Study on the Operation Safety of HTS Current Leads in EAST Device

摘要

The experimental advanced superconducting tokamak (EAST) device providing excitation currents to the superconducting magnet system using 13 pairs of high temperature superconducting (HTS) current leads. It is the first fusion experimental device using HTS current leads in the world. However, there are some problems on the HTS current leads during the operation process since 2006. These problems are the key risks to the operation safety of the HTS current leads and EAST tokamak. Some solutions have been putted forward. Supercritical helium (SHe) leakage was found in the HTS current leads in 2011. It led a vacuum degeneration in the cryostat where the HTS current leads were installed. A new connecting structure between the HTS module and low temperature superconducting wires has been used to eliminate the SHe leakage problem. The flow of liquid nitrogen (LN2) cooling loops has been modified to guarantee the existence of LN2 in the cylinders at the middle of the current leads. It can avoid the quench in the HTS current leads due to the loss of coolant. And the measurement sensors have been increased to reliably monitor the temperature in the LN2 tanks to ensure the existence of LN2 in the LN2 cylinder. A water cooling structure has been added in the room temperature terminal of the toroidal field HTS current leads to avoid a temperature fast rise incident on the warm end of the resistive heat exchanger and the returning nitrogen gas under large transmission current. The operation safety of the HTS current leads in EAST device has been improved after the upgrade.