Stability diagram of colliding beams

The effect of the beam-beam interactions on the stability of impedance mode is discussed. The detuning is evaluated by the means of single particle tracking in arbitrarily complex collision configurations, including lattice non-linearities, and used to numerically evaluate the dispersion integral. This approach also allows the effect of non-Gaussian distributions to be considered. Distributions modified by the action of external noise are discussed.Comment: 5 pages, contribution to the ICFA Mini-Workshop on Beam-Beam Effects in Hadron Colliders, CERN, Geneva, Switzerland, 18-22 Mar 201

Direct Vlasov solvers

In these proceedings we will describe the theory and practical steps required to build Vlasov solvers such as those commonly used to compute coherent instabilities in synchrotrons. Thanks to a Hamiltonian formalism, we will derive a compact and general form of the linearized Vlasov equation, written using Poisson brackets. This in turn will be the basis of a procedure to build Vlasov solvers, applied to the specific example of transverse instabilities arising from beam coupling impedance.Comment: 25 pages, 2 figure

Electromagnetic fields created by a macroparticle in an infinitely long and axisymmetric multilayer beam pipe

This paper aims at giving an as complete and detailed as possible derivation of the six electromagnetic field components created by an offset point charge travelling at any speed in an infinitely long circular multilayer beam pipe. Outcomes from this study are a novel and efficient matrix method for the field matching determination of all the constants involved in the field components, and the generalization to any azimuthal mode together with the final summation on all such modes in the impedance formulas. In particular the multimode direct space-charge impedances (both longitudinal and transverse) are given, as well as the wall impedance to any order of precision. New quadrupolar terms for the transverse wall impedance are found, which look negligible in the ultrarelativistic case but might be of significance for low-energy beams. In principle from this analysis the electromagnetic fields created by any particular source, with a finite transverse shape, can then be computed using convolutions

A posteriori metadata from automated provenance tracking: Integration of AiiDA and TCOD

In order to make results of computational scientific research findable, accessible, interoperable and re-usable, it is necessary to decorate them with standardised metadata. However, there are a number of technical and practical challenges that make this process difficult to achieve in practice. Here the implementation of a protocol is presented to tag crystal structures with their computed properties, without the need of human intervention to curate the data. This protocol leverages the capabilities of AiiDA, an open-source platform to manage and automate scientific computational workflows, and TCOD, an open-access database storing computed materials properties using a well-defined and exhaustive ontology. Based on these, the complete procedure to deposit computed data in the TCOD database is automated. All relevant metadata are extracted from the full provenance information that AiiDA tracks and stores automatically while managing the calculations. Such a protocol also enables reproducibility of scientific data in the field of computational materials science. As a proof of concept, the AiiDA-TCOD interface is used to deposit 170 theoretical structures together with their computed properties and their full provenance graphs, consisting in over 4600 AiiDA nodes

"Moteur... Action !" - Quand la technique motorisée s'invite sur la scène des loisirs, naissent controverses et conflits

International audienceLes conflits et controverses sont des phénomènes fréquents pour les pratiques de loisir dans les espaces naturels, mais ceux liés aux pratiques motorisées tiennent une place particulière, interrogeant notamment notre rapport au monde en ces temps de crise environnementale. Nous tentons dans cet article de mettre au jour les arguments qui s'échangent dans la cadre de la controverse afin, ensuite, de comprendre les raisons d'une telle controverse. Dans un contexte empreint d'incertitudes, les acteurs donnent leur avis et se positionnent, tant sur les aspects environnementaux que sociaux ou économiques. Un autre champ d'affrontement porte sur la vision de la nature et de la place que les moteurs, symboles par excellence de la technique humaine, peuvent y tenir. Les arguments se répondent et s'opposent point à point, offrant une vision relativement stéréotypée de la situation. Les points des vues des acteurs semblent être fortement situés et liés à la position de chacun dans le réseau

Appeal No. 0805: Beck Energy Corp. v. Division of Oil & Gas Resources Management

Chief\u27s Order 2008-74, 2008-75, 2008-81, 2008-82 & 2008-8

Analyser les sports de nature : de l'ordre local au réseau.

Ce chapitre présente deux conceptions de l'analyse organisationnelle, au sens large (Friedberg, 1933 ; Latour, 2006) appliquées aux sports de nature. Il discute de leur pertinence théorique et empirique à partir d'exemples de travaux réalisés grâce à ces deux cadres théoriques. Il conclut en mettant en évidence les liens entre le contexte étudié, la " focale recherchée " et le choix de l'une de ces deux théories

The LHC Transverse Coupled-Bunch Instability

In this thesis, the problem of the transverse coupled-bunch instabilities created by the Large Hadron Collider (LHC) beam-coupling impedance, that can possibly limit the machine operation, is addressed thanks to several new theories and tools. A rather complete vision of the problem is proposed here, going from the calculation of the impedances and wake functions of individual machine elements, to the beam dynamics study. Firstly, new results are obtained in the theory of the beam-coupling impedance for an axisymmetric two-dimensional structure, generalizing Zotter's theories, and a new general theory is derived for the impedance of an infinite flat two-dimensional structure. Then, a new approach has been found to compute the wake functions from such analytically obtained beam-coupling impedances, over-coming limitations that could be met with standard discrete Fourier transform procedures. Those results are then used to obtain an impedance and wake function model of the LHC, based on the (resistive-) wall impedances of various contributors (collimators, beam screens and vacuum pipe) and additional estimations of the geometrical impedance contributions. Finally, the existing code HEADTAIL, which is a macroparticle simulation code for beam dynamics studies with wake fields, is improved to make possible the simulation of multibunch trains, and a spectral analysis technique is found to facilitate the analysis of the output given by this code, giving the complex tune shifts of the unstable modes present in a simulation. All those theories and tools are used to obtain new results concerning the LHC transverse coupled-bunch instabilities, demonstrating the rather small impact on coupled-bunch instabilities of the number of bunches in a train when the bunch spacing is fixed, and the existence of coupled-bunch modes with intrabunch motion which are more critical than their single-bunch counterparts. A full verification of the complete procedure (impedance theories, impedance model and simulation code) is also performed by comparing the simulation results with actual measurements in the LHC, giving a very good agreement at injection energy and a correct order of magnitude at 3.5 TeV/c. In the end, several predictions concerning the beam stability at the future 7 TeV/c operation of the machine are performed in the case of 50 ns spacing (1404 bunches), revealing that the coupled-bunch transverse mode coupling instability threshold is far above the ultimate bunch intensity but about 20% smaller than its single-bunch counterpart. Stability studies with Landau octupoles at their maximum currents reveal that the beam remains stable at nominal intensity with Q' = 2 in both planes, provided the particle transverse distributions are Gaussian. At ultimate intensity with either Q' = 0 or Q' = 2, or at nominal intensity when the chromaticity is zero, the beam happens to be unstable, even with the octupoles at their maximum currents

GENERALIZED FORM FACTORS FOR THE BEAM COUPLING IMPEDANCES IN A FLAT CHAMBER

The exact formalism from B. Zotter to compute beam coupling impedances has been fully developed only in the case of an infinitely long circular beam pipe. For other two dimensional geometries, some form factors are known only in the ultrarelativistic case and under certain assumptions of conductivity and frequency of the pipe material. We present here a new and exact formalism to compute the beam coupling impedances in the case of a collimator-like geometry where the jaws are made of two infinite plates of any linear material. It is shown that the impedances can be computed theoretically without any assumptions on the beam speed, material conductivity or frequency range. The final formula involves coefficients in the form of integrals that can be calculated numerically. This way we obtain new generalized form factors between the circular and the flat chamber cases, which eventually reduce to the so-called Yokoya factors under certain conditions

THE SIX ELECTROMAGNETIC FIELD COMPONENTS AT LOW FREQUENCY IN AN AXISYMMETRIC INFINITELY THICK SINGLE-LAYER RESISTIVE BEAM PIPE

In this study B. Zotter’s formalism is applied to a circular infinitely long beam pipe made of a conductor of infinite thickness where an offset point-charge travels at any given speed. Simple formulae are found for the impedances and electromagnetic fields both at intermediate frequencies (recovering Chao’s results) and in the low frequency regime where the usual classic thick wall impedance formula does not apply anymore due to the large skin depth compared to the pipe radius