98476250
The Bi-2212 conductor and magnet program at the National High Magnetic Field Laboratory
The NHMFL has had a long running program to develop Bi2Sr2CaCu2Ox (Bi2212) for high field magnets. The recent development of round wire Bi2212 (RW2212) has strengthened the effort to develop solenoid magnets with fields substantially greater than can be achieved with Nb3Sn. The present paper briefly summarizes some of the results obtained at the NHMFL in the past 12 months. It summarizes the talk given by David Larbalestier at WAMSDO on May 24, 2008. Much of the work is ongoing and will be reported in the normal peer reviewed literature in late 2008.
139229583
Tests of HTS insert coils above 30 T
Recently HTS insert coils have been operated in background magnetic fields over 30 T, reaching record values for the central magnetic field. One YBCO double pancake coil generated 2.8 T in a 31 T background for a total of 33.8 T. A Bi-2212 layer wound coil generated 1.1 T in a 31 T background for a total of 32.1 T. Here we report on the test set-up and the obtained results. Introduction •Goal: demonstrate the suitability of HTS conductors > 30 T •Two insert coils are built and tested in a background magnetic field of 31 T. 1) YBCO insert coil with commercial conductor from SuperPower Inc. 2) Bi-2212 coil using commercial φ 1 mm wire from Oxford Instruments, Superconducting Technology (OST). •Coils are wound and tested at the NHMFL in a 31 T resistive magnet with a 39 mm diameter cryostat. •HTS coils were protected with a quench detection system, circuit breakers and a 0.5 Ohm dump resistor units YBCO coil Bi-2212 coil Conductor 4 by 0.1 mm tape φ 1 mm wire Insulation varnish ceramic braid Impregnation none Epoxy VPI Conductor length m 36 66 Self-inductance mH 1.9 2.6 Field constant mT/A 8.7 9.1 Typical Ic A 120 A at 77 K, SF 330 A at 4.2 K, 5T
118289508
A transformative superconducting magnet technology for fields well above 30 T using isotropic round wire multifilament Bi2Sr2CaCu2O8-x conductor
We report here that magnetic fields of almost 34 T, far above the upper 24 T limit of Nb3Sn, can be generated using a multifilament round wire conductor made of the high temperature cuprate superconductor Bi2Sr2CaCu2O8-x (Bi-2212). A remarkable attribute of this Bi-2212 conductor is that it does not exhibit macroscopic texture and contains many high angle grain boundaries but nevertheless attains very high superconducting critical current densities Jc of 2500 A/mm2 at 20 T and 4.2 K. This Bi-2212 conductor does not possess the extreme texture that high Jc coated conductors of REBa2Cu3O7-x (REBCO) require, avoiding also its high aspect ratio, large superconducting anisotropy and the inherent sensitivity to defects of a single filament conductor. Bi-2212 wires can be wound or cabled into almost any type of superconducting magnet and will be especially valuable for very high field NMR magnets beyond the present 1 GHz proton resonance limit of Nb3Sn technology. This demonstration that grain boundary limits to high Jc can be practically overcome suggests the huge value of a renewed focus on grain boundary properties in non-ideal geometries, especially with the goal of translating the lessons of this Bi-2212 conductor into fabrication of multifilament round wire REBCO or Fe-based superconductors.
205409621
Isotropic round-wire multifilament cuprate superconductor for generation of magnetic fields above 30 T.
Magnets are the principal market for superconductors, but making attractive conductors out of the high-temperature cuprate superconductors (HTSs) has proved difficult because of the presence of high-angle grain boundaries that are generally believed to lower the critical current density, J(c). To minimize such grain boundary obstacles, HTS conductors such as REBa2Cu3O(7-x) and (Bi, Pb)2Sr2Ca2Cu3O(10-x) are both made as tapes with a high aspect ratio and a large superconducting anisotropy. Here we report that Bi2Sr2CaCu2O(8-x) (Bi-2212) can be made in the much more desirable isotropic, round-wire, multifilament form that can be wound or cabled into arbitrary geometries and will be especially valuable for high-field NMR magnets beyond the present 1 GHz proton resonance limit of Nb3Sn technology. An appealing attribute of this Bi-2212 conductor is that, being without macroscopic texture, it contains many high-angle grain boundaries but nevertheless attains a very high J(c) of 2,500 A mm(-2) at 20 T and 4.2 K. The large potential of the conductor has been demonstrated by building a small coil that generated almost 2.6 T in a 31 T background field. This demonstration that grain boundary limits to high Jc can be practically overcome underlines the value of a renewed focus on grain boundary properties in non-ideal geometries.
8278234
High Field Magnets With HTS Conductors
Development of high-field magnets using high temperature superconductors (HTS) is a core activity at the NHMFL. Magnet technology based on both YBCO-coated tape conductors and Bi-2212 round wires is being pursued. Two specific projects are underway. The first is a user magnet with a 17 T YBCO coil set which, inside an LTS outsert, will generate a combined field of 32 T. The second is a 7 T Bi2212 demonstration coil set to be operated in a large bore resistive magnet to generate a combined magnetic field of 25 T. Owing to the substantial technological differences of the two conductor types, each project faces different conductor and magnet technology challenges. Two small coils have been tested in a 38-mm cold bore cryostat inserted in a 31 T resistive magnet: a Bi2212 round-wire layer-wound insert coil that generated 1.1 T for a total of 32.1 T and a YBCO double-pancake insert that generated 2.8 T for a total central field of 33.8 T. Four larger layer-wound coils have been manufactured and tested in a 20 T, 186-mm cold bore resistive magnet: a sizeable Bi-2212 coil and three thin large-diameter YBCO coils. The test results are discussed. The current densities and stress levels that these coils tolerate underpin our conviction that >30 T all-superconducting magnets are viable.
16282327
Modeling the Sun's open magnetic flux and the heliospheric current sheet
By coupling a solar surface flux transport model with an extrapolation of the heliospheric field, we simulate the evolution of the Sun's open magnetic flux and the heliospheric current sheet (HCS) based on observational data of sunspot groups since 1976. The results are consistent with measurements of the interplanetary magnetic field near Earth and with the tilt angle of the HCS as derived from extrapolation of the observed solar surface field. This opens the possibility for an improved reconstruction of the Sun's open flux and the HCS into the past on the basis of empirical sunspot data.
55456468
An efficient method for computing the eigenfunctions of the dynamo equation
Aims. We present an elegant method of determining the eigensolutions of the induction and dynamo equations in a fluid embedded in a vacuum. Methods. The magnetic field is expanded in a complete set of functions. The new method is based on the biorthogonality of the adjoint electric current and the vector potential with an inner product defined by a volume integral over the fluid domain. The advantage of this method is that the velocity and the dynamo coefficients of the induction and the dynamo equation do not have to be differentiated and thus even numerically determined tabulated values of the coefficients produce reasonable results. Results. We provide test calculations and compare with published results obtained by the classical treatment based on the biorthogonality of the magnetic field and its adjoint. We especially consider dynamos with mean-field coefficients determined from direct numerical simulations of the geodynamo and compare with initial value calculations and the full MHD simulations.
54178900
Surface flux evolution constraints for flux transport dynamos
The surface flux transport (SFT) model of solar magnetic field s involves empirically well-constrained velocity and magnetic fields. The basic evolution of the Sun’s large-scale surface magnet ic field is well described by this model. The azimuthally aver aged evolution of the SFT model can be compared to the surface evolution of the flux transport dynamo (FTD), and the evolution of the SFT mod el can be used to constrain several near-surface properties of the FTD model. We compared the results of the FTD model with different upper boundary conditions and diffusivity profiles against the results of the SFT model. Among the ingredients of the FTD model, downward pumping of magnetic flux, related to a positive di ffusivity gradient, has a significant e ffect in slowing down the diffusive radial transport of magnetic flux through the solar sur face. Provided the pumping was strong enough to give rise to a downflow of a magnetic Reyno lds number of 5 in the near-surface boundary layer, the FTD using a vertical boundary condition matches the SFT model based on the average velocities above the boundary layer. The FTD model with a potential field were unable to match the SFT results.
119471022
Overview of tan(beta) Determination at a Linear e+e- Collider
The ratio of the vacuum expectation value of the two Higgs doublets, tan(beta), is an important parameter of the general 2-Higgs-Doublet Model (2HDM) and the Minimal Supersymmetric extension of the Standard Model (MSSM). The expected uncertainty on the determination of tan(beta) at a Linear Collider (LC) of at least 500 GeV center-of-mass energy and high luminosity is reviewed based on studies of neutral and charged Higgs boson production.
118609219
Is there a new weakly interacting boson of mass 214 MeV
We consider the existence of the stated X0 (214 MeV) in Σ+ → pμ+μ− decay found by the HyperCP collaboration. We assume that a fundamental spin zero boson X0 coupled to quarks leads to flavor changing s → dX0 process. We estimate the scalar and pseudoscalar coupling constants by considering Σ+ → pX0 and K+ → π+X0 processes, and find that pseudoscalar coupling dominates. We then evaluate the branching ratios for KL → π0π0X0, π+π−X0 and Ω− → Ⅺ−X0 decays. These rates are found to be in the measurable ranges.