J. Yamamoto

K. Ishibashi

K. Maehata

M. Mizokani

M. Takeo

T. Mito

National Institute for Fusion Science (NIFS-Repository)

§26. Stability of High-Temperature Super-conducting Current Leads Ishibashi, K., Maehata, K., Mizokani, M., and Takeo, M (Kyushu Univ. Eng.) Mito, T., and Yamamoto, J. For examination of the stability of high temperature superconducting (IITS) leads, the temperature perturbation is applied to the steady-state temperature profile. In this work, to simplify the transient analysis of the fiTS leads, the conductor is assumed to be cooled by ideal heat-exchange with cooling gas. For the ideal gas cooling, the heat conduction equation of the conductor of IITS leads is generalized as, _aj A. aT)+ F(T',.,.D2 _ MC naT =caT ali\ au JP g""' au a-r: . ( 1) The critical current of the IITS conductor can be approximated to decrease linearly with increasing T. If I is equal to the critical current of fiTS conductor at Tsh• the current sharing factor in eq. ( 1) is given by (2) Equation (1) is solved for given D = Ills with the boundary conditions of T = 4.2 and 77K at u = 0.0 and 1.0, respectively. The cooling gas is assumed to be supplied by the evaporation induced by the heat leak from the leads supplies, i.e. M = Qc llh. In the case of aT I irt = 0, solutions of eq. (1) give the equilibrium temperature profiles along the conductor of gas-cooled HTS leads. We found the intermediate solution between the well-known upper- and lower-solutions. The domain of the normal conducting state exists in the conductor of the intermediate solution similar to that of the upper sol uti on. The stability of the fiTS leads is examined by the transient behavior of the temperature profile of the conductor by applying a temperature perturbation of ±sin(nu) to the equilibrium solutions. Transient behavior of perturbed temperature profile is numerically analyzed by solving eq. ( 1 ). Since each perturbed temperature profile recovers to the upper- and lower-solutions, respectively, the upper- and lower-solutions are 32 confirmed be stable against the perturbation. By applying the temperature perturbation sin(nu), the temperature profile of the intermediate solution grows to those of the upper solution. In contrast, the perturbed temperature profile of the intermediate solution by -sin(nu) falls to the lower solution. If an accidental thermal disturbance raises the temperature profile of the conductor below that of the intermediate solution, the lead recovers to the state of the lower solution. Therefore, the unstable intermediate sol uti on is regarded as a measure of the recovery criterion for the thermal disturbance. The stability of the conductor is explained by the integral S h of the specific heat along the conductor between the intermediate- and the lower-solutions. The stability parameter S h obtained for the ideal gas-and the conduction-cooled leads is calculated for various values of D and shown in Fig. 1 with the heat leak Qc of the lower- and intermediate-solutions. The rise time of the peak temperature of the conductor is the important quantity as a reliability index against accidental thermal disturbance. In this work, a tolerable peak temperature is taken to be 300 K. The rise time 'tu in the case of thermal disturbance above the recovery criterion is estimated from the transient analysis of the temperature profile obtained by applying the perturbation of sin(nu) to the intermediate solution of the gas- and conduction-cooled leads. The evaluated values of 'tu are plotted in Fig. 1. Fig. 1 D [A/m] Stability parameter S h• heat leak (2c and rise time 'tu as a function of the geometrical parameter D. _g and _c represent the ideal gas- and conduction-cooling, respectively. 

Stability of High-Temperature Superconducting Current Leads

Abstract

Similar works

Full text

Available Versions

National Institute for Fusion Science (NIFS-Repository)