Status of HTS current leads for WENDELSTEIN 7-X and JT-60SA

Abstract

The stellarator WENDELSTEIN 7-X (W7-X) and the satellite tokamak JT-60SA will use High Temperature Superconductor (HTS) current leads to reduce cryogenic load and operational cost. Forschungszentrum Karlsruhe is in charge of design, construction and test of these HTS current leads. For W7-X fourteen current leads with a nominal current of 14 kA and a maximum current of 18.2 kA are required that are oriented upside down with the room temperature end at the bottom. JT-60SA is constructed in the frame of the Broader Approach Agreement and will use 26 current leads mounted in vertical, normal position with room temperature end at the top. All current leads will consist of an HTS part using Bi-2223 conductor and a classical Cu heat exchanger. The Cu heat exchanger covers the range between 60 K and room temperature and will be cooled with 50 K He while the HTS part is conduction cooled, only. For simplicity a common basic design of the current leads for W7-X and JT-60SA is planned which requests that the current leads work independently of the orientation, and from the experimental boundaries given by W7-X and JT-60SA the current leads have to withstand a loss of He coolant for more than 10 min and allow a discharge of the magnet system although a quench of the HTS part has happened. JT-60SA gives the more critical HV requirement with a Paschen tight insulation of 21 kV. All current leads shall be designed for low thermal loads, under full current and in standby mode. The paper will give details of the actual design status of these current lead developments for W7-X and JT-60SA based on a common basic design.