Superconducting magnet control system of the JT-60SA

The JT-60U is being upgraded to a full-superconducting tokamak referred as the JT-60 Super Advanced (JT-60SA) as one of the JA-EU broader approach projects. JT-60SA will use superconducting magnets to confine the plasma and achieve a plasma current with flat top durations of up to 100 seconds. JT-60SA magnets are cooled by a helium refrigerator, whereby the local flow control is done by a "magnet controller". During cool down of the JT-60SA, the TF winding pack(WP) and the TF case are connected in series. Since the winding packs of the TF coils (TFWP) has rather high pressure loss, part of the helium flow from the refrigerator needs to bypass them and supplies directly the TF cases and support structures. The magnet controller controls the distribution of the flow. During nominal operation, 876g/s helium are supplied to the TFWP, which is too large for TF case. By introducing a bypass valve for TF case, about 0.1 MPa pressure loss can be saved. Finally the magnet controller has to react on off-normal situations for fail safe operation.