Anisotropic monoblock model for computing AC loss in partially coupled Roebel cables

When exposed to time-dependent magnetic fields, REBCO Roebel cables generate AC loss resulting from both magnetic hysteresis and induced inter-strand coupling currents. Until now, the AC loss has been computed in a two-dimensional approximation assuming fully coupled or decoupled strands, and a finite inter-strand resistance could be simulated only with three-dimensional models. In this work, we propose a homogenization procedure that reduces the three-dimensional geometry of the Roebel cable to two dimensions, without ignoring connections between the strands. The homogenized cable consists of two parallel 'monoblocks' with an anisotropic resistivity. The proposed model enables computation of AC coupling loss without the need for complex three-dimensional simulations. For experimental validation, a Roebel cable with soldered strands was prepared. The inter-strand resistance was determined by applying a transverse current and measuring the voltage profile. Additionally, the AC magnetization loss of the cable was measured in fields of 1 to 50 mT with frequencies of 1 to 2048 Hz using a calibration-free technique. With the measured inter-strand resistance as input parameter, the monoblock model gives a good estimate for the AC loss, even for conditions in which the coupling loss is dominant

Genes Influencing Circadian Differences in Blood Pressure in Hypertensive Mice

Essential hypertension is a common multifactorial heritable condition in which increased sympathetic outflow from the central nervous system is involved in the elevation in blood pressure (BP), as well as the exaggerated morning surge in BP that is a risk factor for myocardial infarction and stroke in hypertensive patients. The Schlager BPH/2J mouse is a genetic model of hypertension in which increased sympathetic outflow from the hypothalamus has an important etiological role in the elevation of BP. Schlager hypertensive mice exhibit a large variation in BP between the active and inactive periods of the day, and also show a morning surge in BP. To investigate the genes responsible for the circadian variation in BP in hypertension, hypothalamic tissue was collected from BPH/2J and normotensive BPN/3J mice at the ‘peak’ (n = 12) and ‘trough’ (n = 6) of diurnal BP. Using Affymetrix GeneChip® Mouse Gene 1.0 ST Arrays, validation by quantitative real-time PCR and a statistical method that adjusted for clock genes, we identified 212 hypothalamic genes whose expression differed between ‘peak’ and ‘trough’ BP in the hypertensive strain. These included genes with known roles in BP regulation, such as vasopressin, oxytocin and thyrotropin releasing hormone, as well as genes not recognized previously as regulators of BP, including chemokine (C-C motif) ligand 19, hypocretin and zinc finger and BTB domain containing 16. Gene ontology analysis showed an enrichment of terms for inflammatory response, mitochondrial proton-transporting ATP synthase complex, structural constituent of ribosome, amongst others. In conclusion, we have identified genes whose expression differs between the peak and trough of 24-hour circadian BP in BPH/2J mice, pointing to mechanisms responsible for diurnal variation in BP. The findings may assist in the elucidation of the mechanism for the morning surge in BP in essential hypertension

Magnets for a Muon Collider : Needs and Plans

We describe the magnet challenges for a Muon Collider, an exciting option considered for the future of particle physics at the energy frontier. Starting from the comprehensive work performed by the US Muon Accelerator Program, we have reviewed the performance specifications dictated by beam physics and the operating conditions to satisfy the accelerator needs. Among the many magnets that make up a muon collider, we have identified four systems that represent well the envelope of challenges: the target and capture solenoid, the final cooling solenoid, the accelerator dipoles and the collider dipoles. These systems provide focus for the development of novel concepts, largely based on HTS for reasons of performance, cost and sustainability. After giving a consolidated overview of the needs for the magnet systems, we describe here the basic technology options considered, and the plan for design and development activities.Peer reviewe

Synergetic combination of LIMD with CHPD for the production of economical and high performance MgB2 Wires

We propose an economical fabrication concept, the localized internal magnesium diffusion (IMD) method. Instead of using a single magnesium (Mg) rod in the center of a metal sheath tube, we use large-sized Mg particles (20-50 mesh) mixed well with cheap 97% crystalline boron powder to fill the metal sheath tube. After a repeated drawing process, the coarse Mg is elongated along the core wire axis of the metal sheath tube. Textured MgB2 grains are then formed during the sintering process. In the localized IMD process, however, there is still a need to improve the overall density. In order to increase the density of the composite, a modified cold high pressure densification (CHPD) technique has been applied before the reaction. It is found that the critical current density (Jc) of the sample made from large-sized Mg with crystalline boron powder and treated by CHPD is increased significantly, so that it is quite comparable with the Jc values of samples made from expensive small magnesium and nanosized amorphous boron powder. At 4.2 K and 8 T, the Jc value of the wire in this work with the cheapest starting materials reaches 10 000 A/cm2 , which is similar to reported values for samples made by the powder-in-tube and IMD processes with expensive nanosized amorphous boron powder. A possible mechanism is proposed, and the microstructure is analyzed to explain this interesting feature. The main goal of this work is to develop a novel and cost-effective fabrication technique by combining the localized IMD process with CHPD and using cheap crystalline boron powder to manufacture MgB2 superconductor wires with electromagnetic performance superior to that of low-temperature Nb-Ti superconductors. 2002-2011 IEEE

AC losses of roebel cables with striated 2G YBCO strands

We present experimental data on the ac losses in Roebel cables with striated 2G YBCO strands. Electromagnetic measurements by pick-up coils were carried out at different temperatures between 10K and 85K at frequencies between 2Hz and 20kHz in transverse ac fields up to 0.5T. The Roebel cable samples were assembled from laser cut 2G YBCO strands, which consist of striated filaments prepared with laser scribing. Measurements at different temperatures show that the Roebel cables with striated strands have a lower losses by a factor of strand filament number over the whole temperature range. For analysis, a semi-quantitative approach for unstriated Roebel was found to work satisfactorily. However the Striated Roebel cables appears to have a different field penetration from those of the unstriated Roebel. The coupling current among the filaments has a time constant shorter than 0.1 ms and do not appear to increase in the striated Roebel cables, hence insignificant for most magnets related applications.</p