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 (f(BS)) towards the reactor relevant regime. The previous operation regime of high f(BS) plasmas is limited at q(95) > 8 because of the low beta limit, whereas q(95) = 5-6 is envisaged in the DEMO reactor. In the 2008 JT-60U experimental campaign, the high f(BS) plasma was emphasized in the lower q(95) regime by developing the large volume configuration close to the conducting wall for wall stabilization. Thanks to the wall stabilization, high f(BS) plasmas exceeding the no-wall beta limit are obtained at reactor relevant q(95) similar to 5.3. Though the high f(BS) plasmas are terminated by destabilization of the resistive wall mode, a highly integrated performance is obtained. High values of HH98y2 similar to 1.7, beta(N) similar to 2.7, f(BS) similar to 0.92 and n(e)/n(GW) similar to 0.87 are simultaneously achieved under the reactor relevant conditions of low momentum input and electron temperature nearly equal to ion temperature.