Test Station for Magnetization Measurements on Large Quantities of Superconducting Strands

In the superconducting main magnets of the Large Hadron Collider (LHC), persistent currents in the superconductor determine the field quality at injection field. For this reason it is necessary to check the magnetization of the cable strands during their production. During four years, this requires measurements of the width of the strand magnetization hysteresis loop at 0.5 T, 1.9 K, at a rate of up to eight samples per day. This paper describes the design, construction and the first results of a magnetization test station built for this purpose. The samples are cooled in a cryostat, with a 2-m long elliptic tail. This tail is inserted in a normal conducting dipole magnet with a field between ± 1.5 T. Racetrack pick-up coils, integrated in the cryostat, detect the voltage due to flux change, which is then integrated numerically. The sample holder can contain eight strand samples, each 20 cm long. The test station operates in two modes: either the sample is fixed while the external field is changed, or the sample is moved while the field remains constant. First results of calibration measurements with nickel and niobium are reported

Development of a Displacement Sensor for the CERN-LHC Superconducting Cryodipoles

One of the main challenges of the Large Hadron Collider (LHC), the particle accelerator under construction at CERN (the European Organization for Nuclear Research) in Geneva, resides in the design and production of the superconducting dipoles used to steer the particles around a 27 km underground tunnel. These so-called cryodipoles are composed of an evacuated cryostat and a cold mass, that contains the particle tubes and the superconducting dipole magnet and is cooled by super uid Helium at 1.9 K. The particle beam must be centred within the dipole magnetic field with a sub-millimetre accuracy, this requires in turn that the relative displacements between the cryostat and the cold mass must be monitored with accuracy. Because of the extreme environmental conditions (the displacement measurements must be made in vacuum and between two points at a temperature difference of about 300 degrees) no adequate existing monitoring system was found for this application. It was therefore decided to develop an optical sensor suitable for this application. This contribution describes the development of this novel sensor and the first measurements performed on the LHC cryodipoles

Optical In-Situ Measurement of Relative Deformations of the LHC Main Dipole Cold Masses

The LHC cryodipoles are composed of an evacuated cryostat and a cold mass, which is cooled by superfluid helium at 1.9 K. To obey constraints imposed by beam dynamics the particle beams must be centered within the mechanical axis of the dipole with a sub-millimeter accuracy. This requires in turn that the relative displacements between the cryostat and the cold mass must be monitored with accuracy at all times. Because of the extreme environmental conditions (the displacement must be measured in vacuum and between two points at a temperature difference of about 300 degrees), no adequate existing monitoring system was found for this application. We describe here a novel optical sensor developed for our scope and we present results of measurements made during the cold test of the dipoles

A Novel Device for the Measurement of the Mechanical and Magnetic Axes of Superconducting Magnet Assemblies for Accelerators

In the context of the LHC superconducting magnet production, especially for dipoles and quadrupoles due to their complexity, it is foreseen to perform acceptance tests, at an early production stage, to detect possible significant deviations from the design values. The knowledge of the magnetic field geometry is very important, especially for the main magnets. In order to get this information a new device has been conceived that measures the magnets at room temperature during different stages of construction. This device incorporates a sensitive measuring probe and an efficient data acquisition system because the coils are only powered at about 10-5 of the nominal D.C. current. It is dedicated to Quadrupole and Dipole (by using Quadrupole-Configured Dipole (QCD) transformation) magnets, but is also easily adaptable to higher order magnets (n = 3, 4 and 5) by specific orientation of the search coils. It is equipped with magnetic sensors (4 fixed tangential coils and AC excitation current for the magnet) and position sensors (3D-laser tracker and light reflector) that allow the simultaneous detection of the magnetic field axis and the cold bore axis. It is equipped as well with a set of 4 LEDs and associated with a CCD camera that allows both the measurement of the cold bore diameter and its position with respect to the mole. This paper describes the system and reports the first results measured on the pre-series magnets recently assembled

Experience with the Fabrication and Testing of the Sextupole Superconducting Corrector Magnets for the LHC

The LHC main dipoles will be equipped with sextupole corrector magnets with a field strength of 1700 x2 (T,m) and a magnetic length of 110 mm to correct sextupole field errors. Within the LHC magnet programme CERN has developed in collaboration with CAT a cosine-q type of design where much emphasis has been put on the cost reduction. The magnet features a two-layer racetrack coil, without end spacers, wound from a rectangular NbTi-wire. The two layers are wound simultaneously turning in opposite directions. The yoke is made of a scissor-type of lamination, which allows bringing the iron close to the coil for field enhancement. In this paper we review the manufacturing experiences with the first 12 prototypes built at CERN and CAT. The results of the training at 4.2 K and 1.9 K are presented along with the magnetic field quality measured at room temperature and at 1.9 K

Stigma Management Strategies of Autistic Social Media Users

Background: Research on stigma management strategies in autism relies on questionnaires or experiments, leading to a gap in understanding of how to identify the strategies in naturalistic interactions. The identification of individual (adapting minority group characteristics) and collective (positively redeveloping the in-group) stigma management strategies in online communication is important for understanding how to improve the quality of social media experiences for autistic users. Methods: Using linguistic analysis and engaging with ethnographic perspectives on relationship management, this article develops a novel approach to the identification of individual and collective stigma management strategies of autistic social media users. We combine online observation and interviews with 34 autistic social media users with a corpus-assisted analysis of their posts, divided into two groups according to regular or limited mentions of autism. Results: We show that posts in the first group focus on information provision and exchange and include markers of shared understanding and community building as part of a collective strategy. Interviews with the authors reveal a strong sense of autistic identity and highlight the importance of staying true to one's specific communicative preferences. Posts in the second group are characterized by tentative language (e.g., “seem” and “not sure”) as a way of avoiding social threats by users who report uncertainty and anxiety about misinterpretation of their messages. Conclusions: We show that autistic social media users have specific preferences in how they communicate and express connection online. However, due to negative experiences of social interactions some do not follow these preferences and instead select linguistic and visual resources that can reduce perceived risks of misunderstanding. We question the claims that the internet is inherently enabling for autistic users and call for further research and policy effort to ensure autistic sociality rights in all digital environments. Community brief Why is this an important issue? Autistic people often change their behavior to fit in with nonautistic social environment (thereby “camouflaging” their differences), in person and online. The internet is also a place where autistic people interact with each other and build community. However, research on these online behaviors is mostly focused on conscious actions people can recall when answering survey questions. What was the purpose of this study, and what did the researchers do? We wanted to find out whether it is possible to identify both community building strategies and camouflaging from the language used on social media, as some behaviors may happen without people realizing it. This article uses a method called digital linguistic ethnography to study how 34 autistic adult social media users managed the way they are seen online. The method involved observing where and how participants posted messages and comparing the frequency of word use between participants who regularly mentioned autism in their posts and those who did not. We also interviewed participants about their social media experiences and motivations. What were the results of the study? The results show that participants who mentioned autism used language in specific ways to raise awareness and connect with others. Participants who did not mention autism used more tentative language (e.g., “might,” “seem,” and “not sure”) and worried about being misunderstood. What do these findings add to what was already known? The findings are important as they show that autistic people have specific preferences in how they communicate and express connection on social media. The findings also show that some autistic adults may feel unable to follow these preferences when interacting online, which contradicts previous assumptions that autistic people do not need to mask in online environments. What are the potential weaknesses of the study? Although our participants exhibited a range of internet skills, they may represent a subgroup that is particularly inclined toward social media usage and interaction. This means that our findings may not apply for autistic adults with learning difficulties, for example. Our sample also includes only speaking individuals without the history of intellectual disabilities, which means that that the experiences of nonspeaking autistic people are not represented. How will these findings help autistic adults now or in the future? The findings inform our understanding of what kinds of social media situations make autistic people feel like they fit in or feel uncomfortable. This is important for designing online environments that are inclusive of autistic communicative preferences and have the potential to improve the quality of online social experiences for autistic people

Twin Rotating Coils for Cold Magnetic Measurements of 15 m Long LHC Dipoles

We describe here a new harmonic coil system for the field measurement of the superconducting, twin aperture LHC dipoles and the associated corrector magnets. Besides field measurements the system can be used as an antenna to localize the quench origin. The main component is a 16 m long rotating shaft, made up of 13 ceramic segments, each carrying two tangential coils plus a central radial coil, all working in parallel. The segments are connected with flexible Ti-alloy bellows, allowing the piecewise straight shaft to follow the curvature of the dipole while maintaining high torsional rigidity. At each interconnection the structure is supported by rollers and ball bearings, necessary for the axial movement for installation and for the rotation of the coil during measurement. Two such shafts are simultaneously driven by a twin-rotating unit, thus measuring both apertures of a dipole at the same time. This arrangement allows very short measurement times (typically 10 s) and is essential to perform cold magnetic measurements of all dipoles. The coil surface and direction are calibrated using a reference dipole. In this paper we describe the twin rotating coil system and its calibration facility, and we give the typical resolution and accuracy achieved with the first commissioned unit

The energy calibration of LEP in the 1993 scan

This report summarizes the procedure for providing the absolute energy calibration of the LEP beams during the energy scan in 1993. The average beam energy around the LEP ring was measured in 25 calibrations with the resonant depolarization technique. The time variation of this average beam energy is well described by a model of the accelerator based on monitored quantities. The absolute calibration of the centre of mass energies of the off-peak points is determined with a precision of 2 parts in 10(5) resulting in a systematic error on the Z-mass of about 1.4 MeV and on the Z-width of about 1.5 MeV