A liquid-level sensor, consisting of three optical fibers, is described. A light is projected onto an oil surface through a transmitting fiber. A receiving fiber picks up the light reflected from the oil surface. A reference fiber transmits the light from a light-emitting diode back and forth along the same path as that of the transmitting fiber and the receiving fiber. Division is accomplished by using the reflected signal and the reference signal, so it becomes possible to eliminate apparent distance variations that are due to the variations in light intensity, which may be caused by external forces and temperature changes. The distance range is 100 mm.

First results of the two-dimensionally reconstructed distribution of divertor radiation in JT-60U are presented. Hardware improvements of in-vessel divertor bolometer cameras to withstand severe electrical and thermal loads and the development of tomography software have made detailed and visual studies of divertor radiation possible. Line-integrated bolometer signals are successfully mapped onto the JT-60U geometry, indicating characteristic profiles for radiative divertor operation. A unique measurement of the radiating layer width at the target plate independently confirms the results of tomographic analysis. Radiation which is almost uniformly distributed along the separatrix flux line from the inboard to the outboard divertor is identified in the moderate density H-mode. Temporal evolution of radiative collapse due to heavy argon radiation is explored. Difficulties in the reconstruction associated with the local hot spot and neutrals are also discussed.

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