Hydraulic characteristics of long nitrogen cooling channels

We have developed two types of long cooling channels to study the hydraulic characteristics of superconducting power cables. At first, we have conducted cooling tests of a 100 m-long duplex-counter-flow channel with liquid nitrogen and observed two kinds of flow instabilities. One is the density wave oscillation and the other is the Ledinegg instability. Secondly we have conducted cooling tests of a 500 m-long channel with three dummy cores simulating superconductors and obtained basic data of initial cooling and temperature distributions along the channel. Oscillation conditions have been checked according to the Ledinegg instability.