TIEMF in unirradiated Cu cored MI cables: Microstructure

Radiation and temperature induced currents and voltages in MI cables (generally termed RIEMF and TIEMF, respectively) have been the object of discussion and study. The problem is due to the observed generation of a voltage along the centre conductor of MI cables due to temperature gradients, particularly large for Cu cored cables. It has been confirmed that these voltages are generated in well localized regions of the cable, suggesting that some inhomogeneity is present, however no geometric variations have been observed by X-ray imaging of the cable core and sheath. Furthermore, no annealing or modification of the sensitive regions has been observed for heating up to 550 °C, indicating that the problem was not related to work hardening effects in the copper. Work has now been started to examine in detail the sensitive regions of the Cu cored MI cables. Sections of the Cu core extracted from the MI cable have been examined by optical and scanning electron microscopy. An important result is the observation of severe surface damage for the Cu wire extracted from the MI cable, compared with the highly polished surface of bare Cu wire. These observations, together with the impurity analysis, are presented.