Particle physics experiments make use of magnetic fields up to <inline-formula><tex-math notation="LaTeX">4 \,\mathrm{T}</tex-math></inline-formula> to bend electrically charged particles such that ...their charge and momentum can be determined. The particle energy measurement requires a low amount of material, or material that is highly transparent to particles inside the calorimeter volume. The conflict between the small volume of space reserved for a magnet and having a field of several teslas inside the detector is often resolved by using superconducting magnets. Up to now, large particle physics detector magnets have been constructed with low temperature superconductors, but there are clear benefits from using high temperature superconductors in future particle physics detector designs, such as allowing for an elevated operating temperature and the reduced amount of superconductor needed. In addition to the HTS material itself, additional material is needed to support the Lorentz forces, and to temporarily carry the current in case of a quench since these magnets are always one-of-a-kind and they need to operate reliably and without damage in case of a failure scenario. The stabilizer has to be a low-density material for high particle transparency, such as aluminium. Since the density of the superconductor is a factor of 4 higher than the density of aluminium, a reduction of superconducting material also means an improvement of the particle transparency: the density of a material is directly related to its particle transparency. This paper presents a conceptual design for high temperature superconducting detector magnets and a study of the type of aluminium stabilizer used.
Native vegetation across the Brazilian Cerrado is highly heterogeneous and biodiverse and provides important ecosystem services, including carbon and water balance regulation, however, land-use ...changes have been extensive. Conservation and restoration of native vegetation is essential and could be facilitated by detailed landcover maps. Here, across a large case study region in Goiás State, Brazil (1.1 Mha), we produced physiognomy level maps of native vegetation (n = 8) and other landcover types (n = 5). Seven different classification schemes using different combinations of input satellite imagery were used, with a Random Forest classifier and 2-stage approach implemented within Google Earth Engine. Overall classification accuracies ranged from 88.6-92.6% for native and non-native vegetation at the formation level (stage-1), and 70.7-77.9% for native vegetation at the physiognomy level (stage-2), across the seven different classifications schemes. The differences in classification accuracy resulting from varying the input imagery combination and quality control procedures used were small. However, a combination of seasonal Sentinel-1 (C-band synthetic aperture radar) and Sentinel-2 (surface reflectance) imagery resulted in the most accurate classification at a spatial resolution of 20 m. Classification accuracies when using Landsat-8 imagery were marginally lower, but still reasonable. Quality control procedures that account for vegetation burning when selecting vegetation reference data may also improve classification accuracy for some native vegetation types. Detailed landcover maps, produced using freely available satellite imagery and upscalable techniques, will be important tools for understanding vegetation functioning at the landscape scale and for implementing restoration projects.
In the context of EP R&D, CERN is working on conceptual designs for a possible multi-purpose superconducting magnet test beam facility to be used for future detector and electronic device testing. ...The facility may serve as a replacement of the existing M1 or Morpurgo H8 magnets. The new facility is envisioned to serve all the testing requirements for the next generation of high energy physics particle detectors. Two separate concepts are proposed to satisfy the replacement needs. The magnet will take either the form of a split solenoid, allowing dual use as a dipole or solenoid, or a skateboard tilted racetrack design, allowing dipole function. Both designs allow for at least <inline-formula><tex-math notation="LaTeX">1 \,{\mathrm{m}^{\mathrm{3}}}</tex-math></inline-formula> testing volume and a magnetic field up to 4-T. It is envisioned to use Niobium Titanium Rutherford cables with a Nickel-Aluminium stabiliser. The operation temperature will be 4.5 K with two-phase helium cooling. The stray fields are minimised to stay below 12 mT at a distance of 5 m from the central point.
Arc suppression Snubbers offer safety in high energy superconducting magnet systems. Large superconducting magnets may have arcing across their breakers at the moment of slow dump initiation ...resulting from a sudden current redistribution in the powering circuit. The ATLAS Experiment at CERN experiences such arcing with its 7.3 H Toroidal magnet powering circuit. To discharge the magnets, the current is redistributed to a parallel branch called the Run Down Unit (RDU) by means of a breaker. Due to the physical layout and other metallic components in the vicinity, the power supply and RDU branches have undesirable and unavoidable parasitic inductance, causing a voltage spike over the main breakers at the moment of opening. The resulting arcing deteriorates the breaker contacts, resulting in increased operating temperatures and a more frequent need for maintenance. The arc suppression system developed takes the form of an RC Snubber (Resistor-Capacitor). The Snubber offers the current a low-impedance path, thus smoothing out the current redistribution and suppressing the voltage spike. This initial charging period of the capacitors gives the current enough time to overcome the parasitic inductance, therefore allowing the RDU to smoothly ramp up without a sudden voltage spike. To test the concept, a 1/50th scale demonstrator was developed and showed successful results. After the demonstrator, endurance testing of the electrolytic capacitors was performed to ensure no degradation of the charging characteristics for an equivalent of 20 years of operation. The Snubber was manufactured and implemented with successful results on the ATLAS Toroidal powering circuit.
Coexisting vegetation types in tropical landscapes can respond in contrasting ways to rainfall, despite being in the same climatic envelope. Understanding such heterogeneity in vegetation-rainfall ...interactions is key for predicting how ecosystems might respond to future environmental changes. Here we test whether temporal coupling between vegetation greenness and rainfall is a good indicator of ecosystem state in the landscape. For this, we study a well-preserved landscape of the Brazilian Cerrado that is formed by mosaics of contrasting ecosystems, including savannas, dry forests and gallery forests. First, we correlate the time-series of rainfall and vegetation greenness to quantify their coupling for each vegetation type. We then compare vegetation-rainfall coupling with other state variables, such as local-scale vegetation structural and functional traits, as well as differences in environmental conditions in which these vegetation types exist. Coexisting vegetation types are set in contrasting local-scale environmental conditions and have distinct responsiveness to rainfall. Commonly used structural and functional state variables, such as tree cover and tree height, do not depict such marked differences between the vegetation types, particularly for gallery and dry forests. Dry forests have the strongest coupling and decrease their greenness during dry seasons, reflecting vegetation deciduousness on nutrient-richer soils. In contrast, gallery forests increase their greenness during the dry season, when direct radiation peaks, likely due to perennial access to groundwater. Savannas are less responsive to rainfall and have a more stable greenness throughout the year. Our findings suggest that heterogeneity in local abiotic conditions contribute to determining both vegetation distribution and ecosystem states in these tropical savanna landscapes. Changes in these conditions as a result of climate and land-use changes will likely alter the distribution of vegetation types in the future. Our functional metric may thus be useful for assessing future responses of tropical ecosystems to changes in precipitation.
Tropical savannas are known for the fire‐prone ecosystems, yet, riparian evergreen forests are another important landscape feature. These forests usually remain safe from wildfires in the wet ...riparian zones. With global changes, large wildfires are now more frequent in savanna landscapes, exposing riparian forests to unprecedented impact.
In 2017, a large wildfire spread across the Chapada dos Veadeiros National Park, an iconic UNESCO site in central Brazil, raising concerns about its impact on the fire‐sensitive ecosystems. By combining remote sensing analysis of Google Earth images (2003–2019) with detailed field information from 36 sites, we assessed wildfire impacts on riparian forests. For this, we measured the structure of trees, saplings and herbaceous plants, as well as topsoil variables.
Since 2003, all riparian forests had canopy cover above 90%, but after 2017, canopy cover dropped to 20% in some forests, indicating large variation in wildfire damage. A closer look in the field revealed that, on average, the wildfire killed 52% of adult trees and 87% of tree saplings in flooded forests. In non‐flooded forests, impacts on adult trees were negligible, but fire killed 75% of tree saplings. Opportunistic vines and the invasive grass Melinis minutiflora were already present in severely disturbed flooded forests. In all forests, impacts on many ecosystem variables were related to canopy damage, a variable measurable from satellite. Overall, seasonally flooded riparian forests were the most severely impacted, possibly due to the relatively thinner barks of their trees.
Synthesis and applications. Our findings reveal how riparian forests embedded in tropical savanna landscapes are in danger from large wildfires. The destruction of some forests has opened space for new plant species that may propel a shift to an alternative ecosystem state. Riparian forests are habitat of large savanna animals and their loss could affect entire trophic networks. Managing wildfires and invasive grasses locally is probably the best strategy to maintain riparian forests resilient. As wildfire regimes intensify in tropical savanna landscapes, our findings stress the need for an integrated management that considers riparian forests as a vulnerable element of the system.
Our findings reveal how riparian forests embedded in tropical savanna landscapes are in danger from large wildfires. The destruction of some forests has opened space for new plant species that may propel a shift to an alternative ecosystem state. Riparian forests are habitat of large savanna animals and their loss could affect entire trophic networks. Managing wildfires and invasive grasses locally is probably the best strategy to maintain riparian forests resilient. As wildfire regimes intensify in tropical savanna landscapes, our findings stress the need for an integrated management that considers riparian forests as a vulnerable element of the system.
The Compact Muon Solenoid (CMS) is a general purpose detector, designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T ...superconducting solenoid with 6-m-diameter by 12.5-m-length free bore, enclosed inside a 10,000-ton return yoke made of construction steel. The flux return yoke consists of five dodecagonal three-layered barrel wheels and four end-cap disks at each end comprised of steel blocks up to 620 mm thick, which serve as the absorber plates of the muon detection system. To measure the field in and around the steel, a system of 22 flux loops and 82 3-D Hall sensors is installed on the return yoke blocks. A TOSCA 3-D model of the CMS magnet is developed to describe the magnetic field everywhere outside the tracking volume that was measured with the field-mapping machine. The voltages induced in the flux loops by the magnetic flux changing during the CMS magnet standard ramps up and down are measured with six 16-bit DAQ modules. The off-line integration of the induced voltages reconstructs the magnetic flux density in the yoke steel blocks at the operational magnet current of 18.164 kA. The results of the flux loop measurements during the magnet ramps up and down are presented and discussed.
Future detector magnets call for the development of next-generation large-sized Al stabilized Nb-Ti superconducting cables exhibiting high yield strength for coping with the large stress in wide bore ...magnets with peak magnetic fields up to 6 T, while avoiding significant degradation in residual resistivity ratio. Precipitation type alloys obtained by dilute-alloying of high purity Al with suitable additives like Ni, subjected to partial annealing following cold drawing, can feature a yield strength up to 110 MPa at 4.2 K. For the ATLAS central solenoid, a Nb-Ti cable has been plated with a precipitation-type Al-0.1wt%Ni alloy. However, this conductor with a critical current of 20 kA at 5 T, features a cross-section of only 130 mm 2 . Here, a first step in process scale-up to a 60 kA at 5 T class conductor is described. For the first time, a continuous co-extruded Al-0.1wt %Ni stabilized conductor has been produced with a cross-section as large as 700 mm 2 . Sections of the conductor are work hardened in order to increase the mechanical properties of the as-extruded temper. The mechanical and transport characteristics as a function of the amount of work hardening have been assessed by removing samples after every subsequent step.
Measurement of the CMS Magnetic Field Klyukhin, V.I.; Ball, A.; Bergsma, F. ...
IEEE transactions on applied superconductivity,
06/2008, Letnik:
18, Številka:
2
Journal Article
Recenzirano
Odprti dostop
The measurement of the magnetic field in the tracking volume inside the superconducting coil of the Compact Muon Solenoid (CMS) detector under construction at CERN is done with a fieldmapper designed ...and produced at Fermilab. The fieldmapper uses 10 3-D B-sensors (Hall probes) developed at NIKHEF and calibrated at CERN to precision 0.05% for a nominal 4 T field. The precise fieldmapper measurements are done in 33840 points inside a cylinder of 1.724 m radius and 7 m long at central fields of 2, 3, 3.5, 3.8, and 4 T. Three components of the magnetic flux density at the CMS coil maximum excitation and the remanent fields on the steel-air interface after discharge of the coil are measured in check-points with 95 3-D B-sensors located near the magnetic flux return yoke elements. Voltages induced in 22 flux-loops made of 405-turn installed on selected segments of the yoke are sampled online during the entire fast discharge (190 s time-constant) of the CMS coil and integrated offline to provide a measurement of the initial magnetic flux density in steel at the maximum field to an accuracy of a few percent. The results of the measurements made at 4 T are reported and compared with a three-dimensional model of the CMS magnet system calculated with TOSCA.
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