In the axisymmetrized tandem mirror GAMMA 10, thermal-barrier and plug potentials have been formed in the axisymmetric mirror cells at both ends and directly measured with Au neutralbeam probes and end-loss analyzers. Strong end-loss reduction associated with the potential formation results in enhancement of the axial particle confinement time 100 times over the mirror confinement time without plugging, in reasonable agreement with Pastukhov formula. An empirical scaling on nonambipolar radial ion confinement time in the axisymmetrized field configuration is presented.PACS numbers: 52.55.Jd Current tandem mirror researches focus on improvement of confinement properties over the original configuration.

To inspect the post-accident nuclear core reactor of the TEPCO Fukushima Daiichi nuclear power plant (F1-NPP), a transportable fiber-coupled laser-induced breakdown spectroscopy (LIBS) instrument has been developed. The developed LIBS instrument was designed to analyze underwater samples in a highradiation field by single-pulse breakdown with gas flow or double-pulse breakdown. To check the feasibility of the assembled fiber-coupled LIBS instrument for the analysis of debris material (mixture of the fuel core, fuel cladding, construction material and so on) in the F1-NPP, we investigated the influence of the radiation dose on the optical transmittance of the laser delivery fiber, compared data quality among various LIBS techniques for an underwater sample and studied the feasibility of the fiber-coupled LIBS system in an analysis of the underwater sample of the simulated debris in F1-NPP. In a feasible study conducted by using simulated debris, which was a mixture of CeO 2 (surrogate of UO 2 ), ZrO 2 and Fe, we selected atomic lines suitable for the analysis of materials, and prepared calibration curves for the component elements. The feasible study has guaranteed that the developed fiber-coupled LIBS system is applicable for analyzing the debris materials in the F1-NPP.

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