Characteristics of halo currents in JT-60U

Halo currents (Ih) and their toroidal peaking factors (TPFs) have been measured in JT-60U by Rogowski coil type halo current sensors. The maximum value of TPF x Ih/Ip0 was 0.52 in the operational range of Ip0 = 0.7-1.8 MA, BT = 2.2-3.5 T, including ITER design parameters of k > 1.6 and q95 = 3, which was lower than that of the maximum value of the ITER database (0.75). This value of TPF x Ih/Ip0 correlated with the driving forces of the halo currents generated by the vertical shift velocity of the plasma. The magnitude of the halo currents tended to decrease with the increase in stored energy just before the energy quench and with the line integrated electron density at the time of maximum halo current. A termination technique in which the current channel remains stationary demonstrated how to avoid halo current generation. Strong pulsed gas puffing during vertical displacement events was effective in reducing the halo currents. (author)