1.5 T Cryogen Free Superconducting Magnet for Dedicated MRI

A 1.5-T cryogen-free superconducting magnet for a dedicated orthopedic magnetic resonance imaging was developed. The magnet is designed for imaging of human extremities, such as knee, foot, ankle, wrist, and elbow. The magnet has a compact cryostat cooled with a pulse tube coldhead. The first stage of a coldhead is used to cool the radiation screen. The second stage of a coldhead with the cooling power of 1 W at 4.2 K is connected by copper bars to mandrels of superconducting coils. The coldhead is mounted in a special vacuum chamber separated from the magnet vacuum vessel to facilitate the coldhead replacement. The warm bore of a cryostat is 325 mm in diameter and 600 mm in length. Superconducting coils are wound with niobium-titanium wire on the mandrels made of aluminum alloy. The windings are optimized for high homogeneity of a magnetic field in a DSV of 160 mm. The magnet is actively shielded. The 0.5 mT fringe field is located at 1.7/2.5 m from the magnet center in radial/axial directions correspondingly. The magnet is equipped with HTS current leads. The magnet design is presented.