[en] The thermal behaviour of binary 70 kA HTS current leads has been simulated numerically. The optimum temperature of the helium and the conductor at the cold end of the heat exchanger have been found to depend on the assumed refrigerator efficiency, the engineering critical current density of the AgAu/Bi-2223 tapes at the envisaged temperature at the warm end of the superconductor and the cross-section of the stainless steel support. Reduced engineering critical current densities as well as enlarged stainless steel cross-sections lead to a larger heat load at 4.5 K. As a consequence, the optimum temperature at the warm end of the HTS is shifted in both cases to lower values. When the efficiency of the intermediate temperature cooling cycle providing helium gas of the temperature T_in is enhanced with respect to the efficiency of the 4.5 K cooling cycle the optimum temperature at the warm end of the HTS is shifted to lower values. Considering ideal cooling cycles the optimum intermediate conductor temperature (warm end of HTS, cold end of heat exchanger) is between 75 and 80 K for a stainless steel cross-section of 40 cm² and a total length of 1360 mm (HTS and heat exchanger without connections). The optimum difference of the conductor and the helium temperature at the cold end of the heat exchanger is approximately 20 K. However, even for a conductor temperature of 65 K and a helium inlet temperature of 45 K the required refrigerator input power needed to cool the current lead is only slightly enhanced. In the case of real cooling cycles the optimum intermediate conductor temperature is between 70 and 80 K for a stainless steel cross-section of 40 cm² and a total length of 1360 mm. The . optimum difference of the conductor and helium temperature at the cold end of the heat exchanger is approximately 15 K. The safety requirements in the case of loss of flow favour a design with small values of j_op/j_e, a low temperature and an enhanced stainless steel cross-section at the warm end of the HTS. Reduced operating current densities and a lower warm end temperature provide an enhanced temperature margin. A large stainless steel cross-section increases the heat capacity of the HTS part of the current lead. Both measures would considerably prolong the time available to discharge the toroidal field coils in the case of loss of flow. (author)

[en] The reactive liquid infiltration (RLI) technique, applied to the MgB₂ material, has allowed us to obtain either bulk or wire samples of good transport properties. The evaluation of the voltage-current characteristics, V-Iⁿ, for typical samples, measured by transport at temperatures between 4.2 and 30 K, is presented. The behaviour of the n exponent is discussed in terms of a simple model and the differences between bulk and wire samples are outlined

[en] Superconducting Bi-2212/Ag wires and tapes have been fabricated by the ''powder in tube'' method. Using three-stage annealing, the scatter in j_c data has been reduced to typically 10 % for the wires. Average critical current densities up to 79,000 A/cm² (B = 0) and 28,000 A/cm² (B = 12 T) have been reached at 4.2 K. For textured Bi-2212/Ag tapes j_c values of about 40,000 A/cm² at 4.2 K and B = 12 T have been achieved. X-ray diffraction indicates imperfect grain alignment

[en] Highlights: • Investigation of the cyclic load degradation in the HTS cable prototype is performed. • Results of transverse load fatigue tests on the HTS strands at 77 K are presented. • Design of the new HTS cable prototype for the DEMO CS coils is discussed. - Abstract: Various DC tests performed recently with full-size 60 kA HTS cable prototypes in the EDIPO test facility demonstrated that proposed design of HTS strand at Swiss Plasma Center (SPC) – stack of HTS tapes twisted and soldered between two copper profiles – is applicable for high-current fusion cables, but improvement of the strand mechanical properties against the cyclic loading is still needed. Based on experimentally obtained correlation between the performances of cable prototypes at different operating conditions, further investigation of cyclic transverse load on the strand performance was performed at 77 K. Aiming to obtain a strand design able to withstand a continuous cyclic load operation of some thousand cycles, influence of the strand geometry and tape's manufacturer has been studied. Cyclic load has been applied up to 1000 cycles for straight and bent samples at the load amplitudes up to 4 MPa. Based on the obtained data, next design of HTS cable prototype will be discussed.

[en] In the framework of the conductor optimisation task (CONDOPT) five NbTi subsize cable-in-conduit conductors with parametric variations were fabricated. The DC performance of these conductors tested in the SULTAN test facility [IEEE Trans. Appl. Supercond. 12 (2002) 520] and the strand properties including the voltage-current characteristic, are compared. The results clearly indicate that the current carrying capacity of the conductors is considerably reduced due to the self-field. In conductors with a hindered interstrand current sharing, the critical current has been found to be even below the predicted value at the peak field, suggesting an uneven current distribution among the strands

[en] The effect of transverse compressive stress on the critical current of solder-filled and unfilled Nb₃Sn cables is reported. The conductor used in this study is a Nb₃Sn Rutherford cable manufactured with a bronze-process wire of 0.92 mm diameter. Like epoxy-impregnated cables, solder-filled cables exhibit much less degradation than wire samples when subjected to the same stresses. On the other hand, unfilled specimens are irreversibly damaged at the thin edge when loaded to 160 MPa, and show significantly higher degradation than similar specimens of the solder-filled cable. A finite-element calculation of the stress state inside a particular composite superconductor indicates that more compressive stress is developed in the virgin wire than in a straight wire segment in a real cable environment

[en] The PAC surface investigations are performed by utilizing the radioactive ¹¹¹In probes deposited at the copper crystals surfaces. PAC time spectra are shown for the three main orientations of the copper system Cu(111), Cu(100) and Cu(110). 8 refs., 6 figs., 1 tab. (author)

[en] The current status of surface hyperfine fields measured with NMR, Moessbauer spectroscopy and PAC is reviewed. Emphasis is put on experiments with well-characterized, free surfaces and on results on surface electric field gradients. Applications to detection of probe sites and diffusion phenomena are discussed. (orig.)

[en] The PAC method was applied to study interface compound formation in thin In/Sb film couples. Above annealing temperatures of 220 K, kept for 10 min, the compound InSb is growing out of the interface. The average thickness of InSb increases with the square root of time at the beginning, indicating a diffusion controlled start of interface compound growth. (orig.)

[en] The electric field gradient at ¹¹¹In probe atoms on Cu(100) surfaces was studied. At clean surfaces all probes are exposed to a well-defined surface field gradient. This is used to investigate indium surface diffusion, where the applied PAC method allows to observe diffusion steps on an atomistic scale. The jump rate for indium on Cu(100) was found to be in the order of 10^-3 Hz at 200 K. (orig.)