Abstracts Brochure - CERN

TUPLS — Poster Session 27-Jun-06 16:00 - 18:00
Calibration Measurements of the LHC Beam Dumping System Extraction Kicker Magnets
The LHC beam dumping system must protect
the LHC machine from damage by reliably
and safely extracting and absorbing the
circulating beams when requested. Two sets
J.A. Uythoven, F. Castronuovo, L. Ducimetière, B. Goddard, G.
Gräwer, L. Pereira, E. Vossenberg (CERN)
of 15 extraction kicker magnets form the main active part of this system. They have been produced, tested and
calibrated by measuring the integrated magnetic field and the magnet current at different beam energies. The calibration
data have been analysed, and the critical parameters are compared with the specifications. Implications for
the configuration, control and operation of the beam dumping system are discussed.
Characterization of Crystals for Steering of Protons through Channelling in Hadronic Accelerators
Channeling of relativistic particles through a
crystal may be useful for many applications
in accelerators, and particularly for collimation
in hadronic colliders. Efficiency proved
to be dependent on the state of the crystal
surface and hence on the method used for
V. Guidi, A. Antonini, G. Martinelli, E. Milan, A. Ronzoni (UNIFE)
V.M. Biryukov, Y.A. Chesnokov (IHEP Protvino) E. Boscolo Marchi,
G. Della Mea, A. Vomiero (INFN/LNL) A. Carnera, A. Sambo (Univ.
degli Studi di Padova) Yu.M. Ivanov (PNPI) W. Scandale (CERN)
preparation. We investigated the morphology and structure of the surface of the samples that have been used in
accelerators with high efficiency. We found that crystal fabrication by only mechanical methods (dicing, lapping, and
others) leads to a superficial damaged layer, which is correlated to performance limitation in accelerators. A planar
chemical etching was studied and applied in order to remove the superficial damaged layer. RBS analysis with lowenergy
protons highlighted better crystal perfection at surface, as a result of the etching. Finally, measurement with
70-GeV protons at IHEP demonstrated a superior performance of the chemically cleaned crystals with respect to
conventional samples. A protocol for preparation and characterization of crystal for channelling has been developed,
which may be of interest for reliable operation with crystals in accelerators.
Optics Study for a Possible Crystal-based Collimation System for the LHC
The use of bent crystals as primary collimators
has been long proposed as an option to R.W. Assmann, S. Redaelli, W. Scandale (CERN)
improve the cleaning efficiency of the LHC
betatron and momentum collimation systems. These systems are presently based on two-stage collimation with
amorphous scatterers and absorbers. Crystals are expected to help by channeling and extracting the halo particles
with large angles, resulting in higher cleaning efficiency. Independent of ongoing studies for crystal qualifications
(not reported here), it is important to understand the required deflection angles and the possible locations of absorbers
for the LHC layout. Optics studies have been performed in order to specify the required angles for various LHC
beam energies and possible locations of absorbers for the deflected halo beam. A possible layout for crystal-assisted
collimation at the LHC is discussed, aiming for a solution which would not change the LHC layout but would make
use of the existing collimator location.
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