RADIATIVE DIVERTOR IN JT-60U

Characteristics of the divertor radiation loss are investigated with the spatially resolved bolometer arrays. In discharges with the ion grad-B drift toward the divertor, a radiative region is formed between the outer separatrix strike zone and the X-point. This radiative state is accompanied by a gradual decrease in heat flux to the divertor plates, and lasts for a few seconds with large particle fluxes to the separatrix strike zones, finally leading to a MARFE at the X-point. The radiation loss fraction of the input power depends on the electron density, NE heating power and safety factor, and can reach the level of radiation loss found in the MARFE. In the discharges with the ion grad-B drift away from the divertor, the MARFE has never been generated at the X-point. However, there is no significant difference in the maximum radiation loss level. The radiation loss is nearly in-out symmetric when the radiation loss is large for both types of discharges.