Development of Measuring System of Density and Velocity Distribution Function of Atomic Hydrogen in the Edge Region of High-Temperature Plasmas

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It has by now been well recognized that understanding of particle behavior, in particular atomic hydrogen behavior, is prerequisite for effective density control and long-time maintenance of high-temperature plasmas. For this purpose, the above investigators proposed to develop a technique of the laser-induced fluorescence (LIF) using the two-photon excitation. The scheme is to excite atomic hydrogen from its ground leved (n=1) to n=3 or n=4 using powerful Raman-shifted ArF laser light, and the resultant fluorescence at Balmer transitions is to be detected. By the two-year-project, the following results have been obtained.(1) Among the possible excitation schemes for the two-photon excitation using ArF laser and its Raman shifted lights, namely (a) (205*2) nm, (b) (193+219) nm, and (c) (193+195) nm, the best scheme was experimentally and theoretically assessed. Here, the light at 205 nm was obtained by the first Stokes conversion and that at 219 nm by the second Stokes conversion of th … More e ArF laser in D_2 gas, and that at 195 nm by the rotational Raman shifting of the ArF laser in H_2 gas. For this reason, (a) and (b) are operative at the same time, and the obtainable signal from the both processes are 10 times larger than for (c). Therefore, we conclude that the combination (a) and (b) to be the best scheme for the purpose.(2) Using the titration process, we calibrated the system, yielding the measurement error of atomic hydrogen density to be within <plus-minus>20(3) By measuring fluorescence signals along the laser beam path when the laser was focused, we estimated the laser beam size, yielding better estimate of the signal intensity when the scheme is to be applied to actual measurements in high-temperature plasmas.(4) Based upon the above results, we estimated obtainable SN ratios for an envisaged optical system on JFT-2M.(5) Atomic hydrogen beheviour was also thoroughly investigated using the analysis technique developed by the investigators'group. Then, detailed database has been accumulated for diffusion coefficients and particle confinement time. Less