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Cryocoolers are increasingly favored over bath or forced-flow cooling systems for providing heat removal and thermal stability in High Temperature Superconducting (HTS) magnets. Efficient heat transfer between coil and cryocooler is crucial to the operation of such a system. Compared to conventional thermal buses, which are typically made of solid materials such as high-purity copper braids, the Pulsating Heat Pipe (PHP) -a passive device that operates through thermally induced two-phase flow- offers superior heat transfer performance at a reduced mass. PHPs are commonly constructed from a capillary sized tube bent in serpentine between an evaporator (in contact with the coil) and a condenser (in contact with the cryocooler). This configuration minimizes the bulk while allowing large areas of the magnet to be cooled. The tube is filled with a cryogenic fluid at saturation conditions. Heat is efficiently transferred by a combination of latent and sensible heat transfer mechanisms. In addition to being efficient, lightweight, and passive, it functions as an autonomous thermal bus and switch, capable of operating in zero-gravity, high-magnetic-field and high-radiation environments. For these reasons, the Paul Scherrer Institute (PSI), in collaboration with the VDL Enabling Technologies Group (VDL ETG), has launched a project to design, manufacture, characterize, and apply cryogenic PHPs for enhancing the cooling efficiency and reliability of cryocooler-based HTS magnets. This project belongs to PSI’s SMILE (Superconducting Magnets to Improve the Efficiency of Large Research Facilities) program that seeks to develop efficient energy superconducting magnet technology that will increasingly replace resistive magnets currently in use in large research facilities of the Paul Scherrer Institute.
This work presents an experimental comparison between conventional copper braids and neon-filled PHPs used as thermal links between a cryocooler and an HTS coil. The objective is to compare magnet coil temperatures obtained with neon PHPs and copper braids having the same cross-section and adiabatic length, for transferring heat generated by AC losses in an insulated HTS coil. The coil was tested with currents varying from 0 to 500 A, using ramps of 500 A/s and a 0.1 s plateau. The dedicated test bench developed at PSI is first described, followed by the HTS coil, the PHPs, and the copper braids used in the experiments. Finally, the experimental results obtained with neon PHPs and copper braids are analyzed and compared, demonstrating proof of concept and quantifying the heat transfer improvement achieved with neon PHPs.
| Submitters Country | Switzerland |
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| Are you a student? | No |
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