Speaker
Description
SST-1 is a medium size superconducting (SC) tokomak operational at IPR in India. TF and PF sc coils are used to produce high magnetic field strength. Presently, 10 kA rated Vapour cooled current leads (VCCLs) for TF system is made of NbTi superconductor and copper heat exchanger. Similarly, 9 PF coils will be energised by individual power supplies requiring total 18 VCCLs under pulse operations up to 9 kA. VCCLs utilize 55% of total cryogenic plant capacity (1.3 kW at 4.5 K). Consequently, it has been envisaged to minimize the liquid helium consumption by an innovative solution to save cryogenic power with alteration of materials in the current lead specific to pulse operation. This approach adopts two folds savings, i.e. introducing MgB2 sc in lieu of NbTi and the heat exchanger material as brass instead of copper, which has more specific heat, lower thermal conductivity and higher melting temperature compared to copper. Moreover, brass can also be overloaded. MgB2 provides better temperature margin as compared to NbTi. In temperature range of 20 K – 40 K, cryo plant offers the best exergy efficiency. It has been established that the combination of MgB2 and brass based current leads have several advantages over the existing VCCLs. To support this statement, a prototype experiment was conducted using a dedicated test cryostat in which both types of current leads were installed and tested up to 1.5 kA. This test involves cryostat, current leads, feeder link, hydraulic network, 12 kA/16 V switch mode power supply, sensors and data acquisition system. This paper highlights the test set-up details and experimental results along with comparison of liquid helium consumption between NbTi/Cu and MgB2/brass current leads to assess the operational cost. It also discusses the cryo benefits of MgB2 based brass current leads.
