Mechanical Effects of the Nonuniform Current Distribution on HTS Coils for Accelerators Wound With REBCO Roebel Cable

Future high-energy accelerators will need very high magnetic fields in the range of 20 T. The EuCARD-2 WP10 Future Magnets collaboration is aiming at testing HTS-based Roebel cables in an accelerator magnet. The demonstrator should produce around 17 T, when inserted into the 100-mm aperture of Feather-M2 13-T outsert magnet. HTS Roebel cables are assembled from meander-shaped REBCO-coated conductor tapes. In comparison with fair level of uniformity of current distribution in cables made out of round Nb-Ti or Nb3Sn strands, current distribution within the coils wound from Roebel cables is highly nonhomogeneous. It results in nonuniform electromagnetic force distribution over the cable that could damage the very thin REBCO superconducting layer. This paper focuses on the numerical models to describe the effect of the nonhomogeneous current distribution on stress distribution in the demonstrator magnet designed for the EuCARD-2 project. Preliminary results indicate that the impregnation bonding between the cable glass fiber insulation and layer-to-layer insulation plays a significant role in the pressure distribution at the cable edges. The stress levels are safe for Roebel cables. Assuming fully bonded connection at the interface, the stresses around the edges are reduced by a large factor

Unique functions for Notch4 in murine embryonic lymphangiogenesis

Publisher Copyright: © 2021, The Author(s).In mice, embryonic dermal lymphatic development is well understood and used to study gene functions in lymphangiogenesis. Notch signaling is an evolutionarily conserved pathway that modulates cell fate decisions, which has been shown to both inhibit and promote dermal lymphangiogenesis. Here, we demonstrate distinct roles for Notch4 signaling versus canonical Notch signaling in embryonic dermal lymphangiogenesis. Actively growing embryonic dermal lymphatics expressed NOTCH1, NOTCH4, and DLL4 which correlated with Notch activity. In lymphatic endothelial cells (LECs), DLL4 activation of Notch induced a subset of Notch effectors and lymphatic genes, which were distinctly regulated by Notch1 and Notch4 activation. Treatment of LECs with VEGF-A or VEGF-C upregulated Dll4 transcripts and differentially and temporally regulated the expression of Notch1 and Hes/Hey genes. Mice nullizygous for Notch4 had an increase in the closure of the lymphangiogenic fronts which correlated with reduced vessel caliber in the maturing lymphatic plexus at E14.5 and reduced branching at E16.5. Activation of Notch4 suppressed LEC migration in a wounding assay significantly more than Notch1, suggesting a dominant role for Notch4 in regulating LEC migration. Unlike Notch4 nulls, inhibition of canonical Notch signaling by expressing a dominant negative form of MAML1 (DNMAML) in Prox1+ LECs led to increased lymphatic density consistent with an increase in LEC proliferation, described for the loss of LEC Notch1. Moreover, loss of Notch4 did not affect LEC canonical Notch signaling. Thus, we propose that Notch4 signaling and canonical Notch signaling have distinct functions in the coordination of embryonic dermal lymphangiogenesis.Peer reviewe

3-D mechanical modeling of 20 T HTS clover leaf end coils : Good practices and lessons learned

Very high electromagnetic forces are generated in the superconducting coils of high field accelerator magnets. The cables, which are used to wind the coils, can withstand limited pressure levels and strains generated during the powering without degradation. To protect the cables from mechanical damage, reliable prediction of strain and stress inside the coil is paramount for designing suitable support structure of the magnet. This is naturally done before a magnet is built and tested, which emphasizes the need for reliable modeling. Conventionally, the mechanics in superconducting coils are modeled assuming homogenized material properties inside a homogenized coil volume. Using this so-called coil block approach, predicting the actual cable strain or stress inside the homogenized volume is unreliable. In order to predict reliably the stress in the cable, more detailed representation of the modeling domain is needed. This paper presents a workflow to perform a detailed mechanical analysis using finite-element analysis following the envisioned and more detailed approach. As an example, a high field 20 T+ magnet with clover leaf ends is studied, and results are discussed. The results reveal considerable difference between the behavior of modeled homogenized coil blocks and coils where turns are individually considered

ICED - Inductively Coupled Energy Dissipater for Future High-Field Accelerator Magnets

Future high-field accelerator magnets, like the ones foreseen in the design study of the FCC project and for the EuCARD2 "Future Magnets" program, operate with magnetic fields in the range of 16-20 T. For such magnets the energy density is higher than in the accelerator magnets at present in operation, posing a challenge for the quench protection. Traditionally, quench protection has relied on generating large normal zones in the coil by firing quench protection heaters. The increase of the coil internal resistance results in a fast current decay. This paper introduces the Inductively Coupled Energy Dissipater (ICED) system, based on low resistance loops, which are inductively coupled with the coil. These loops greatly accelerate the current decay by rapidly extracting the energy from the coil, thereby lowering its peak temperature. Because of the potential reduction in stabilizer volume within the conductor, ICED may enable higher engineering current densities in the coil than with the protection relying entirely on dissipating the magnet's energy in the windings. The efficiency of ICED as a passive quench protection system is studied in this paper. We present the effect of such protection structure, on the field quality during standard powering of the magnets and on the cryogenic system. We study electromagnetic forces in the loops and mechanically stable geometric locations within the magnet structure. For the proof of the concept, this system has been employed in Feather-M2 dipole demonstrator. We compare our modeling approach to results gained from a cryogenic test

A fast quench protection system for higherature superconducting magnets

For reaching very high magnetic fields in fully superconducting magnets, beyond 16 T for particle accelerators dipoles and beyond 23 T for solenoids, the use of higherature superconductors (HTS) is unavoidable. Due to the high minimum quench energy in HTS these coils are much more difficult to protect against quenches using conventional methods, such as quench heaters or coupling loss induced quench (CLIQ). Although it is possible to use a dump resistor on a short HTS magnet, extracting the energy externally, this does not provide a solution for longer magnets or magnets operated in a string, because the extraction voltage becomes unacceptably high. Here, a method named E3SPreSSO (External Energy Extraction Symbiotic Protection System for Series Operation) is proposed that allows for fast energy extraction in HTS magnets. The E3SPreSSO comprises of units with a near-zero self-inductance superconducting circuit, connected in series with the main magnet. When the protection is triggered, these devices are turned resistive, using quench heaters, overcurrent or CLIQ, causing them to absorb the energy of the system. The units can be located outside the main magnet and do not generate magnetic field. Therefore, it is possible to use relatively cost-efficient and robust Nb-Ti or possibly MgB2 (at higher temperatures). This paper introduces the concept and provides an analytical method weighing the different options for designing the E3SPreSSO units themselves

Layout Study for the Dipole Magnets of the Future Circular Collider Using Nb-Ti and Nb3_{3}Sn

With the Large Hadron Collider (LHC) up and running, studies have started for its successor. Under study is the Future Circular Collider (FCC), which has a circumference of about 100 km, aiming at a proton–proton collision energy of 100 TeV. Consequently, the main bending dipole magnets have to operate at a magnetic field of 16 T. As a first step towards its realization, this paper presents the results of a parametric study of the cross-sectional layout for dipole magnets with a field in the range of 13–17 T using Nb–Ti and Nb_3Sn superconductors. The principal layouts included are the classical Cosine-Theta, the Canted Cosine-Theta, and the Block type. Conductor cost can be reduced significantly when a graded hybrid solution is chosen. Optimizing such complex magnet layouts requires an iterative algorithm, which arranges the positions of the various blocks of coil windings in the coil cross section, thereby finding the thickness of the coil layers. The iterative algorithm is coupled to an adiabatic quench model, which finds an optimal copper-to-superconductor fraction for each of the layers. Outside the iterative cycle, a pattern search algorithm is applied to find a cost optimal distribution of the magnetic field generated by each coil layer

Investigation of REBCO Roebel Cable Irreversible Critical Current Degradation under Transverse Pressure

The Roebel cable utilized in High Field accelerator magnets is subject to high transversal electromagnetic forces. The conductor response to exerted pressure depends from the geometry and materials of the cable. A transverse loading test was performed for an impregnated cable in cryogenic conditions. The test revealed Roebel cable being able to withstand elevated average pressure level common to dipole magnets, when the pressure load is exerted by a stiff press tool. However, the mechanism for irreversible current degradation during the transverse loading during powering remains so far unknown. This paper focuses on finding likely failure mechanisms when a magnet is powered. The cable is wound with a glass-fiber sleeve and impregnated with epoxy. Epoxy has much lower stiffness than the coated conductor. When the cable is subjected to transverse loading, abrupt changes in cable thickness and material properties may lead to irreversible degradation of the conductor. As the tape crosses the epoxy-filled central gap region of the cable, the discontinuous change of the support stiffness generates bending strains and shear stress in the conductor. The cable is mechanically modeled. By modeling, the measured axial strain limit of the conductor is connected to transverse pressure limit of the cable

10 kA joints for HTS roebel cables

Future high temperature superconductor (HTS) high field magnets using multitape HTS cables need 10-kA low-resistance connections. The connections are needed between the poles of the magnets and at the terminals in a wide-operating temperature range, from 1.9-85 K. The EuCARD-WP10 Future Magnets collaboration aims at testing HTS-based Roebel cables in an accelerator magnet. Usually, low temperature superconductor (LTS) cables are jointed inside a relatively short soldered block. Powering tests at CERN have highlighted excess heating of a joint following classical LTS joint design. The HTS Roebel cables are assembled from REBCO-coated conductor tapes in a transposed configuration. Due to this, the tapes surface the cable at an angle with the cable axis. A low-resistance joint requires a sufficiently large interface area for each tape. Within one twist pitch length, each tape is located at the surface of the cable over a relatively small non-constant area. This geometry prevents making a well-controlled joint in a compact length along the cable. This paper presents a compact joint configuration for the Roebel cable overcoming these practical challenges. A new joint called fin-block is designed. The joint resistance is estimated computationally. Finally, the test results as a function of current and temperature are presented

NOTCH Decoys That Selectively Block DLL/NOTCH or JAG/NOTCH Disrupt Angiogenesis by Unique Mechanisms to Inhibit Tumor Growth

A pro-angiogenic role for Jagged-dependent activation of Notch signaling in the endothelium has yet to be described. Using proteins that encoded different NOTCH1 EGF-like repeats, we identified unique regions of DLL-class and JAG-class ligand/receptor interactions, and developed Notch decoys that function as ligand-specific Notch inhibitors. N1(10-24) decoy blocked JAG1/JAG2-mediated NOTCH1 signaling, angiogenic sprouting in vitro and retinal angiogenesis, demonstrating JAG-dependent Notch signal activation promotes angiogenesis. In tumors, N1(10-24) decoy reduced angiogenic sprouting, vessel perfusion, pericyte coverage, and tumor growth. JAG/NOTCH signaling uniquely inhibited expression of anti-angiogenic sVEFGFR-1/sFlt-1. N1(1-13) decoy interfered with DLL1/DLL4-mediated NOTCH1 signaling and caused endothelial hypersprouting in vitro, in retinal angiogenesis and in tumors. Thus, blockade of JAG- or DLL-mediated Notch signaling inhibits angiogenesis by distinct mechanisms. JAG/Notch signaling positively regulates angiogenesis by suppressing sVEGFR-1/sFlt-1 and promoting mural/endothelial cell interactions. Blockade of JAG-class ligands represents a novel, viable therapeutic approach to block tumor angiogenesis and growth