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The main coils of the new European DIPOle (EDIPO) test facility, which is able to provide a background magnetic field up to 12.35 T, were commissioned at the Center for Research in Plasma Physics in July 2013. A field homogeneity of +/-1% was achieved over a 900-mm length, as compared to SULTAN's 10.9 T over 425 mm. To complete the commissioning of the test facility, the new superconducting transformer has been operated in 2015, and a high-current NbTi sample, which was earlier tested in the SULTAN test facility, has been tested in EDIPO under the same conditions as in SULTAN to benchmark the results. During the initial commissioning of the 100-kA transformer in 2013, the primary coil was found to be insufficiently cooled due to the debonding of the primary winding from its former that also served as the liquid helium cryostat. The NbTi primary coil was therefore modified to be in direct contact with liquid helium. At the next attempt of commissioning, in March 2014, a mechanical failure due to the imperfect alignment of the primary and secondary windings caused major damage. A replacement primary coil, which was wound in Summer 2014, was used in the third commissioning campaign in November 2014, but it failed due to the poor impregnation of the NbTi winding. Eventually, the original primary winding was repaired and commissioned in April 2015. The commissioning included a calibration of the current meter for the secondary winding and the high-current test, i.e., up to 95 kA at various background fields, of the “Trasek” conductor sample, which is a rectangular cable-in-conduit conductor made of 324 SnAg-coated NbTi strands. An excellent agreement was found between the results obtained from the two facilities. The sample holder unit is also equipped with a high-temperature superconducting (HTS) adapter and a counterflow heat exchanger to allow testing in EDIPO of HTS high-current samples over a broad range of operating temperatures, from 4.5 up to 50 K.

The performance of two mass-produced Nb3Sn conductors for the ITER central solenoids was tested for the first timmass-produced Nb3Sn conductorse. One was cut from the forward end of an 80-m-long conductor, and the other was cut from the forward end of a 918-m-long conductor. The fifth-stage twist pitches of these conductors were lengthened by approximately 16% during cable insertion and compaction with conduit. The current sharing temperatures Tcs were measured over 20 000 electromagnetic cycles, including four thermal cycles between 4.2 K and room temperature. The Tcs of the former conductor increased and became almost constant through the cycling. In contrast, Tcs of the latter conductor not only increased but also decreased slightly against cycling. The Tcs decline rate after 10002 cycles was -4.50 × 10-6 K/cycle. If this rate is assumed to continue after 20000 cycles, Tcs would decrease by -0.27 K over 60000 cycles. Even so, Tcs is higher than an acceptance criterion of 6.5 K at 60 000 cycles. The ac losses Q of both conductors at a current of 0 kA were almost the same as or slightly lower than Q of a short sample conductor whose fifth-stage twist pitch was not lengthen. On each conductor, Q at 40 kA was approximately 10% higher than that at 0 kA; thus, the effect of the transport current on Q was not large.

The correction busbar (CB) conductors for the ITER project are being produced in China. The second China CB conductor sample (CBCN2, Phase II of conductor testing) and the third CB conductor sample (CBCN3, Phase III testing) were made of the WST NbTi strands, cabled by Changtong, jacketed at ASIPP, and tested in the SULTAN facility. The current sharing $(T_\mathrm{cs})$ test results show that the conductor sections of CBCN2 and CBCN3 have high $T_\mathrm{cs}$ performance. Using the electrical method, the $T_\mathrm{cs}$ of both CBCN2 and CBCN3 samples was 7.50 K at 10 kA/2.9 T (maximum operating field) before and after electromagnetic loading. AC loss measurement was performed before any electromagnetic loading of the sample, and the measurements were repeated after 1000 or 2000 cyclic loads. The AC loss measurements were performed at 2-T background field, without transport current. The ac loss of the CBCN2 and CBCN3 conductors slightly differs at ±0.2T ac field and various frequencies. According to the SULTAN test result, $T_\mathrm{cs}$ of CBCN2 and CBCN3 conductor samples meet the ITER acceptance criteria of 7.0 K at Bpeak field is 2.9 T and 10 kA.

In the last few years, the critical temperature (T c) of several ITER cable-in-conduit conductors (CICC) was determined by magnetization measurements at zero current. The distribution of the critical temperatures (T c), caused by variation of strain in the Nb3Sn strands, was found to vary with the number of load cycles. A comparison with mechanical modelling requires the strain distribution, while the T c distribution is sufficient to determine the CICC performance. The current sharing temperature (T cs) is calculated supposing that the measured distribution of T c is representative of its variation along a single strand and that the current is uniformly distributed among the strands. The T cs values, found for background and peak magnetic field, are compared with the results of the DC test in the SULTAN facility. The presented estimation techniques lead to an overestimation of T cs. The differences of the estimated and measured T cs values are discussed including the effect of different current-voltage characteristics of single strands and CIC conductors.

The tilted head race track coils of the EDIPO test facility are wound with cable-in-conduit conductors made by high current density Nb3Sn strands, Jc = 2400 A/mm2 at 12 T – 4.2 K. Since the commissioning of the coils, frequent voltage spikes were observed at the quench detection taps during the low current range of operation, completely disappearing above 2 T. The large amplitude of some spikes triggered the quench detection system: the parameters for protection (voltage thresholds and validation time) had to be modified for the voltage pairs monitoring the windings. The occurrence of partial flux jumps in the high current density strands is known from former characterization. The fast data acquisition of the quench detection system, with 800 Hz sampling frequency, allows investigation of the dynamics and propagation of the voltage spikes in the various layers of the winding. From the collected data of several runs of operation, statistics of amplitude, initial location, propagation and reproducibility were drawn, looking also for correlation with the operation history, e.g. first cooldown, ramp up vs. ramp down, ramp rate, etc. The energy released by the flux jumps is conservatively estimated by the time integration of the voltage spikes and discussed in terms of energy margin and heat removal rate in the layers. In conclusion, the limitation of the use of high current density Nb3Sn strands in high current conductors is discussed.

The tests of the ITER Toroidal Field (TF) full length conductors (hundreds of meters, production phase IV) were started at the end of year 2012 and were performed accordingly to the firmly specified test program. The TF conductors produced by the ITER domestic agencies (European Union, Japan, Korea, and Russian Federation) passed the qualification tests to be used for the TF coil winding. The four ITER Central Solenoid (CS) conductors produced in Japan were tested in frame of supplier qualification tests in order to verify the improved design of the CS conductor operating in cyclic mode and, thus, to solve the issue of drastic performance degradation with electromagnetic cyclic loading observed earlier. The test results of the recently tested ITER conductors are summarized in this paper, and the specific features of the voltage-temperature (VT) evolution in Nb3Sn conductors during the qualification test campaigns are highlighted and compared with earlier tested conductors.

The performance of two conductors for the ITER central solenoids was tested. The current sharing temperatures were measured over 17 050 electromagnetic cycles, including four thermal cycles between 4.2 K and room temperature. declined almost linearly over the 10 000 rated electromagnetic cycles. was nearly constant for 70% of the rated electromagnetic cycles, which implies the existence of a fatigue limit in the conductors. For 85% of the rated cycles, a very sharp degradation of approximately 0.2 K occurred. Some type of large deformation of strands, such as buckling, may have caused this sharp degradation. The effective strain degraded linearly with the electromagnetic force on the cable. The gradient after 10 000 cycles was 1.5 times greater than that before cycling. After 10 000 cycles, the ac losses of both conductors considerably decreased to less than half of those before cycling. These ac losses before cycling were less than a fourth of those of toroidal field conductors. After the test campaign, destructive inspection of the conductor clarified that on average, the distribution of residual strain along the cable was almost uniform at 32 ppm. It was also clarified that some strands were visibly deformed under a high magnetic field, whereas strands under a low magnetic field did not appear to be deformed. The deformations of the central solenoid cable were larger and wavier in subcables than those observed in the toroidal field cable. This plastic deformation of the strands could be one of the major reasons for the degradation during cyclic operation.

The commissioning of the European DIPOle (EDIPO) test facility at the Center for Research in Plasma Physics in Villigen was completed in Spring 2015, and the first test of a 60-kA/12-T high-temperature superconductor (HTS) was carried out in June 2015. User specifications are issued to allow external users to prepare their own sample matching the interface of the test facility. EDIPO offers a background magnetic field up to 12.35 T in a rectangular test well with a cross section of 89 mm $\times$ 138 mm (sample dimension). The homogeneous high field length is 910 mm (±1%) or 680 mm (±0.5%) at full current. A set of small copper coils provides a superimposed ac field with amplitude up to ±0.3 T and frequency up to 1 Hz. A superconducting transformer provides steady-state operating current for the sample up to 100 kA. The cooling circuit of the sample supplies supercritical helium at 10-bar inlet pressure. The mass flow rate, which is adjustable by cryogenic valves, is up to 8 g/s in each branch of the sample at 4.5 K. The operating temperature ranges from 4.5 to 60 K (at high temperature, the range of mass flow rate is reduced). To test samples at temperature higher than 10 K, an HTS “adapter” connects the sample to the NbTi transformer plates, which must remain cold. In such case, the length of the sample is reduced from 3600 mm (typical low-temperature superconductor sample) to 2900 mm (HTS sample with adapter).

We have studied low-temperature magnetic properties as well as high-temperature lithium ion diffusion in the battery cathode materials LixNi1/3Co1/3Mn1/3O2 by the use of muon spin rotation/relaxation. Our data reveal that the samples enter into a 2D spin-glass state below TSG=12 K. We further show that lithium diffusion channels become active for T>Tdiff=125 K where the Li-ion hopping-rate [nu(T)] starts to increase exponentially. Further, nu(T) is found to fit very well to an Arrhenius type equation and the activation energy for the diffusion process is extracted as Ea=100 meV., Submitted to Journal of Physics: Conference Series (2014)