H. Yamada et al.


Density Limit in Discharges with High Internal Inductance on JT-60U

Date of publication:

Oct. 2006

Key words:

21 IAEA Fusion Energy Conference , EX/P8-8


High densities exceeding the Greenwald limit by a factor of 1.7 have been obtained in discharges withhigh internal inductances s of li as high as 2.8 in JT-60U. The internal inductance is controlled by rampingdown the plasma current. In addition to the extension of the operational regime limited by disruptions,confinement performance remains as good as an H89PL factor of 1.5 beyond the Greenwald limit. While theearlier work of a high li study has indicated that core confinement improvement due to enhancement of thepoloidal field, the additional improvement of the tolerance against the high density is turned out to be correlatedwith high edge temperature. The normalized density when the detachment characterized by the decrease in a D alpha signal at the divertor occurs is even higher in the case with no disruption compared with the case with adisruption. These comparisons have indicated that the improvement in thermal and particle transport does existin the periphery and the edge in the high li plasmas, and mitigation of the density limit is observedcoincidently. Although the high li discharge studied here lies outside of the usual parameter space for asteady-state operation of tokamak, demonstration of a stable discharge with good confinement beyond theGreenwald limit suggest the magnetic shear at the edge is one key parameter to uncover its physical element.

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