Superconducting Solenoid (7 T) Indirectly Cooled by Cryocoolers for THz Radiation

The results of testing and performance characteristics of an indirectly cryocooled superconducting solenoid to be used at the tehrahertz (THz) spectroscopy experimental station of the free-electron laser at the Institute of Nuclear Physics are presented. The superconducting solenoid with a winding diameter of 102 mm and a length of 0.5 m is designed for a magnetic field of 6.5 T. A warm diameter of 80 mm is available for THz spectroscopy experiments. A superconducting wire Cu/NbTi = 1.4 is used. The design implements passive protection methods due to sectioning and secondary connected circuits in case of a sudden quench. The required field uniformity of 0.5% is ensured by using an iron yoke and additional side windings. The cryogenics of the solenoid is based on two Sumitomo HI cryocoolers. The solenoid and iron yoke are cooled by the second stage of the cryocooler via copper plates. The manufacturing technology of the solenoid is described in detail. The solenoid is tested in a liquid-helium bath and in its own cryostat. Its characteristics meet the requirements of the experimental station. The obtained field of 7.3 T is greater than the designed one due to overcooling up to 3.6 K. The magnetic field is measured both in a bath cryostat and in the designed cryostat; the results corresponded to the design calculations. The solenoid cooling time is 13 days. The quench happened only twice, at 5.6 and 7.3 T.