Quench Propagation in the Superconducting 6 kA Flexible Busbars of the LHC

Flexible superconducting cables with currents up to 6 kA will be used to power magnets individually in the insertion regions of the LHC. In case of a quench, the currents in these circuits will decay very fast (with time constants of about 200 ms) such that relatively small copper cross sections are sufficient for these busbars. Quench propagation experiments on a prototype cable and corresponding simulations led to a detailed understanding of the quench behavior of these busbars and to recommendations for the design and application of the cable. Simulations of the quench process in a multi-strand conductor led to a detailed understanding of the way current crosses from superconducting to pure copper strands and how this affects the quench propagation velocity. At nominal current (6 kA), the quench propagation velocities are high (10 m/s) and the hot spot temperature increases rapidly. In this situation, timely quench detection and energy extraction (current reduction) are vital to prevent damage of circuit components

Assessing habitat loss, fragmentation and ecological connectivity in Luxembourg to support spatial planning

The increasing global population requires new infrastructure and urban development, and these land use changes have an impact on habitats and their ecological connectivity. To anticipate and minimise these impacts, environmental and urban planners require tools and methods that they can use at early planning stages. This paper investigates and selects landscape ecology techniques that can be used by planners to assess the effects in terms of changes in habitat loss, fragmentation and ecological connectivity due to expected land use changes. The selected techniques were tested in Luxembourg. Twelve landscape metrics, four connectivity indices, and one connectivity model were selected based on their straightforwardness, widespread application, and accessibility. Land cover maps and proposed areas of urban development up to 2030 were used as input data, together with adapted resistance surfaces from previous studies and a matrix of presence/absence for six target species. The combined analysis reveals a trend of increasing habitat fragmentation and loss of habitats, as well as a reduction of ecological connectivity with regard to all the targeted species, and suggests that this trend will likely continue in the near future. The selected landscape metrics, connectivity indices, the connectivity model and the software used to run them makes the abovementioned techniques easy to use by non-experts, and their combination helps to reduce some of the limitations of each individual technique. Both aspects might be useful in order to mainstream the use of landscape ecology techniques in spatial planning processes

Modelling the net environmental and economic impacts of urban nature-based solutions by combining ecosystem services, system dynamics and life cycle thinking: An application to urban forests

Nature-based solutions (NBS) are gaining relevance as sustainable urban actions because of their potential to provide multiple benefits in the form of ecosystem services (ES), and thus mitigate urban challenges. This paper presents an original semi-dynamic modelling framework that simultaneously considers i) ES supply and demand dynamics, ii) negative environmental impacts, externalities, and financial costs derived from NBS, and iii) life cycle NBS impacts beyond the use phase. Compared to other models, it also aims to be valuable for urban planning actions at site level, i.e., for evaluating the net impacts of specific urban NBS projects. To validate the modelling framework, a proof-of-concept model for urban forests is developed and tested for a case study in Madrid (Spain). The modelling framework is split in two interrelated parts: foreground (dynamic modelling) and background (static modelling). In the foreground, the environmental impacts derived from the use phase of an NBS project are quantified considering its spatio-temporal dynamism, by making use of system dynamics. In the background, the environmental impacts derived from the rest of the life cycle phases of the NBS are quantified making use of steady state life cycle impact assessment. The net economic impact of the NBS project, considering both financial values and externalities, is eventually calculated in the background encompassing all the life cycle phases. Results from the case study illustrate how planning, design, and management decisions over the entire life cycle of an urban forest can influence the net environmental and economic performance of this type of NBS. A discussion is provided to inform on how the modelling framework can help moving beyond the state-of-the-art, and how the derived model can be used for sustainability assessments of urban NBS projects

Nexus between nature-based solutions, ecosystem services and urban challenges

Nature-based Solutions (NBS) are increasingly promoted to support sustainable and resilient urban planning. However, design and planning urban NBS targeted at the needs of the local context require knowledge about the causal relationships between NBS, ecosystem services (ES) and urban challenges (UC) This paper aims at contributing to this knowledge, by systematically identifying nexuses (i.e. qualitative links) between UC, ES and NBS, and describing plausible causal relationships. A conceptual UC-ES-NBS criteria framework was built, and used to guide a two-step systematic literature review on current UC and on the supply of ES by urban NBS. This was followed by a non-systematic literature review, which complemented the previous one by unveiling knowledge gaps on the biophysical and social processes and attributes on which specific ES classes depend. The non-systematic review was also used to identify additional NBS. The UC review identified 18 UC and 58 sub-challenges, and illustrated which UC were more studied, according to the type of literature and environmental and socio-economic attributes of urban contexts. The ES review led to the development of an urban NBS classification, and supported the identification of UC-ES and ES-NBS nexuses, which were analysed and classified into four groups of causal relationship. For the nexuses identified as direct plausible causal relationship, the main processes and attributes on which the supply of specific ES depend were pointed out. Relationships between UC, ES, NBS, processes, and attributes were represented in the form of network diagrams. Our results can be used to support urban policies aimed at mainstreaming NBS and as a basis to further understand UC-ES-NBS relationships

Dynamic Beam Based Calibration of Beam Position Monitors

The degree of spin polarization at LEP is strongly dependent on the knowledge of the vertical orbit. Quadrupole magnet alignment and beam position monitor (BPM) offsets are the main source of the orbi t uncertainty. The error of the orbit monitor readings can be largely reduced by calibrating the monitor relative to the adjacent quadrupole. At LEP, 16 BPM offsets can be determined in parallel durin g 40 minutes. The error of the measure offset is about 30mm. During the LEP run 1997, more than 500 measurements were made and used for the optimisation of polarization. The method of dynamic beam bas ed calibration will be explained and the results will be shown

Performance of the 1-m Model of the 6 kA Superconducting Quadrupole for the LHC Insertions

The LHC dispersion suppressors and matching sections will be equipped with individually powered superconducting quadrupoles with an aperture of 56 mm. In order to minimise the cost of the powering circuits, the quadrupole has been designed on the basis of an 8 mm wide NbTi Rutherford-type cable for a nominal current of 5300 A, corresponding to a gradient of 200 T/m at 1.9 K. In order to validate the design options a model magnet program has been launched. In this report we describe the construction features of the first 1-m long magnet, and present its training performance and the results of protection studies

Observation of radiative spin-polarization at 60.6 GeV

Radiative spin-polarization has been used extensively at LEP to accurately measure the beam energy around the Z resonance. As the LEP physics has moved on to the W boson the calibration based on polarization must be extended towards higher beam energies. This is difficult as the depolarizing effects of spin resonances grow rapidly with beam energy. At LEP it has been possible for the first time to measure transverse beam polarization at 60.6 GeV. To allow a build-up of polarization the tunes and the energy were chosen accurately. A low phase advance optics was used and careful orbit correction was carried out using dynamic beam based alignment data. Harmonic spin matching was applied both in a deterministic and a novel semi- empirical way. (11 refs)

The Protection System for the Superconducting Elements of the Large Hadron Collider at CERN

The protection system for the superconducting elements of the Large Hadron Collider (LHC) [1] at the European Laboratory for Particle Physics (CERN), and its associated equipment are presented: quench detectors, cold diodes, quench heaters and related power supplies, extraction resistors and associated current breakers. Features such as radiation resistance, redundancy and required reliability are discussed

Evaluation of the LEP Centre-of-Mass Energy Above the W-Pair Production Threshold

Knowledge of the centre-of-mass energy at LEP2 is of primary importance to set the absolute energy scale for the measurement of the W-boson mass. The beam energy above 80 GeV is derived from continuous measurements of the magnetic bending field by 16 NMR probes situated in a number of the LEP dipoles. The relationship between the fields measured by the probes and the beam energy is calibrated against precise measurements of the average beam energy between 41 and 55 GeV made using the resonant depolarisation technique. The linearity of the relationship is tested by comparing the fields measured by the probes with the total bending field measured by a flux loop. This test results in the largest contribution to the systematic uncertainty. Several further corrections are applied to derive the the centre-of-mass energies at each interaction point. In addition the centre-of-mass energy spread is evaluated. The beam energy has been determined with a precision of 25 MeV for the data taken in 1997, corresponding to a relative precision of 2.7x10^{-4}. This is small in comparison to the present uncertainty on the W mass measurement at LEP. However, the ultimate statistical precision on the W mass with the full LEP2 data sample should be around 25 MeV, and a smaller uncertainty on the beam energy is desirable. Prospects for improvements are outlined.Comment: 24 pages, 10 figures, Latex, epsfig; replaced by version accepted by European Physical Journal

Material Flow Analysis to Evaluate Supply Chain Evolution and Management: An Example Focused on Maritime Pine in the Landes de Gascogne Forest, France

The Landes de Gascogne forest, located in southwestern France, spans nearly 10,000 km2 and consists largely of maritime pine (Pinus pinaster). This forest in unique to Europe because it is almost entirely created and managed by man for specific industries. On the basis of a material flow analysis, we assessed the upstream supply chain of maritime pine from 2013 to 2019, using a cradle-to-gate approach. The assessment is based on data provided by Alliance Forêts Bois, an important stakeholder of the region and leader in the production of forest resources in France. For various reasons, the harvest totals decreased 10% in the last years. We identified a clear orientation to specific industries—in 2019, 45% was used as pulpwood. This is due to the overall design of the current territory, species of tree, and market values of the pulp and paper industry. The current design provides a limited supply of old growth trees, which produce high-quality logs for construction-based products, and are also more resistant to climate variability. A future shift or balance in raw material flows could be a crucial step in protecting the long-term economic viability of the region. This article aims to contribute to new attempts in providing comprehensive views of stocks and flows in the French forest-wood supply chain