Magnetic field measurements of JT-60SA CS model coil

• Magnetic fields of the JT-60SA CS model coil were measured.
• While the coil current was held constant at 20 kA, magnetic fields varied slightly with several different long time constants.
• We investigated coils consisting of CIC conductors and having long time constants.

In a cold test of the JT-60SA CS model coil, which has a quad-pancake configuration consisting of a Nb3Sn cable-in-conduit (CIC) conductor, magnetic fields were measured using Hall sensors. For a holding coil current of 20 kA, measured magnetic fields varied slightly with long time constants in the range 17–571 s, which was much longer than the time constant derived from a measurement using a short straight sample. To validate the measurements, the magnetic fields of the model coil were calculated using a computational model representing the positions of Nb3Sn strands inside the CIC conductor. The calculated results were in good agreement with the measurements. Consequently, the validity of the magnetic field measurements was confirmed. Next, we investigated other coils consisting of CIC conductors and having long time constants. The only commonality among the coils was the use of CIC conductors. At present, there is no obvious way to prevent generation of such magnetic-field variations with long time constants.