Operation Modes of a 50-60 Hz Superconducting Converter

The operation at mains frequency of 50–60 Hz allows for a simplification of the superconducting converter construction at a reasonable efficiency of 96–98 % (while pumping up and down a superconducting magnet). Besides, new possibilities appear in the interaction between the mains and the magnet via the converter. The operation modes of a new superconducting converter connected to the mains and to the superconducting magnet are considered in the paper. The converter ‘cold’ part consists of the fast response thermally controlled switches, a non saturated iron core superconducting transformer and the current sensors in the branches. The PC-based control unit includes “direct” and “shunting” switches and allows to realise various algorithms of the converter control. It is shown that both AC to DC, and DC to AC conversion with the magnet-mains energy exchange in both directions via the converter can be realised. In the paper such an operation is described theoretically and verified by the physical and numerical experiments

Electrical Resistance of Superconducting Cable Splices

The electrical resistance of superconducting cable splices is known to be in the 10{sup -9} {Omega} range which to be measured conventionally would require the use of a micro voltmeter with a power supply capable of generating kilo Amperes plus a liquid helium cryostat with large power leads. Here we present a system for carrying on such measurements that requires besides the microvoltmeter a power supply capable of generating only up to 35 {Alpha} and a 152 mm diameter neck helium dewar using less than 25 liters per day after initial cool down. In this paper we describe the apparatus and present the data taken with it in its first use which for data acquisition used just a chart recorder. The method is based in making the splice in a loop of cable, inducing a current in it and measuring its decay time constant. Generating high currents in superconductors by induction is not a new technique but the use of the decay constant of currents generated this way for the determination of minute electrical resistance seems novel to the author. Unexpected details in the results will be discussed

Bottom-current and wind-pattern changes as indicated by Late Glacial and Holocene sediments from western Lake Geneva (Switzerland)

The Late-Glacial and Holocene sedimentary history of the Hauts-Monts area(western Lake Geneva, Switzerland) is reconstructed combining high resolution seismic stratigraphy and well-dated sedimentary cores. Six reflections and seismic units are defined and represented by individual isopach maps, which are further combined to obtain a three-dimensional age-depth model. Slumps, blank areas and various geometries are identified using these seismic data. The sediment depositional areas have substantially changed throughout the lake during the end of the Late-Glacial and the Holocene. These changes are interpreted as the result of variations in the intensity of deep lake currents and the frequency of strong winds determining the distribution of sediment input from the Versoix River and from reworking of previously deposited sediments within the lacustrine basin. The identified changes in sediment distribution allowed us to reconstruct the lake's deep-current history and the evolution of dominant strong wind regimes from the Preboreal to present times