145 research outputs found
Analytical considerations for linear and nonlinear optimization of the TME cells. Application to the CLIC pre-damping rings
The theoretical minimum emittance cells are the optimal configurations for
achieving the absolute minimum emittance, if specific optics constraints are
satisfied at the middle of the cell's dipole. Linear lattice design options
based on an analytical approach for the theoretical minimum emittance cells are
presented in this paper. In particular the parametrization of the quadrupole
strengths and optics functions with respect to the emittance and drift lengths
is derived. A multi-parametric space can be then created with all the cell
parameters, from which one can chose any of them to be optimized. An
application of this approach are finally presented for the linear and
non-linear optimization of the CLIC Pre-damping rings.Comment: Submitted for publication in Physical Review Special Topics -
Accelerators and Beam
Efficient control of accelerator maps
Recently, the Hamiltonian Control Theory was used in [Boreux et al.] to
increase the dynamic aperture of a ring particle accelerator having a localized
thin sextupole magnet. In this letter, these results are extended by proving
that a simplified version of the obtained general control term leads to
significant improvements of the dynamic aperture of the uncontrolled model. In
addition, the dynamics of flat beams based on the same accelerator model can be
significantly improved by a reduced controlled term applied in only 1 degree of
freedom
Luminosity Scans for Beam Diagnostics
A new type of fast luminosity separation scans ("Emittance Scans") was
introduced at the CERN Large Hadron Collider (LHC) in 2015. The scans were
performed systematically in every fill with full-intensity beams in physics
production conditions at the Interaction Point (IP) of the Compact Muon
Solenoid (CMS) experiment. They provide both emittance and closed orbit
measurements at a bunch-by-bunch level. The precise measurement of beam-beam
closed orbit differences allowed a direct, quantitative observation of
long-range beam-beam PACMAN effects, which agrees well with numerical
simulations from an improved version of the TRAIN code
Extracting chromatic properties of electron beams from spectral analysis of turn-by-turn beam position data
A method to estimate linear chromaticity, RMS energy spread, and chromatic
beta-beating, directly from turn-by-turn beam position data in a circular
electron accelerator, is presented. This technique is based on frequency
analysis of a transversely excited beam, in the presence of finite
chromaticity. Due to the turn-by-turn chromatic modulation of the beam's
envelope, betatron sidebands appear around the main frequency of the Fourier
spectra. By determining the amplitude of both sidebands, chromatic properties
of the beam can be estimated. In this paper, analytical derivations justifying
the proposed method are given, along with results from tracking simulations. To
this end, results from practical applications of this technique at the KARA
electron ring are demonstrated
Identification and characterization of high order incoherent space charge driven structure resonances in the CERN Proton Synchrotron
Space charge is typically one of the performance limitations for the
operation of high intensity and high brightness beams in circular accelerators.
In the Proton Synchrotron (PS) at CERN, losses are observed for vertical tunes
above , especially for beams with large space charge tune shift. The
work presented here shows that this behaviour is associated to structure
resonances excited by space charge due to the highly symmetric accelerator
lattice of the PS, typical for first generation alternating gradient
synchrotrons. Experimental studies demonstrate the dependency of the losses on
the beam brightness and the harmonic of the resonance, and simulation studies
reveal the incoherent nature of the resonance. Furthermore, the calculation of
the Resonance Driving Terms (RDT) generated by the space charge potential shows
that the operational working point of the PS is surrounded by multiple space
charge driven incoherent resonances. Finally, measurements and simulations on
both lattice driven and space charge driven resonances illustrate the different
behaviour of the beam loss depending on the source of the resonance excitation
and on the beam brightness
Interplay of Space Charge and Intra-Beam Scattering in the LHC ion injector chain
The ion injectors of the CERN accelerator chain, in particular the Super
Proton Synchrotron (SPS) and the Low Energy Ion Ring (LEIR), operate in a
strong Space Charge (SC) and Intra-Beam Scattering (IBS) regime, which can
degrade beam quality. Optimizing the ion beam performance requires thus to
study the interplay of these two effects in tracking simulations by
incorporating both SC and IBS effects interleaved with lattice non-linearities.
In this respect, the kinetic theory approach of treating IBS effects has been
deployed. A new, modified approach has been introduced using the formalism of
the Bjorken and Mtingwa model and the complete integrals of the second kind for
faster numerical evaluation. This IBS kick is implemented in PyORBIT and
extensive benchmarking cases against analytical models are shown. Results of
combined space charge and intra-beam scattering simulations for the SPS and
LEIR are presented and compared with observations from beam measurements.Comment: 13 pages, 13 figures, to be submitted to Physical Review Accelerators
and Beam
Detecting chaos in particle accelerators through the frequency map analysis method
The motion of beams in particle accelerators is dominated by a plethora of
non-linear effects which can enhance chaotic motion and limit their
performance. The application of advanced non-linear dynamics methods for
detecting and correcting these effects and thereby increasing the region of
beam stability plays an essential role during the accelerator design phase but
also their operation. After describing the nature of non-linear effects and
their impact on performance parameters of different particle accelerator
categories, the theory of non-linear particle motion is outlined. The recent
developments on the methods employed for the analysis of chaotic beam motion
are detailed. In particular, the ability of the frequency map analysis method
to detect chaotic motion and guide the correction of non-linear effects is
demonstrated in particle tracking simulations but also experimental data.Comment: Submitted for publication in Chaos, Focus Issue: Chaos Detection
Methods and Predictabilit
APPLICATION DE LA METHODE D'ANALYSE EN FREQUENCE EN DYNAMIQUE GALACTIQUE
We study the well-known logarithmic galactic potential through the frequency map analysis method of Laskar in order to deepen our knowledge regarding the dynamics of triaxial power-law galactic models. The principal dynamical features of the system are reviewed within the appropriate Hamiltonian frame of reference. The impact of this new approach in galactic dynamics is investigated by applying the method to the axisymmetric version of the logarithmic potential. The reliability of the method is demonstrated via perturbative techniques and numerical transformations in action-angle variables. Comparison with previous studies involving Fourier methods are also given. By means of frequency map analysis, we provide a global vision of the dynamics of the planar potential for various values of the perturbation parameter. The location and extent of the chaotic zones can be easily visualised. All the important resonances are detected with their actual strength, as well as the associated periodic orbits. The method is then applied to the complete threedimensional version of the logarithmic potential. The quasi-periodic approximations furnished by the method permit to clarify the dynamics of the principal types of orbits and their connection with perturbations of integrable cases of the general Hamiltonian. All the fine details of the dynamics associated with the addition of the third degree of freedom are displayed in the complete frequency map, a direct representation of the system's Arnol'd web. The extent of the chaotic zones and the influence of resonant lines are directly visualized in the physical space of the system. This approach reveals many unknown dynamical features of triaxial galactic potentials and gives strong indications that chaos should be an innate characteristic of triaxial configurations. The impact of these results in the construction of self-consistent galactic models are finally discussed.Dans le but de clarifier les aspects dynamiques des modèles galactiques triaxiaux, le potentiel logarithmique est étudié a travers la méthode d'analyse en fréquence. Les caractéristiques dynamiques principales du système sont présentées en utilisant le formalisme hamiltonien approprié. Afin de comparer cette nouvelle approche avec des études précédentes, la méthode est appliquée a la version axisymétrique du potentiel. La précision de la méthode est démontrée a travers des techniques de perturbation et des transformations numériques en variables action-angle. En outre, la construction des applications fréquence pour plusieurs valeurs du paramètre de perturbation permet de fournir une vision globale de la dynamique du potentiel plan. Les zones chaotiques, les résonances importantes ainsi que les orbites périodiques sont détectées. La méthode est appliquée ensuite a la version tridimensionnelle du potentiel logarithmique. Les approximations quasi-périodiques fournies par la méthode permettent de clarifier la dynamique des types d'orbites principales et leur connexion avec des perturbations du hamiltonien général. Tous les détails fins de la dynamique, qui sont associés a l'addition du troisième degré de liberté, sont représentés dans les applications fréquence complètes, des images instantanées du réseau d'Arnold (''Arnol'd web'') du système. Ainsi, nous pouvons visualiser l'étendu des zones chaotiques et l'influence des lignes résonantes dans l'espace physique du système. Cette approche révèle plusieurs caractéristiques dynamiques inconnues des potentiels galactiques triaxiaux et indique que le chaos doit être une caractéristique importante des configurations triaxiales. Nous discutons finalement l'influence de ces résultats sur la construction des modèles galactiques auto-consistants
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