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The authors regret a mistake in simulations of the excitation coils. As a result, the used field strengths are much smaller than mentioned in the paper. In the paper we described that the AC field is 0.5 mT and the DC field is 50 mT at the location of the sample. However, this should be 0.2 mT AC and 3.3 mT DC. This won’t affect any of the results or conclusions described in the paper. We think it is even more promising that the method works this well at these low field strengths. The authors would like to apologise for any inconvenience caused.

In the last decades, various methods have been used to characterize superconducting behavior versus axial strain. In cooperation with the University of Twente (UT), the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) built a facility practically similar to the so-called “Pacman” spring device. The facility allows critical current measurements of an Nb3Sn strand at different temperature, magnetic field and applied axial strain. In the process of validating the new setup, an ITER Internal-Tin (IT) strand, which has also been measured at the UT, is tested with the ASIPP Pacman. The ITER IT wire has an irreversible strain limit around +0.3%. At ASIPP, the strand was characterized in a magnetic field from 10 to 13 T and applied axial strain from -0.7% to +0.5%. Similarities of the data obtained (IC(ε), IC(B) and irreversible strain limit) from the two institutes were remarkable.

For the ITER Central Solenoid (CS), with Nb 3 Sn CICCs that operate under fast ramping conditions, the selection of the twist pitch lengths can have a significant impact on the performance. The critical current and temperature margin are influenced by the thermal contraction of the composite materials, the transverse electromagnetic forces, and coupling currents. The numerical cable model JackPot-ACDC is developed to calculate the interstrand coupling loss for any time-dependent current and magnet field for all strand trajectories in a CICC. It was a priori predicted that the amount of coupling loss and critical current degradation is subject to interference due to different subcable twist pitches. Here test results are discussed of the ITER CS conductor sample, manufactured according to the proposed design, optimizing the transverse load degradation, the temperature margin, and the coupling loss.

The intrawire resistance and alternating current (AC) loss of two MgB2 wires with filaments surrounded by Nb barriers have been measured and analyzed. Relatively high values of filament to matrix contact resistivity are found in the MgB2 wires; the values are two or three orders higher than those commonly found in NbTi or Nb3Sn wires. Considering the high porosity of the MgB2 filaments cold high pressure densification has been applied on the two MgB2 wires to investigate its impact on intrawire resistance and AC loss. The intrawire resistance is measured with a direct four probe voltage current method at various temperatures. The AC loss is measured by vibrating sample magnetometer measurements at 4.2 K. In addition to the intrawire resistance measurements the critical current of MgB2 wires before and after densification is measured with a U shaped bending spring at 4.2 K as function of axial strain. The critical current in densified MgB2 wires is found to be higher than that in the same wire without densification; it is also less sensitive to the applied axial strain.

A magnetic Pulse Test Facility (PTF), in which samples of CICC electrical joints from each ITER home team will be tested, has been fabricated at the MIT Plasma Fusion Center under an ITER task agreement. Construction of this facility has recently been completed, and an initial test phase on the first CICC joint sample has begun. PTF includes capabilities for sample currents up to 50 kA from a superconducting transformer developed by the University of Twente, magnetic fields up to 6.6 T with ramp rates to +1.5 T/s and -20 T/s, and a cryogenic interface, supplying supercritical helium with flow rates to 20 g/s through each CICC leg at controlled temperatures to 10 K and pressures to 10 atmospheres. A sophisticated, multiple-channel data acquisition system is provided to processed, digitally recorded sensor signals from both the sample and the facility. The facility is totally remote-controlled from a control room through a fiber optic link, and qualified users worldwide are afforded secured access to test data on a 24-hour basis via the Internet. The facility has successfully exercised the first joint sample over the ITER test spectrum with positive results

A method to increase the efficiency of a power system for a superconducting (SC) magnet is presented. The system links a magnet and the mains (which serves as a power source and/or a load). It contains both room and low temperature electrical components. In order to reduce heat leaks, it is proposed to use a semiconducting converter unit located in the same cryostat and which is connected via high current leads to a magnet and via low current leads to the mains. In the standby mode the temperature of the unit is close to that of a magnet. While operating, the temperature of the unit will rise up to a level normally allowed for such components (~400 K for the switches). The efficiency of the proposed scheme is close to the conventional one which is based on a semiconducting power supply placed at room temperature in combination with retractable current leads. To demonstrate the approach, we developed such a converter. The performance of the converter unit is demonstrated while ramping a current of a small SC magnet operating at 4 K. Characteristic in- and output currents are 2 A and 300 A respectively. The unit standby temperature is measured to be ~40 K, while the operating temperature is about 300 K. Reasonable energy efficiency is demonstrated even at a low powering voltage.

In order to test superconducting cables at high currents it is convenient to generate the required transport current inductively, i.e. by means of a superconducting transformer. The paper gives a survey of the devices in different laboratories that apply this technique to test cables above 20 kA. An existing test facility at the University of Twente, suitable for 50 to 200 kA, is treated in more detail. Specific aspects of such a facility are discussed, for example the design of the transformer, the methods to measure the current in the superconducting secondary circuit and the fabrication of joints with a sufficiently low electrical resistance.