Analysis of the electrodynamics of subcable current distribution in the superconducting POLO coil cable

Unexpected ramp rate limitations (RRL) found in superconducting magnets during the development of magnet systems can be attributed to a current imbalance amongst the cabled strands which leads to a lower than expected quench current. In superconducting magnets the current distribution in the cable during ramping depends mainly on the electromagnetic properties of the system. A detailed analysis of principle causes for RRL phenomena was performed with a model for one half of the POLO coil considering the complete inductance matrix of the cable and the fact that all turns are mutually coupled. The main results of these calculations are that unequal contact resistances can not be responsible for RRL phenomena in coils with parameters comparable to those of the POLO coil and that already minor geometrical disturbances in the cable structure can lead to major and lasting imbalances in the current distribution of cables with insulated and non-insulated strands. During the POLO experiment the half-coil model was employed to get a better understanding of the measured compensated subcable voltages during quench. The good agreement of the calculated and measured results demonstrates the validity of the model for RRL analyses. (orig.)27 refs.Available from TIB Hannover: ZA 5141(5653) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Test program preparations of the ITER toroidal field model coil (TFMC)

The preparative experimental and analysis work as well as the code development for testing the ITER (International Thermonuclear Experimental Reactor) TFMC, one of the large projects of the ITER research and development programme, is described. The expected critical currents of the Nb3Sn superconducting cable are derived from the numerous short sample strand and subcable measurements. A data set of the thermo-hydraulic properties of the bundle conductor with a central channel was elaborated in experiments as an input for the thermo-hydraulic calculation codes GANDALF and MITHRANDIR combined with the hydraulic network code FLOWER. On this basis, the quench behaviour and the injection of gaseous heated helium slugs for determining the operation limits are treated. The mechanical behaviour of the test configuration was investigated by a finite element calculation. The winding type in which the conductor is embedded in radial plates has to be considered for transient voltage peaks as an electrical network. Arising over-voltages by resonance frequencies in the winding pack have to be considered for the integration of the electrical insulation system of the TFMC. Numerous sensors are installed to compare the predicted values and behaviour with the measurements. (C) 2001 Elsevier Science B.V. All rights reserved