Two-dimensional distribution of divertor radiation in JT-60U

Two-dimensional (2D) reconstruction software was developed for bolometer signals of the JT-60U tokamak. Radiative divertor plasma with emissivity of 10 MW m−3 was found previously to extend 10 cm from the target plates. When the density is increased further by larger gas puffing, the emissivity imbalance between both divertor legs becomes less significant. The radiative zones move upward along the divertor legs and eventually merge into a single bright peak near the X-point at density around 6×1019 m−3 called X-point multifaceted asymmetric radiation from edge. Upward movement of the radiation peak during detachment is sometimes observed directly by the in-vessel bolometer. Total radiated power at the divertor saturates at a certain level while the core radiation continues to increase with the density. Although the 2D profile of the divertor radiation undergoes dramatic changes near the saturation, the energy confinement appears to degrade with density increase irrespective of these changes.