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« Caminante, son tus huellas el camino, y nada mas », Antonio Machado, « Se hace camino al andar... », Chant XXIX, Proverbios y cantarès, Campos de Castilla, 1917. Avant-propos : notre conception de la trace Nous concevons ici la trace, à l’instar du poème d’Antonio Machado, comme un construit chemin faisant, c’est-à-dire dans une tradition ignorante tant du point de vue des sciences de l’information et de la communication que de l’informatique et du traitement automatique des langues. Il ne ...

Avec le xxie siècle, semble émerger un genre nouveau, celui de l’Homme trace. Jamais dans l’histoire de l’humanité, les outils technologiques n’ont été aussi nombreux et aussi efficaces non seulement pour communiquer, mais aussi enregistrer les moindres faits et gestes du quotidien. Il s’ensuit une forme de traçabilité humaine qui suscite les inquiétudes les plus déraisonnables et des questionnements éthiques, légitimes et inédits, qui touchent aux notions mêmes d’intimité et de liberté. Observant et analysant certaines des traces les plus exemplaires de l’homme contemporain, les spécialistes réunis ici placent ces interrogations primordiales en perspective. Dépassant l’illusoire évidence de la « trace », ces chercheurs, issus de champs disciplinaires variés (sciences de la communication, sociologie, informatique, psychologie, linguistique, mais aussi géographie et anthropologie), traitent le sujet sous des angles divers, déconstruisent la notion de trace et en dégagent un nouveau paradigme. Émerge ainsi l’absolue nécessité de mettre en rapport le contexte de production de la trace, celui de sa réception et de son interprétation. Une exploration contemporaine de la nature fondamentale de l’Homme.

International audience; Within the framework of the Horizon 2020 thematic network Inno4Grass (www.inno4grass.eu), 55 ‘practice & science meetings’ have been carried out using a multi-stakeholder, participatory approach, in order to bridge the gap between science and practice and deliver a comprehensive analysis of grassland innovations across eight European countries. Three project phases can be distinguished: (1) common guidelines under discussion, (2) introduction and preliminary test of the guidelines, (3) additional training on the discussion process. A structured feedback on the meetings held was provided by the organisers by means of a questionnaire, including information about duration, preparatory material, participants, discussion methods and evaluation of the meetings by the organisers. This information allows computing of mean values and distribution of the most relevant variables. Only a few of them were affected by the project phase. In particular, there was an increase in the use of farm portraits and of scientific literature over the project phases. All aspects describing the success of meetings were positively assessed. This suggests that the methodology for the conduction of the practice & science meetings within Inno4Grass was already relatively well established at the beginning of the project.

During the 2017 run of the LHC, several applications and tools underwent improvements and new features were added. Next to others, the main focus was on a new system for coupling measurement, based on the ADT AC-Dipole and the luminosity control system, to which e.g. separation and crossing-angle levelling functionality were added. For 2018, it is foreseen to push these systems even further: $\beta ^{*}$ levelling functionality is on its way to be available in the luminosity control system and new approach for precise tune measurements through ADT excitation and pickups is in the planning stage. This paper gives an overview of the relevant improvements done in 2017 and an outlook of what is foreseen to be improved for the 2018 run.

In view of the newly implemented variable Abort Gap Keeper (AGK), this paper will review the protection layers that should prevent an injection of beam into the abort gap and identify the critical regions inside the abort gap. In particular, it will examine the accidental injection of several bunches into the abort gap after a filling-pattern change in September 2017 and discuss the lessons learned.

The steering program YASP was introduced in the LEIR injection as well as the extraction lines in 2016 to correct the trajectories with well-known model based correction algorithms such as MICADO or SVD. In addition a YASP configuration was prepared to correct the extraction line together with the first turn of the PS. In this way the injection oscillations can be corrected while keeping the trajectory reasonable in the PS injection line., CERN Proceedings, Vol 2 (2017): Proceedings of the Injector MD Days 2017

Most of the time, for the daily operation of the LHC, dedicated operational applications are used, and the expert have their own applications to control their equipment, do specific machine developments and studies. In some cases, these expert applications need to adapted. This presentation will demonstrate why this system applications implies a lot of disadvantages. In addition, commons problems and requirements which are easily identified in all groups are shown. Finally it will propose an alternative approach to overcome these issues.

The time spent at injection takes a big share of the LHC global turnaround time. This paper will explain the elements of the injection process and how they contribute to the injection duration, with an attempt to analyse where improvement could be made to increase the injection efficiency.

To minimise the beam losses at the moment of an LHC beam dump the 3 μs long abort gap should contain as few particles as possible. Its population can be minimised by abort gap cleaning using the LHC transverse damper system. The LHC Run 1 experience is briefly recalled; changes foreseen for the LHC Run 2 are presented. They include improvements in the observation of the abort gap population and the mechanism to decide if cleaning is required, changes to the hardware of the transverse dampers to reduce the detrimental effect on the luminosity lifetime and proposed changes to the applied cleaning algorithms.

In 2013, at the end of the LHC physics run I, several quench tests took place with the aim to measure the quench limit of the LHC superconducting magnets. The LHC superconducting magnets in the dispersion suppressor of IR7 are the most exposed to beam losses leaking from the betatron collimation system and represent the main limitation for the halo cleaning. A collimation quench test was performed with 4 TeV proton beams to improve the quench limit estimates, which determine the maximum allowed beam loss rate for a given collimation cleaning. The main goal of the collimation quench test was to try to quench the magnets by increasing losses at the collimators. This note describes the procedure during the test and the first results with the data. Losses of up to 1 MW over a few seconds were generated by blowing up the beam, achieving total losses of about 5.8 MJ. These controlled losses exceeded by a factor 2 the collimation design value, and the magnets did not quench.

The many modifications of the software packages that have been done during LS1 will be reported. Based on the issues and requirements that have been presented in the 2012 Evian workshop [1], the solutions implemented and their impact on operation will be explained, the status of these different upgrade projects will be presented. Without doing a complete inventory of the control room applications, those with important functional modifications or presenting issues will be covered.

The LHC superconducting magnets in the dispersion suppressor of IR7 are the most exposed to beam losses leaking from the betatron collimation system and represent the main limitation for the halo cleaning. In 2013, quench tests were performed at 4 TeV to improve the quench limit estimates, which determine the maximum allowed beam loss rate for a given collimation cleaning. The main goal of the collimation quench test was to try to quench the magnets by increasing losses at the collimators. Losses of up to 1 MW over a few seconds were generated by blowing up the beam, achieving total losses of about 5.8 MJ. These controlled losses exceeded by a factor 2 the collimation design value, and the magnets did not quench., peer-reviewed

Chromatic coupling was regularly measured in the LHC throughout 2012. A first beam-based correction of chromatic coupling was applied during a dedicated MD. In this note we summarise the measurements and results showing a significant reduction in the chromatic coupling for both beams.

The current crossing angle scheme at LHCb interaction point (horizontal crossing angle and vertical beam separation) prohibits the use of the LHCb dipole positive polarity for 25 ns bunch spacing operation since the beam separation at the first parasitic encounter is very small inducing unwanted beam encounters. To overcome this limitation a different crossing angle scheme was proposed in 2007 by W. Herr and Y. Papaphilippou. The new schema implies a vertical external crossing angle that together with the horizontal internal crossing angle, from the LHCb dipole and its three compensator magnets, defines a new tilted crossing and separation plane providing enough beam separation at the parasitic encounters. This paper summarizes the feasibility study of the new crossing scheme, the implementation in routine operation and analyzes the beam stability during the building up of the tilted crossing plane.

The Large Hadron Collider is equipped with 100 movable collimators. The LHC collimator control system is responsible for the accurate synchronization of around 400 axes of motion at the microsecond level, and with the precision of a few micrometers. The status and settings of the collimators can be monitored by three displays in the CERN Control Center, each providing a different viewpoint onto the system and a different level of abstraction, such as the positions in mm or beam size units. Any errors and warnings are also displayed. In this paper, the display operation is described, as well as the interaction that occurs when an operator is required to identify and understand an error in the collimator settings., peer-reviewed

During the night of 12-13 September 2012 the LHC collided protons with lead nuclei for the first time, demonstrating the feasibility of hybrid collisions despite the basic two-in-one magnet design. The centre-of-mass energy was 5 TeV per colliding nucleon pair, "Stable Beams" were declared 9 hours after the first injection of Pb beams in 2012. The integrated luminosity delivered to the four large LHC experiments was sufficient to yield new physics results. Within the same fill, stable beams were declared twice more, with the collision points displaced longitudinally by ±0.5 m from their usual locations. We provide a general overview of this p-Pb pilot physics fill before focusing on beam data at injection energy and at flat-top, before stable beams for physics were declared. We monitored the beam parameters throughout the fill and present an analysis of their evolution based on a simulation of intra-beam scattering (IBS), synchrotron radiation and the consumption of the beam intensity by collisions ("luminosity burn-off"). We also present some considerations on beam-beam effects with unequal beam sizes and the pilot run is compared, in this respect, to expectations for the forthcoming physics run in January. This pilot run was a major step in the preparation of the physics run. However it was not possible to perform an additional feasibility test designed to clarify the limits to the intensity of two beams injected and ramped with unequal revolution frequencies. We describe the plan for this test and discuss the reasons why it could not be carried out.

The first part of the feasibility test of p-Pb operation of the LHC successfully demonstrated the possibility of injecting Pb bunches in the presence of many proton bunches without apparent harmful effects from moving long-range beam-beam encounters. Two bunches in each beam were accelerated to top energy where the RF frequencies of the two rings could be locked together. Finally an RF-rephasing operation to move the collision points some 9 km, back to their proper places succeeded on the first attempt. This note also provides documentation of the many changes made to the LHC operational sequence and interlocking in order to implement this completely new mode of collider operation.

On the 25th of October 2011, a physics fill( Fill nr 2252) was dedicated to providing ATLAS & CMS with high pile-up collisions. A peak pile-up (number of inelastic interactions per crossing) μ of almost 35 was achieved. Part of the test was also to bring the pile-up to values < 0.5 and this was achieved by separating the beams in steps. The Head-On collisions were restored after each IP separation to study its effects. In this note observations of the beam parameters evolution (bunch current, emittances and length) are presented. Some conclusions are drawn and suggestions for future MDs are discussed.

This presentation will give a review from the operations team of the performance and issues of the beam based systems, namely RF, ADT, beam instrumentation, controls and injection systems. For each of these systems, statistics on performance and availability will be presented with the main issues encountered in 2012. The possible improvements for operational efficiency and safety will be discussed, with an attempt to answer the question "Are we ready for the new challenges brought by the 25ns beam and increased energy after LSI? ".

This note highlights the results obtained during the third so-called ATS MD which took place in 2011. The goal of this MD was extremely challenging, targeting a pre-squeezed beta* of 40 cm in ATLAS and CMS, followed by a telescopic squeeze of these two insertions to finally reach a beta* of 10 cm both at IP1 and IP5. Due to the rather poor machine availability during the MD period, the time initially allocated to the ATS studies was hardly cut by a factor of 2, and "only" the achromatic pre-squeeze down to beta*=40 cm was demonstrated with beam.

The objective of the MD was the injection into LHC of batches of nominal intensity bunches at 25 ns spacing, with setting up of the relevant machine systems and first observations of beam characteristics and identification of potential issues. During the test, the beams were setup in the SPS and both transfer lines, and trains of 24 bunches at 25 ns spacing were injected into LHC for both beams. A total of 216b per beam were accumulated (9 injections), limited only by the time available. In this note observations are presented on setting up of the lines, beam losses at injection, beam instrumentation performance, damper, RF capture, vacuum pressures, beam screen temperatures, bunch emittances and lifetimes. Some conclusions are drawn and suggestions for future MD discussed.

In this test we demonstrated that in the absence of strong long range interactions a levelling of the luminosity can be achieved by a small transverse offset.

This note gives a short summary of the MD on transverse coupled-bunch instabilities together with a few pre-liminary results. This MD aimed at giving measurements of the coupled-bunch instability rise times due to the LHC impedance, both at 450 GeV and 3:5 TeV, for a beam with one batch of 36 bunches following a batch of 12 bunches, with 50 ns spacing.

This note describes the results obtained during the first so-called ATS MD where a new injection optics was commissioned and ramped to 3.5 TeV.

This paper reports on the first successful attempt to inject and ramp LHC beams with collision tunes. Using the same tunes throughout the entire LHC cycle has three clear advantages: • Shorter squeeze sequence and hence saving time for luminosity production. • Less complexity in the operation of feed-backs. • Absence of tune swing crossing 7th and 10th order resonances.

Fusion-evaporation in the $^{124}$Sn+$^{136}$Xe system is studied using a high intensity xenon beam provided by the Ganil accelerator and the LISE3 wien filter for the selection of the products. Due to the mass symmetry of the entrance system, the rejection of the beam by the spectrometer was of the order of $5times10^8$. We have thus performed a detailed statistical analysis to estimate random events and to infer the fusion-evaporation cross sections. No signicant decay events were detected and upper limit cross sections of 172 pb, 87 pb and 235 pb were deduced for the synthesis of $^{257}$Rf, $^{258}$Rf and $^{259}$Rf, respectively., Comment: 7 pages, 4 figures

The unprecedented design intensities of the LHC require several important advances in beam collimation. With its more than 100 collimators, acting on various planes and beams, the LHC collimation system is the biggest and most performing such system ever designed and constructed. The solution for LHC collimation is explained, the technical components are introduced and the initial performance is presented. Residual beam leakage from the system is analysed. Measurements and simulations are presented which show that collimation efficiencies of better than 99.97 % have been measured with the 3.5 TeV proton beams of the LHC, in excellent agreement with expectations., peer-reviewed

Une technique originale fondée sur la mesure de temps de réactions nucléaires a été développée au laboratoire du Grand Accélérateur National d'Ions Lourds à Caen (GANIL) pour mettre en évidence l'existence de noyaux d'éléments super-lourds - de masse très supérieure à ce qui existe sur terre à l'état naturel - et pour sonder leur stabilité.

A series of LHC injection tests was performed in August and September 2008. The first saw beam injected into sector 23; the second into sectors 78 and 23; the third into sectors 78-67 and sectors 23-34-45. The fourth, into sectors 23-34-45, was performed the evening before the extended injection test on the 10th September which saw both beams brought around the full circumference of the LHC. The tests enabled the testing and debugging of a number of critical control and hardware systems; testing and validation of instrumentation with beam for the first time; deployment, and validation of a number of measurement procedures. Beam based measurements revealed a number of machine configuration issues that were rapidly resolved. The tests were undoubtedly an essential precursor to the successful start of LHC beam commissioning. This paper provides an outline of preparation for the tests, the machine configuration and summarizes the measurements made and individual system performance.

The commissioning of CERN's ion injector complex [1] to allow 1.1 PeV collisions of ions in LHC is well under way. After the Low Energy Ion Ring (LEIR) in 2005 [2] and the Proton Synchrotron (PS) in 2006 [3], the Super Proton Synchrotron (SPS) has now been commissioned with the 'Early' ion beam, which should give a luminosity of $5×10^{25}cm^{-2}s^{-1}$ in the LHC. This paper summarizes the operation in 2007 of all the machines involved in the ion injection chain.

A well matched injection in the SPS is very important for preserving the emittance of the LHC beam. The paper presents the algorithms used for the analysis and the results of the optics measurements done in the transfer line TT2-TT10 and in the SPS. The dispersion is computed by varying the beam momentum and recording the offsets at the BPMs, while the Twiss parameters and emittance measurements in TT2-TT10 are performed with beam profile monitors equipped with OTR screens. These results are completed by those obtained with a matching monitor installed in the SPS as a prototype for the LHC. This device makes use of an OTR screen and a fast acquisition system, to get the turn by turn beam profiles right at injection in the ring, from which the beam mismatch is computed and compared with the results obtained in the line. Finally, on the basis of such measurements, a betatron and dispersion matching of TT2-TT10 for injection in the SPS has been performed and successfully put in operation.

Good control of key parameters like dipole field, tune and chromaticity is a basic requirement for fast cycle commissioning and for good beam transmission through the SPS ramp. The reproducibility of those parameters depends on power converter tracking, eddy currents and remnant fields. The new SPS control system was used to study some of the problems in the low energy ramp segment of the fixed target beam. A small modification of the function generation for the main converters is shown to reduce residual converter tracking errors by more than one order of magnitude. Tune and chromaticity corrections have been analyzed and summarized for different cycles, both for the ramp as well for the injection plateau where eddy current may play a significant role.

The values of the betatron tunes (i.e. the working point) of a circular accelerator are a key feature for the machine operation. This report presents systematic studies, carried out in the SPS, aimed at assessing the single particle beam behaviour as a function of the working point, close to the SPS working point for the LHC beam (Qh=26.13, Qv=26.18). A dynamic scan of the horizontal and vertical tunes during the SPS MD segment allowed us to determine the amplitude of the integer resonance stop-band. Transverse beam emittance evolution, beam losses and resonant driving terms were considered as parameters characterizing the different working points. The measurements were performed with the LHC pilot bunch circulating at constant momentum p=26 GeV/c. The description of the measurement setup will be followed by the discussion of the results. Finally we will propose possible improvements for future studies of the same type.

MAD-X is CERN's successor for MAD8, a program for accelerator design with a long history. MAD-X is a modular, better maintainable re-write of MAD8 with data structures written in `C'. Early on in the design of MAD-X we relied on the fact that older or doubtful modules could be replaced by new modules using the PTC code by E. Forest. Both codes remain independent entities but are linked via a converter to the MAD-X data structures. PTC is used for symplectic tracking of smaller machines and transfer line using better defined physical models of the elements and taking into account of how the elements are placed in the tunnel. The matching of the LHC will profit form the fact that the high order nonlinear parameters are provided by a PTC Normal Form analysis.

This high level control software used in the tests of TT40 and TI8 in 2003 and 2004 was developed by the LSA project team. This note describes the tools used, the architecture of the system and the functionality of the software provided. The architecture chosen and validated by the tests will be used for the LHC high level control software. Future developments are discussed.

The dispersion measurement is indispensable to minimize the dispersion mismatch, which can be a major source of blow-up for the LHC beam in the SPS at injection. An application has been developed to minimize the measurement time and to ease the analysis. This paper describes the principle of the dispersion measurement and the application.