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Report No.

Profile control and plasma start-up by RF waves towards advanced tokamak operation in JT-60U

Takase, Yuichi*; JT-60 Team

A central electron temperature of 23 keV was obtained by EC wave injection. A highly localized current density profile was obtained by central ECCD, indicating an upper limit on the diffusion coefficient for resonant electrons of $$1{rm m^{2}/s}$$. The experimentally obtained current drive figure of merit was lower than theoretical prediction, possibly because of the negative loop voltage induced by overdrive. A comparison of HFS and LFS off-axis ECCD confirmed the theoretically expected trapped particle effect on the current drive efficiency. Offaxis LHCD was used to broaden the qmin radius and the ITB foot radius. N-NBCD was used to shrink the current hole radius. An integrated scenario consisting of (1) a novel plasma start-up method using RF plasma production and induction by vertical field and shaping coils, (2) a noninductive ramp-up stage, and (3) a transition to a high-density, bootstrap-dominated, highconfinement plasma, without the use of the OH solenoid, has been demonstrated. The plasma created by this technique had both internal and edge transport barriers, with $$beta_{rm p}=3.6$$($$epsilonbeta_{rm p}=1$$), $$beta_{rm N}=1.6$$, $$H_{rm H98y2}=1.6$$ and $$f_{rm BS}geq90%$$ at $$I_{rm p}=0.6$$MA and $$n_{rm e}=0.5n_{rm GW}$$.



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