Paper |
Title |
Page |
CT04 |
Bunch Length Measurements in LEP
|
59 |
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- A.J. Burns, H. Schmickler
CERN, Geneva, Switzerland
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For many years a streak camera has been used for
observing the longitudinal distribution of the particles in
any LEP e+ or e- bunch (5-50 ps r.m.s. length) on a turn
by turn basis, using synchrotron light. In 1996, a
comparison made with the longitudinal vertex
distributions of 3 LEP experiments allowed the
identification and elimination of certain systematic errors
in the streak camera measurements. In 1997, a new bunch
length measurement technique was commissioned that
uses the high frequency slope of the bunch power
spectrum from a button pickup. In 1998, this new method
was confronted with measurements from the streak
camera and the LEP experiments. The measurements
made in 1996 and 1998 are presented, with emphasis on
the calibration of the two instrumental methods and their
respective precision and limitations.
|
|
CT10 |
Real Time Display of the Vertical Beam Sizes in LEP Using the BEXE X-Ray Detector and Fast VME Based Computers
|
87 |
|
- R. Jones, A. Manarin, G. Pignard, E. Rossa, H. Schmickler, M. Sillanoli, C. Surback
CERN, Geneva, Switzerland
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Fast X-ray detectors based on CdTe photoconductors
have been installed in LEP since the beginning of its
operation in 1989. The angular divergence of the high
energy photons from the synchrotron radiation (x-rays)
and the narrow spacing of the 64 photoconductors of the
detector allow a good measurement of vertical beam
profiles down to an rms beam size of 300 mm.
This paper presents some specific parameters and
experimental results of an upgrade program in which the
local processing power of the front-end electronics has
been increased by a factor 50. Such a powerful tool has
allowed a real time display of the time evolution of the
vertical beam sizes. An online correlation plot between
the electron and positron beam sizes (turn by turn) is
also displayed.
These online video images are available in the LEP
control room and are used in daily operation for
luminosity optimisation.
|
|
PS02 |
Chromaticity Measurements at HERA-P Using the Head-Tail Technique with Chirp Excitation
|
103 |
|
- M. Wendt, F. Willeke
DESY, Deutsches Elektronen-Synchrotron, Hamburg, Germany
- A. Boudsko
TRIUMF, Vancouver, Canada
- O.R. Jones, H. Schmickler
CERN, Geneva, Switzerland
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Experiments have been performed in the HERA proton ring
(HERA-p) to test a quasi non-destructive method of chromaticity
measurements for protons. The method is based
on the detection of the head-tail phase shift of coherend betatron
oscillations using a broadband beam position pickup
and a commercial fast-frame oscilloscope. Previous experiments
have relied on a single kick for transverse excitation,
whereas the results presented here were carried out
using swept frequency chirp excitation. The tests proved
to be successful, and the method seems to be a good candidate
for chromaticity measurement in new large hadron
accelerators, such as LHC.
|
|
PS12 |
Performance of the new SPS beam position orbit system (MOPOS)
|
126 |
|
- C. Boccard, T. Bogey, J. de Vries, S. Jackson, R. Jones, J.P. Papis, W. Rawnsley, K. Rybaltchenko, H. Schmickler
CERN, Geneva, Switzerland
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The orbit and trajectory measurement system COPOS
of the CERN SPS accelerator has been in operation since
the construction of the machine in 1976. Over the years
the system has been slightly modified in order to follow
the evolving demands of the machine, in particular for its
operation as a p-pbar collider and, since 1991, for the
acceleration of heavy ions.
In 1995 the performance of the system was reviewed
and the following shortcomings were identified:
- lack of turn-by-turn position measurements due to the
1ms integration time of the voltage to frequency
converters used for the analogue to digital conversion (to
be compared with a revolution time of 23 ms),
- ageing effects on the 200 MHz resonating input filters,
which had over the years drifted out of tolerance. As a
consequence the signal to noise ratio, the linearity and
the absolute precision were affected.
- the calibration system based on electromechanical relays
had become very unreliable, such that frequent
calibrations were no longer possible,
- a remote diagnostic for the observation of timing
signals relative to the beam signals was missing.
For the above reasons a large-scale upgrade program
was launched, the results of which are described in the
following sections.
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|
PT05 |
First results on closed-loop tune control in the CERN-SPS
|
165 |
|
- L. Jensen, O.R. Jones, H. Schmickler
CERN, Geneva, Switzerland
|
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This paper presents the first measurements performed
with the SPS Qloop. The emphasis will be laid on the
model used for designing the regulation loop and how
well it fits reality.
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