Y. Hasegawa

University of Tsukuba, Tsukuba, Ibaraki, Japan

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Publications (2)3.62 Total impact

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    ABSTRACT: In order to understand the behavior of neutral hydrogen in ICRH plasmas of the GAMMA 10 tandem mirror, we tried new simulations of neutral transport by using the DEGAS Monte Carlo code in which the effects of hydrogen recycling were taken into account. This simulation has been performed by introducing a multiplication coefficient in DEGAS to control the amount of desorbed test particles, which enables us to simulate the neutral transport for the first time under the conditions in which the recycling coefficient exceeds unity. By using the multiplication coefficient, it was found that the axial profile of the atomic hydrogen density obtained from the simulation changed significantly. On the other hand, there is little influence on the radial profile of the simulated hydrogen density. The simulation result, taking the axial variation of the multiplication coefficient into consideration, well predicted the result of the Hα-emission measurements. This indicates that strong hydrogen recycling is localized near the midplane. These calculation results are discussed from the view point of the wall-reflux coefficient deduced from the DEGAS simulation.
    Journal of Nuclear Materials 01/1999; · 2.02 Impact Factor
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    ABSTRACT: Charge-exchange (C–X) neutral particle measurements have been carried out in hot-ion-mode plasmas of the GAMMA 10 tandem mirror. In the present experiment, a microwave power of 40 kW in 28 GHz is injected toward a second harmonic ECR layer located in the vicinity of the ICR layer at the central region and the radial profiles of ion temperatures determined from the energy spectrum of the C–X neutrals by using a neutral particle energy analyzer (NPA) are investigated from the viewpoint of ion energy balance. At the onset of the ECRH pulse, a remarkable increase of C–X neutral flux with high energy (few keV to few tens keV) is observed with NPA and the resultant ion temperature on the plasma axis is found to increase from 2.5 to 5.0 keV at the electron line density of 3 × 1013 cm – 2. Based on the measured plasma parameters, radial profiles of ion-energy losses due to classical processes are evaluated and ECRH in the central region is confirmed to reduce the energy loss due to electron drag significantly in the core-plasma region.
    Review of Scientific Instruments 01/1999; · 1.60 Impact Factor