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 QDTeq = 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 (q95≈9), which led to the full non-inductive current drive condition. A normalized beta βN ≈2 and an H factor H89≈3.5 (HH98y2≈2.2) were sustained for 2.7 s (about 6 times the energy confinement time). The values of βN and H89 sustained in RS plasmas were improved remarkably by operating with high bootstrap current fraction and high triangularity.
High performance reversed shear plasmas with a large radius transport barrier in JT-60U
Overview of JT-60U results towards the establishment of advanced tokamak operation