Design and test results of a BSCCO-2223 magnet for gyrotron application

A program is currently under way to develop a compact, power-efficient, robust gyrotron. Gyrotrons require a very precise magnetic field, typically generated by a NbTi superconducting magnet, to form the environment necessary for the microwave power generation. The use of high-temperature superconductor (HTS) material for a liquid cryogen-free gyrotron magnet will significantly reduce the input power requirements for the cryocooler compressor and the overall size of the magnet system. Cryomagnetics has designed, built and successfully tested a magnet wound with BSCCO-2223 tape to be used in the gyrotron. The HTS magnet was designed such that it can replace the current LTS (NbTi) cryogen-free gyrotron magnet in form, fit and function. The HTS magnet consists of 11 double-pancakes and provides stable 3.57 T operation at 37 K with a current of 120 A. Magnetic field shape, which is extremely important in gyrotron applications, was a considerable challenge since NbTi operating at 4.2 K is capable of a much higher current density than BSCCO operating at 37 K. Overall refrigeration requirements were reduced from ∼8 kW in the LTS system to ∼4 kW in the HTS system. A single-stage GM cryocooler was used to cool the HTS magnet. Comprehensive tests of the HTS magnet, including operation with the gyrotron tube, have been successfully completed.