Solid cryogen: a cooling system for future MgB2 MRI magnet

An efficient cooling system and the superconducting magnet are essential components of magnetic resonance imaging (MRI) technology. Herein, we report a solid nitrogen (SN2) cooling system as a valuable cryogenic feature, which is targeted for easy usability and stable operation under unreliable power source conditions, in conjunction with a magnesium diboride (MgB2) superconducting magnet. The rationally designed MgB2/SN2 cooling system was first considered by conducting a finite element analysis simulation, and then a demonstrator coil was empirically tested under the same conditions. In the SN2 cooling system design, a wide temperature distribution on the SN2 chamber was observed due to the low thermal conductivity of the stainless steel components. To overcome this temperature distribution, a copper flange was introduced to enhance the temperature uniformity of the SN2 chamber. In the coil testing, an operating current as high as 200 A was applied at 28 K (below the critical current) without any operating or thermal issues. This work was performed to further the development of SN2 cooled MgB2 superconducting coils for MRI applications.