Development of reversed shear plasmas with high bootstrap current fraction towards reactor relevant regime in JT-60U

This paper reports the recent development of reversed shear plasmas with a high bootstrap current fraction (fBS) towards the reactor relevant regime. The previous operation regime of high fBS plasmas is limited at q95 > 8 because of the low beta limit, whereas q95 = 5-6 is envisaged in the DEMO reactor. In the 2008 JT-60U experimental campaign, the high fBS plasma was emphasized in the lower q95 regime by developing the large volume configuration close to the conducting wall for wall stabilization. Thanks to the wall stabilization, high fBS plasmas exceeding the no-wall beta limit are obtained at reactor relevant q95 ∼ 5.3. Though the high fBS plasmas are terminated by destabilization of the resistive wall mode, a highly integrated performance is obtained. High values of HH98y2 ∼ 1.7, βN ∼ 2.7, fBS ∼ 0.92 and ne/nGW ∼ 0.87 are simultaneously achieved under the reactor relevant conditions of low momentum input and electron temperature nearly equal to ion temperature.