Thermal stability of superconducting magnet system in a tokamak Dr hab. inż. Leszek Malinowski, prof. PS Dr inż. Monika Lewandowska Elevation of the ITER magnet system TF coil conductor design PF coil conductor design CS coil conductor Conductor quantities for ITER magnets Heat loads Thermal stability • Conductors made of pure superconducting material are thermally unstable • Cables constituted of the superconducting material embeded in the normal metal can operate stable. Full stabilization q>Q 2 I I max c R where 1 hPTc To Ic Imax - maximum stable operating current, R - normal state resistance, h - heat transfer coefficient, P - cooled perimeter, Tc - critical temperature, To - coolant temperature. Main disadvantage of fully stable wires is large amount of stabilizer. This implies: • low overall current density of the conductor • large size and big cost of a superconducting device Modern superconducting wires are partly stable. It implies limited amount of energy which can be dissipated in a cable without disturbing its safe operation. Critical energy E Ecr E - energy of dissipation Ecr - critical energy of the conductor. Critical energy - the minimum energy of the thermal disturbance destroying the superconductivity Mathematical model of normal zone m u u u a g su q t x x x Tn V h u ph T h I e Tn - temperature of the n thermal component Vh - volumetric flow in the h cooling channel ph - pressure in the h cooling channel Th - temperature in the h cooling channel Ie - current in the e conducting component Main goals of studies and anticipated results • Identification and quantification of energy disturbances and heat sources in superconducting magnet system in a fusion reactor. • Analysis and modelling of heat transfer phenomena in cable-in-conduit-conductors (CICC) used in fusion reactor magnets. • Development of an analytical model of a normal zone in CICC. • Formulation of stability criteria for CICC. • Performance of sample calculations and validation of the results by comparison with experimental results.