Augmentation scheme of 80 K helium test facility to 65 K using sub-cooled liquid nitrogen

The recent trend of High Temperature Superconductor (HTS) developments and HTS based applications has led to the exploration of various method for achieving cryogenic temperature suitable for the HTS applications. Liquid nitrogen (LN2) is a widely accepted choice for HTS applications, however, there is always an urge to reach a temperature lower than 77 K (normal boiling point of LN2) for wider usage of HTS using LN2. In a way forward for creating test facility for HTS and other cryogenic tests, an existing Prototype Cryoline (PTCL) test facility at ITER-India cryogenic laboratory (IICL) has been augmented to deliver 80 K helium for small scale experiments and tests at 80 K. The facility is proposed to be further augmented to achieve 65 K by sub-cooling of LN2 by bath evacuation method. The paper describes the details of the augmentation of the IICL. The LN2 sub-cooling system and its integration to the 80 K helium system have been proposed with supporting process analysis. The equipment sizing of the proposed LN2 sub-cooling system has been inferred based on the process calculations. It is shown that 65 K helium at application end can be achieved with the proposed scheme.