Development of a Compact Measurement System of Transport Characteristics in HTS Conductors by Using an HTS Current
In order to realize HTS power machines and devices with high performance, it is important to evaluate the characteristics of HTS conductors quantitatively. We developed a compact system to measure the transport characteristics of HTS conductors under various experimental conditions. This system enables us to measure the transport characteristics of straight HTS conductors up to a current capacity of 1 kA class at 77 K, 66 K, and 4.2 K. The measurement of transport current losses is done by the Poynting vector method. The distribution of Poynting vectors around the sample conductor can be obtained by using many sets of both potential leads and pickup coils. An HTS current transformer (HTS-CT) is used to feed current to the sample conductor for the measurement. A secondary current of about 1 kA at 77 K can be induced when the primary current is 40 A. The sample conductor is connected to the secondary coil of this transformer. As a sample conductor, we used a conductor consisting of 16 parallel Ag-sheathed Bi-2223 multifilamentary tapes. The joint method between the HTS-CT and sample conductors is also examined. Based on these results, the usefulness of this measurement system is discussed.
Inter-Strand Coupling Losses in Bi-2212 Rutherford Cables
Inter-strand coupling loss measurements were carried out in liquid helium for Bi-2212 Rutherford cables composed of 30 non-twisted strands. Short, straight samples composed of three stuck cables were set in a uniform field space inside the NbTi magnet of race-track and split type. Frequency characteristics of coupling losses were observed for transverse ac magnetic field, both perpendicular and parallel to the flat face of cables. An additional measurement of ac losses was carried out in order to clarify properties of hysteresis losses and intra-strand coupling losses. The obtained effective filament diameter describing the hysteresis loss property indicated that almost all filaments in strands were strongly connected to each other. From both this result and the frequency characteristics of coupling losses for the perpendicular field case, the inter-strand coupling time-constant was given in the order of 10 m. Moreover, the effective contact resistance between crossover strands in the cable was also given in the order of 10-10 Omegam2, which was the same order as that for the NbTi Rutherford cable composed of Cu matrix strands
Thermally Induced Dynamics of Satellite Solar Panels
Thermally induced structural motions are known to affect the attitude dynamics of low Earth orbiting satellites during eclipse transitions. Motions of e exible appendages such as solar panels lead to rigid body rotations of the entire satellite because the total angular momentum of the system is conserved. These potentially large attitude disturbances may violate pointing accuracy and jitter requirements. One type of thermally induced dynamics exhibited by solar panels is thermal snap. The Upper Atmosphere Research Satellite is a prominent example of a satellite that experiences thermal snap disturbances during eclipse transitions. This paper describes recent studies of thermally induced dynamicsof solarpanels, including an analysisofsatelliteattitudedynamics resulting from thermally induced structural motions and a laboratory investigation of the thermal-structural performance of a satellite solar panel. Analytical and experimental results demonstrate thermal bending deformations with acceleration transients that have characteristic thermal snap disturbance histories in response to rapid changes in heating. The studies show that solar panel thermal snap disturbances are caused by through-the-thickness temperature differences that vary at a nonconstant rate. Finite element analysis correctly predicts the thermal snap phenomenon observed in the solar panel experiments.