L’incontournable absente. Sur la communication dans les manuels de méthode

L’enseignement des méthodes en sciences humaines se traduit éditorialement par un nombre croissant de publications de type « manuels ». Pour qui s’intéresse à l’épistémologie des sciences humaines, ces manuels représentent une véritable scène d’exposition, de cristallisation, et de modélisation des pratiques de recherche. Il s’agit ici d’analyser comment les « discours de la méthode » intègrent et manipulent, à des degrés et selon des modalités diverses, les dimensions communicationnelles inhérentes à toute recherche. Alors qu’on assiste à un mouvement de prise en compte croissant de l’épaisseur de l’interaction communicationnelle entre le chercheur et les autres acteurs sociaux, le discours méthodologique, de par sa vocation, se trouve pris dans une position contradictoire : s’ouvrir à la complexité des enjeux communicationnels de la recherche (caractère ouvert des situations d’interaction, attitudes de relation aux objets, formes matérielles des documents, rhétorique d’exposition, etc.) tout en réaffirmant les principes d’une épistémologie classique qui assimile la scientificité des procédures à l’extériorité du chercheur vis-à-vis de ce qu’il étudie. Ainsi, de moins en moins « incontournable », la communication demeure-t-elle un objet à conjurer plus qu’à intégrer.Teaching the methods used in the social sciences tends to generate an increasing number of publications of the textbook type. For those who are interested in the epistemology of the social sciences, these books offer an arena in which research practices are exhibited, crystallized, and modeled. The aim of this paper is to analyze how discourses on methodology assimilate the communication aspects inherent in any research, at many levels, and according to various modalities. While there is a trend toward taking increasing account of the depth of communicative interactions between researchers and other social players, by its very nature, methodology finds itself in a contradictory position. That is, it must become aware of the communication challenges presented by research (including the open nature of interactive situations, relationships with objects, the material forms of documents, and expository rhetoric) and at the same time reassert the principles of a classical epistemology that compares the scientific character of practices to the exteriority of researchers toward what they study. Thus, although communication is becoming less and less inescapable, it remains an object that must be averted rather than assimilated

Beam Characterization of Linac 4's ISO3

After the second LHC long shutdown, Linac4 will become the new injector for proton beams to CERN's chain of accelerators. It has been commissioned at a maximum beam current of 25 mA, below the initial specification of 40 mA. At present, the beam current delivered by the linac is limited by the pre-injector. Previous investigations have found that this is due to the emittance of the H− beam extracted from the ion source exceeding the acceptance of the RFQ. Detailed measurements of the beam parameters provided by the ion source at a dedicated test stand confirmed these earlier findings. By extending and adjusting the simulation model implemented using IBsimu, an agreement to the measured emittance values was obtained. An analysis of the simulation results shows that the larger-than-expected emittance is a result of aberration at the extraction electrodes. These are due to a plasma meniscus significantly more convex than predicted by the earlier simulation. Three modifications to the extraction gap were proposed to achieve a shift of the plasma meniscus back towards a more concave position. Two of the changes - a shorter extraction gap and a larger bore diameter - result in significant decreases of the emittance as confirmed by experiments

Emittance reconstruction techniques in presence of space charge applied during the Linac4 beam commissioning

The classical emittance reconstruction technique, based on analytic calculations using transfer matrices and beam profile measurements, is reliable only if the emittance is conserved and the space charge forces are negligible in the beamline between the reconstruction and measurement points. The effects of space charge forces prevent this method from giving sound results up to a relativistic beta of about 0.5 and make it inapplicable to the Linac4 commissioning at 50 and 100 MeV. To compensate for this drawback we have developed a dedicated technique, the forward method, which extends the classical method by combining it with an iterative process of multiparticle tracking including space charge forces. The forward method, complemented with a tomographic reconstruction routine, has been applied to transverse and longitudinal emittance reconstruction during the Linac4 beam commissioning. In this paper we describe the reconstruction process and its application during Linac4 beam commissioning

Benchmarking of PATH and RF-Track in the Simulation of Linac4

A benchmarking campaign has been initiated to compare PATH and RF-Track in modelling high-intensity, low-energy hadron beams. The development of extra functionalities in RF-Track was required to handle an unbunched beam from the source and to ease the user interface. The Linac4 RFQ and downstream accelerating structures were adopted as test case scenarios. This paper will give an overview of the results obtained so far and plans for future code development

Redesign of CERN LINAC3 RFQ for Lead 29+

CERN Linac3 is at the heart of the CERN Heavy Ion Facility, providing 4.2 MeV/u ion beams to the Low Energy Ion Ring (LEIR). It mostly accelerates 208Pb29+, though in recent years runs were performed with 40Ar11+ and 129Xe22+, in view of the raising interest of the physics community towards lighter ions experiments. In the framework of the LHC Injectors Upgrade (LIU) project, measurements and beam dynamics simulations showed that a transmission bottleneck of Linac3 is represented by the RFQ. As this accelerator was originally designed for 208Pb25+, the lower beam rigidity of the heavy ions currently in used – and planned to be used – permits a redesign of the RFQ aimed at increasing its transverse acceptance, and thus the transmitted beam current. The methodology adopted and the results of this study are presented.CERN Linac3 is at the start of the CERN Heavy Ion Facility, providing 4.2 MeV/u ion beams to the Low Energy Ion Ring (LEIR). It mostly accelerates $^{208}$Pb$^{29+}$, though in recent years runs were performed with $^{40}$Ar$^{11+}$ and $^{129}$Xe$^{22+}$, in view of the raising interest of the physics community towards lighter ions experiments. In the framework of the LHC Injectors Upgrade (LIU) project, measurements and beam dynamics simulations showed that a transmission bottleneck of Linac3 is represented by the RFQ. As this accelerator was originally designed for $^{208}$Pb$^{25+}$, the lower beam rigidity of the heavy ions currently in use - and planned to be used - permits a redesign of the RFQ optics aimed at increasing its transverse acceptance, and thus the transmitted beam current. The methodology adopted and the results of this study are presented

L'incontournable absente. Sur la communication dans les manuels de méthode

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Linac4 Transverse and Longitudinal Emittance Reconstruction in the Presence of Space Charge

Linac4 is a pulsed, normal-conducting 160 Mev H^{−} linear accelerator presently under construction at CERN. It will replace the present 50 MeV Linac2 as injector of the proton accelerator complex as part of a project to increase the LHC luminosity. The 3 MeV front end, composed of a 45 keV ion source, a Low Energy Beam transport (LEBT), a 352 MHz Radio Frequency Quadrupole (RFQ) at 3 MeV and Medium Energy Beam Transport (MEBT) housing a beam chopper, and the first Drift Tube Linac (DTL) tank at 12 MeV have been commissioned during the first half of 2014. The transverse and longitudinal emittance reconstruction technique in the presence of space charge, that will be used for the next commissioning stages and permanently during the Linac operation, was successfully tested and validated. The reconstruction method and the results obtained at 3 and 12 MeV are presented in this paper

Linac4 Source and Low Energy Experience and Challenges

At the end of Long Shutdown 2 (LS2), in 2020 Linac4 became the new injector of CERN’s proton accelerator complex. The previous version of the Linac4 H⁻ ion source (IS03), produced an operational pulsed peak beam current of 35 mA, resulting in 27 mA after the Radio-Frequency Quadrupole (RFQ). This limited transmission was mainly due to the extracted beam emittance exceeding the acceptance of the RFQ. A new geometry of the Linac4 source extraction electrodes has been developed with the aim of decreasing the extracted beam emittance and increasing the transmission through the RFQ. The new source (IS04) has been studied and thoroughly tested at the Linac4 source test stand. At the start of the 2023 run, the IS04 was installed as operational source in the Linac4 tunnel and is being successfully used for operation with 27 mA peak current after the RFQ. During high-intensity tests, the source, the linac, and the transfer-line to the Proton Synchrotron Booster (PSB) were also tested with a peak beam current of up to 50 mA from the source resulting in 35 mA at the PSB injection. This paper discusses the recent developments, tests, and future plans for the Linac4 H⁻ ion source.At the end of Long Shutdown 2 (LS2), in 2020 Linac4 became the new injector of CERN’s proton accelerator complex. The previous version of the Linac4 H⁻ ion source (IS03), produced an operational pulsed peak beam current of 35 mA, resulting in 27 mA after the Radio-Frequency Quadrupole (RFQ). This limited transmission was mainly due to the extracted beam emittance exceeding the acceptance of the RFQ. A new geometry of the Linac4 source extraction electrodes has been developed with the aim of decreasing the extracted beam emittance and increasing the transmission through the RFQ. The new source (IS04) has been studied and thoroughly tested at the Linac4 source test stand. At the start of the 2023 run, the IS04 was installed as operational source in the Linac4 tunnel and is being successfully used for operation with 27 mA peak current after the RFQ. During high-intensity tests, the source, the linac, and the transfer-line to the Proton Synchrotron Booster (PSB) were also tested with a peak beam current of up to 50 mA from the source resulting in 35 mA at the PSB injection. This paper discusses the recent developments, tests, and future plans for the Linac4 H⁻ ion source