Magnetic Field Seeding by Galactic Winds

The origin of intergalactic magnetic fields is still a mystery and several scenarios have been proposed so far: among them, primordial phase transitions, structure formation shocks and galactic outflows. In this work we investigate how efficiently galactic winds can provide an intense and widespread "seed" magnetisation. This may be used to explain the magnetic fields observed today in clusters of galaxies and in the intergalactic medium (IGM). We use semi-analytic simulations of magnetised galactic winds coupled to high resolution N-body simulations of structure formation to estimate lower and upper limits for the fraction of the IGM which can be magnetised up to a specified level. We find that galactic winds are able to seed a substantial fraction of the cosmic volume with magnetic fields. Most regions affected by winds have magnetic fields in the range -12 < Log B < -8 G, while higher seed fields can be obtained only rarely and in close proximity to wind-blowing galaxies. These seed fields are sufficiently intense for a moderately efficient turbulent dynamo to amplify them to the observed values. The volume filling factor of the magnetised regions strongly depends on the efficiency of winds to load mass from the ambient medium. However, winds never completely fill the whole Universe and pristine gas can be found in cosmic voids and regions unaffected by feedback even at z=0. This means that, in principle, there might be the possibility to probe the existence of primordial magnetic fields in such regions.Comment: 14 pages, 5 figures. Accepted for publications by MNRAS. A high resolution version of the paper is available at http://astronomy.sussex.ac.uk/~sb207/Papers/bb.ps.g

Relativistic formulation of coordinate light time, Doppler and astrometric observables up to the second post-Minkowskian order

Given the extreme accuracy of modern space science, a precise relativistic modeling of observations is required. In particular, it is important to describe properly light propagation through the Solar System. For two decades, several modeling efforts based on the solution of the null geodesic equations have been proposed but they are mainly valid only for the first order Post-Newtonian approximation. However, with the increasing precision of ongoing space missions as Gaia, GAME, BepiColombo, JUNO or JUICE, we know that some corrections up to the second order have to be taken into account for future experiments. We present a procedure to compute the relativistic coordinate time delay, Doppler and astrometric observables avoiding the integration of the null geodesic equation. This is possible using the Time Transfer Function formalism, a powerful tool providing key quantities such as the time of flight of a light signal between two point-events and the tangent vector to its null-geodesic. Indeed we show how to compute the Time Transfer Functions and their derivatives (and thus range, Doppler and astrometric observables) up to the second post-Minkowskian order. We express these quantities as quadratures of some functions that depend only on the metric and its derivatives evaluated along a Minkowskian straight line. This method is particularly well adapted for numerical estimations. As an illustration, we provide explicit expressions in static and spherically symmetric space-time up to second post-Minkowskian order. Then we give the order of magnitude of these corrections for the range/Doppler on the BepiColombo mission and for astrometry in a GAME-like observation.Comment: 22 pages, 5 figures, accepted in Phys. Rev.

ST-HM design section: Strategy and working methods

The design section of the ST-HM group is devoted to realise all studies for new transport and handling equipment to be procured and installed according to the needs of CERN. In year 2002, the design section has gradually passed from strong engagement in few huge projects to a multitude of ‘less expensive’ projects that require a fast solution and procurement for the LHC installation. The future tasks of our section will be feasibility studies of transport and handling manoeuvres as required for the installation of LHC components and the calculation of lifting tools. In addition the procurement of not yet defined items to solve problems that will occur during the LHC installation. This document gives an overview of the organisation of the design section, the projects and will also underline some problems, such as the incompatibility between the urgency of the users and long CERN purchasing procedures, the work overload, the increasing design requirements for handling tools and operations that were originally not foreseen

Frequency shift up to the 2-PM approximation

A lot of fundamental tests of gravitational theories rely on highly precise measurements of the travel time and/or the frequency shift of electromagnetic signals propagating through the gravitational field of the Solar System. In practically all of the previous studies, the explicit expressions of such travel times and frequency shifts as predicted by various metric theories of gravity are derived from an integration of the null geodesic differential equations. However, the solution of the geodesic equations requires heavy calculations when one has to take into account the presence of mass multipoles in the gravitational field or the tidal effects due to the planetary motions, and the calculations become quite complicated in the post-post-Minkowskian approximation. This difficult task can be avoided using the time transfer function's formalism. We present here our last advances in the formulation of the one-way frequency shift using this formalism up to the post-post-Minkowskian approximation.Comment: 4 pages, submitted to proceedings of SF2

Light propagation in the field of a moving axisymmetric body: theory and application to JUNO

Given the extreme accuracy of modern space science, a precise relativistic modeling of observations is required. We use the Time Transfer Functions formalism to study light propagation in the field of uniformly moving axisymmetric bodies, which extends the field of application of previous works. We first present a space-time metric adapted to describe the geometry of an ensemble of uniformly moving bodies. Then, we show that the expression of the Time Transfer Functions in the field of a uniformly moving body can be easily derived from its well-known expression in a stationary field by using a change of variables. We also give a general expression of the Time Transfer Function in the case of an ensemble of arbitrarily moving point masses. This result is given in the form of an integral easily computable numerically. We also provide the derivatives of the Time Transfer Function in this case, which are mandatory to compute Doppler and astrometric observables. We particularize our results in the case of moving axisymmetric bodies. Finally, we apply our results to study the different relativistic contributions to the range and Doppler tracking for the JUNO mission in the Jovian system.Comment: 17 pages, 4 figures, submitted to Phys. Rev. D, some corrections after revie

Transport and handling LHC components: A permanent challenge

The LHC project, collider and experiments, is an assembly of thousands of elements, large or small, heavy or light, fragile or robust. Each element has its own transport requirements that constitute a real challenge to handle. Even simple manoeuvres could lead to difficulties in integration, routing and execution due to the complex environment and confined underground spaces. Examples of typical LHC elements transport and handling will be detailed such as the 16-m long, 34-t heavy, fragile cryomagnets from the surface to the final destination in the tunnel, or the delicate cryogenic cold-boxes down to pits and detector components. This challenge did not only require a lot of imagination but also a close cooperation between all the involved parties, in particular with colleagues from safety, cryogenics, civil engineering, integration and logistics

Ponts roulants du LHC: Lot 3

Cette présentation traitera du lot 3 des ponts roulants "lourds" du LHC, qui est constitué de sept appareils (plus un en option). Ils doivent équiper les zones d'expériences ATLAS, ALICE et la tête de puits du PMI2. La mise en place de ces ponts roulants est prévue pour les années 2002 et 2003. Cinq ponts sont destinés à l'expérience ATLAS, un portique pour l'expérience ALICE et le dernier pont pour la tête de puits du PMI 2 avec un pont en option ne devant servir que dans le hall de montage. La capacité de ces ponts s'étend sur une gamme de 16t à 2x140t et des hauteurs de levage de 6,5 m à 102 m. Les points forts de ces ponts seront la descente des bobines pour l'expérience ATLAS (deux ponts - trois chariots synchronisés) et la descente de 1200 cryodipoles et tous les aimants du LHC dans PMI2

Construction et installation du LHC

L’installation du LHC a pris, en 2002, une nouvelle dimension avec le début des travaux de la machine en parallèle à ses futures expériences. La première phase des travaux pour le LHC a été la mise en place des services généraux électriques et des tuyauteries d’eau de refroidissement dans le secteur 7/8. Les premières lignes cryogéniques (QRL) seront acheminées au mois de juin. Pour les expériences ALICE et LHC B, après les dernières opérations de démontage, les premiers travaux d’installation des futurs détecteurs ont pu commencer. ATLAS a pu également débuter l’installation de son infrastructure au point 1 avec le début des travaux de charpente dans USA 15. Pour CMS au point 5, la réalisation d’une grande partie de son spectaculaire aimant, est l’objet de nombreuses visites. Le montage des autres parties de son détecteur représentant également une large part d’activité sur d’autres sites