Abstracts Brochure - CERN

WEPCH092
WEPCH093
WEPCH094
28-Jun-06 16:00 - 18:00 WEPCH — Poster Session
for class of piecewise continuous admissible controls and also for case of non-standard control variation, which is
preserving smoothness, are obtained.
Dynamical Aperture Studies for the CERN LHC: Comparison between Statistical Assignment
of Magnetic Field Errors and Actual Measured Field Errors
M. Giovannozzi, S.D. Fartoukh, S.S. Gilardoni, J.-B. Jeanneret, A.M.
Lombardi, Y. Papaphilippou, T. Risselada, F. Schmidt (CERN)
298
It is customary to evaluate the performance
of a circular particle accelerator by computing
the dynamical aperture, i.e., the domain
in phase space where bounded single-parti-
cle motion occurs. In the case of the LHC the dynamical aperture computation is performed by assuming a statistical
distribution of the magnetic field errors of various magnets’ classes: the numerical computations are repeated for a
given set of realisations of the LHC ring. With the progress in the magnet production and allocation of the available
positions in the ring, the statistical approach has to be replaced by the computation of one single configuration,
namely the actual realisation of the machine. Comparisons between the two approaches are presented and discussed
in details.
Parameter Scans and Accuracy Estimates of the Dynamical Aperture of the CERN LHC
Techniques to make use of large distributed
M. Giovannozzi, F. Schmidt (CERN)
computing facilities allow for denser parameter
scans of the dynamical aperture, i.e.,
the domain in phase space where bounded single-particle motion prevails. Moreover, one can also increase the
number of ’seeds’ each of which represents a possible realisation of multipolar components around the machine. In
this paper the dependence of the dynamical aperture on the step size of the grid of initial conditions and on the
number of seeds is studied. Estimates on the accuracy of the dynamic aperture are derived and the definition of an
improved protocol for numerical simulations is presented.
An Early Beam Separation Scheme for the LHC
The high nominal luminosity of the LHC re-
J.-P. Koutchouk, G. Sterbini (CERN)
quires a large number of bunches spaced by
about 7.5 m. To prevent more than one headon
collision in each interaction region, a crossing angle of 0.285 mrad is necessary. A side effect of this crossing
angle is the increase of the effective transverse beam cross-section, thereby decreasing the luminosity by some 16%.
For the LHC upgrade, depending on the focusing scenarios, this loss significantly increases and largely offsets the
potential gain of a stronger focusing. In this paper we analyze a strategy to circumvent this difficulty, based an early
beam separation using small dipoles placed at a few meters from the interaction point, deep inside the detectors.
This allows quasi co-linear head-on collisions at the crossing point only. From the beam dynamics point of view, the
essential constraint is to control the long-range beam-beam interactions in a scenario where the normalized beam
separation is not constant. In this paper the criteria of the analysis and the performance improvement obtained with
the scheme are discussed. The strength of the dipoles is estimated as well as the impact on the detectors structure.