7 research outputs found

    The use of a winding model instead of effective continuum model can lead to a drastic reduction of MQE in superconducting coils

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    Thermal stability is an essential parameter for coil design. Previous measurements in an MgB2 solenoid have revealed a change in trend in the minimum quench energy (MQE) dependence on j = I/I., showing lower values than expected for operative current close to the critical current (j ~ 0.90). The obtained MQE is comparable to the one predicted by analytical models in a single tape (1D) being of the order of 1-10 mJ, which indicates that propagation across winding and layers (3D) is not taking place. This reduction of MQE is not obtained in the effective continuum model, because the different turns and layers are not reproduced. Obtaining 1D propagation depends on the ratio between the thermal conductivity of the conductor and insulation and on the cooling conditions at the boundary layers. A numerical model of a superconducting solenoid with full representation of the winding is used to study MQE as a function ofj (0.6-0.99). The quench is triggered applying heat pulses of 40 ms in a region of 4 mm of the outer layer of the coil. The effect of changing the cooling boundary conditions of the coil from adiabatic to isothermal is also investigated

    Influence of the internal architecture of MgB2 conductors in the load line of magnet coils

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    MgB2 conductors have a multifilamentary superconducting structure encased in sheaths of different materials. Conductors with ferromagnetic sheaths, such as Ni or Fe, redistribute the magnetic field, which can affect the critical current of the superconducting filaments. The internal magnetic field distribution inside the conductor is not considered in general when modeling magnets, where the winding is considered as a bulk. The previous assumption can lead to discrepancies between the experimental results and numerical Ic predictions. Hence, a correct analysis of the effects of the ferromagnetic matrix in conductors will lead to savings in cost and weight of the coil design. In this work, the magnetic field distribution inside tapes with different architectures based on existing MgB2 tapes has been obtained. The magnetic field in the filaments is modeled focusing on the influence of the ferromagnetic matrix in the field distribution. The study is extended to round pancake coils based on the prototype coils aimed for its application in wind turbines in the SUPRAPOWER project

    Highly efficient 110-W closed-cycle cryogenically cooled Nd:YAG laser operating at 946-nm

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    We report a new, to the best of our knowledge, record power and efficiency for a 946 nm Nd:YAG laser, producing &gt;110 W (5 TWm −2 sr −1) with a slope efficiency of 80%, with respect to absorbed pump power, and an optical-to-optical efficiency of 74%, with respect to incident power. To achieve this performance, we utilized a closed-cycle acoustic Stirling cryostat to maintain the gain medium temperature at ∼80 K and direct in-band pumping with a volume-Bragg-grating stabilized diode laser bar operating at 868 nm. Daily operation, including cycling of the laser crystal temperature, akin to a comparable water-cooled solid-state laser system, is demonstrated. </p

    Locked rotor and transient tests of a 100 kW HTS machine

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    Locked rotor and “short circuit at the stator terminals” are two standard motor tests that provide operators with useful data about the electro-mechanical performance of rotating machines for installation. A programme of motor tests was performed on a novel machine with an HTS rotor winding and a conventional copper wound stator. The rotor winding was cooled down to 77 K. The differences when driving 0 and 190 A in the stator winding whilst ramping the field current in the locked rotor close to its critical current are discussed by interpreting small changes in the voltages measured at different locations in the winding. The perpendicular field generated by the stator produced the greatest impact on the HTS winding and its starting torque. Finally, a comparison of single-phase short circuits with three-phase short circuits unveiled a doubling in the peak stator current induced and the period for the transient to dissipate, but a moderate reduction in the peak (spiking) current in the HTS winding

    Dataset for: Highly efficient 110-W closed-cycle cryogenically cooled Nd:YAG laser operating at 946-nm

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    This dataset supports the publication: Shayeganrad, G. et al (2020). Highly efficient 110-W closed-cycle cryogenically cooled Nd:YAG laser operating at 946 nm. Optics Letters. doi:10.1364/OL.401011</span

    Temperature and background field dependence of thermal stability in a compact MgB2 solenoid coil

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    A conduction cooled compact react and wind MgB2 solenoid magnet was tested for quench propagation and minimum quench energy MQE in a background field which allows to an extent a decoupling of the peak field in the windings from the conductor field performance. MQE and propagation data was taken in self field at 30, 30.5 and 31.5 K and at fields/temperatures of 1 T/25 K, 3 T/18 K and 5 T/10 K where the power law n-value characteristic was similar at n~30. At all temperatures and at low I/Ic quench propagated first through the insulating layers, in a radial direction, and at high I/Ic within the layer. The MQE values as a function of I/Ic are shown to consistently have non zero values as I? Ic which is characteristic of an analytical quench model that includes the n-value power law dissipation. At 30.5 K a sharp drop in MQE occurs along with the change in propagation direction. The analytical model is then exploited as 1D adiabatic, 3D infinite solenoid, and 3D with heat transfer at the boundary to explore the affect of dimensionality and conduction cooling on the propagation and MQE behavior