Sustainment of high confinement in JT-60U reversed shear plasmas

Experimental results towards long sustainment of JT-60U reversed shear (RS) plasmas, where high confinement is achieved owing to strong internal transport barriers, are reported. In a high current plasma with an L mode edge, a deuterium-tritium-equivalent fusion power gain Q DT eq = 0.5 was sustained for 0.8 s (≈the energy confinement time) by precise adjustment of the plasma beta using feedback control of stored energy. In a high triangularity plasma with an ELMy H mode edge, a high bootstrap current fraction (≈80%) was obtained in a high q regime ( q 95 ≈9), which led to the full non-inductive current drive condition. A normalized beta β N ≈2 and an H factor H 89 ≈3.5 ( HH 98 y 2 ≈2.2) were sustained for 2.7 s (about 6 times the energy confinement time). The values of β N and H 89 sustained in RS plasmas were improved remarkably by operating with high bootstrap current fraction and high triangularity.