Design of current leads for Beijing electron and positron collider upgrade

For Beijing Electron-Positron Collider Upgrade (BEPC II), six pairs of current leads with four different currents were used for superconducting quadruple magnets (SCQ) and a pair of 4000 A current leads were used for the superconducting solenoid magnet (SSM). Multi-tube current leads for SCQ and SSM magnets were designed. The special feature of the leads is that a copper block is added to the cold end of the leads to delay the time for runaway in case of the cooling helium being interrupted. The numerical simulation results on steady and unsteady thermal processes by CFD software package Fluent6.0 are also presented. (authors)