Applied to Beam Position Monitors
Klaus B. Unser
BERGOZ Precision Beam Instrumentation
F-01170 Crozet, FRANCE
Abstract: Cellular telephones and GPS (Global Positioning System) satellite receivers
are examples of modern rf engineering. Taking some inspiration from those designs, a
precision signal processor module for beam position monitors was developed. It features a
heterodyne receiver (100 MHz to 1 GHz) with more than 90 dB dynamic range. Four
multiplexed input channels are able to resolve signal differences lower than 0.0005 dB with
good long term stability. This corresponds to sub micron resolution when used with a
beam position pick-up with 40 mm free aperture. The paper concentrates on circuit design
and modern dynamic testing methods, used first during development and later for production
tests. The frequency synthesizer of the local oscillator, the phase locked synchronous
detector and the low noise preamplifier with automatic gain control are discussed. Other
topics are design for immunity to electromagnetic interference to ensure reliable operation
in an accelerator environment.
Introduction
Beam position monitors (BPM) are essential diagnostic instruments in a particle
accelerator and every accelerator project usually includes the development of a specific
beam position monitoring system. Conventional beam positions pick-ups use 2 or 4
electrodes (directional couplers or buttons) as position sensors. Beam position is a
function of the amplitude difference of these electrode's signals. The fundamental
frequencies are specific to each particular accelerator and the power spectrum may extend
to many GHz. Many methods for processing the beam position pick-ups signals have
been used or proposed in the past
(1). Modern circular machines and storage rings, for
example synchrotron light sources, have very high demands on the precision of these
measurements. The objective is now to measure beam position with a resolution better
than 1 µm. This requires measurement of the ratio of 4 electrical signals with a precision
better than 0.0005 dB. The amplitude of the signals themselves could change over a range
of more than three decades (>60 dB) for different operating modes.
A universal BPM signal processor
We have taken the initiative to develop a universal BPM signal processor that
would adapt easily to the frequency patterns of different accelerators. Starting point was a
new BPM system designed by J. Hinkson (2), which is optimized t measure
the average
closed orbit position with high resolution. His primary