A Prototype Superconducting Magnet for 170 GHz Gyrotrons

In the frame of ITER program a prototype superconducting magnet for 170 GHz Gyrotrons was designed, manufactured and tested. The operating field (7.17 T in the center of 219 mm cold bore and 8.1 T at the winding) corresponds to a current of 183.5 A. In the final version of the magnet design the operating field was reached without any training. A specific field distribution along the axis was required with sharp decrease from both sides along the axis. Due to large axial forces a special support structure was used. The subcoils were wound from both $ Nb_3 Sn$ and NbTi multifilamentary graded wires. For quench protection the subcoils were shunted with 16 resistive shunts. A quench transformer type energy extraction system was also implemented in the magnet design. During the tests mechanical disturbances in the subcoils and support structure were observed.