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Two constraints on semi-continuous magnet coils are the strength of the winding material, and the maximum power which the rectifier must deliver for a short time. Here we assume that for a 60-T coil wire of sufficient strength (about 100 kg/mm2 is available. It was shown earlier that a single, homogeneous coil needs a power of nearly 150 MW, which calls for huge capital investments in power lines, transformers, switches and rectifiers. By using two nested coils, wound from wires with different strengths and current densities, and energized successively by the same rectifier, we can reduce the power to less than 50 MW.

A sample of YBa 2 Cu 3 O 7 was constructed by stacking a number of small single crystals. Magnetization measurements were made in magnetic fields up to 38 T, both parallel to the c -axis and to the basal plane. At 1.4, 4.2 and 20.4 K, a large irreversible magnetization was observed. The significance of these results for the superconducting properties is discussed.

An overview is given of the high-field installation of the University if Amsterdam now in operation; this installation can generate fields up to 40 T, constant within 8 mT for about 80 ms. Recent improvements of the regulation of the field are discussed, as well as some examples of recent measurements.