H. Ozawa

H. Takeda

H. Zushi

K. Hosoi

M. Sakamoto

M." Shoji

R. Yonenaga

S. Kobayashi

T. Ishii

Y. "Nakashima

National Institute for Fusion Science (NIFS-Repository)

Investigation of behavior of neutral particle transport isimportant subject for evaluating particle and energytransport in torus plasmas. In particular, edge plasma –neutral interaction is much interesting subject from theviewpoint of long-lasting and steady state plasmaproduction. QUEST is a medium sized spherical tokamakdevice whose chamber height is 2.8 m and radius is 1.4 m.The diameter of the CS is 0.4 m. The major (R) and minorradii of the plasma are 0.68 m and 0.4 m, respectively.Eight toroidal field (TF) coils produce the toroidalmagnetic field, Bt ~0.25 T at R ~0.64 m. PF coils are usedto create the vertical field, Bv. The magnetic field forplasma confinement is optimized by adjusting the TF andPF. The plasma discharge is sustained using hydrogen gaspuffing and ECH by 8.2 GHz klystrons.Figure 1 shows the photograph of the horizontal viewingport of QUEST vacuum chamber and the image fibersystem with a medium-speed camera. This system consistsof two-branched image fiber, CCD camera (HAS-220,DITECT INC.) and relay lens. The object side of the fiberis separated, which enables to observe the different imageof the plasmas simultaneously. The frame speed of themedium-speed camera is 500 fps. An interference filter thattransmits 75% of light at wavelengths from 650 nm to 690nm is attached between the set of relay lens so that only Hα-light (656.3 nm) can be observed in the plasma. Thecamera is connected to a PC in the QUEST machine room.Two-dimensional images are captured during the QUESTexperiment just after the PC in the machine room receives atrigger signal, which is synchronized with the start-up ofthe coil current. The time evolution of the light-emissionfrom the QUEST plasma has been captured with the abovecamera system. Two-dimensional image of light–emissionwas measured mainly in RF produced plasmas.In order to develop a transport analysis of neutrals andimpurities, a standard configuration of plasma surface andplasma parameters are well clarified. Fig.2 shows theexample of magnetic surface calculated in QUEST. In thismodel, the plasma is in the condition just before obtaining adivertor configuration.We are preparing the application of the DEGAS code toQUEST in order to investigate the behavior of neutrals inthe spherical torus plasma. Figure 3 shows a example of themesh model. In this design, the shape of the plasma issimply modeled as a torus with the circular cross-section.After determination of optimized magnetic flux surface,detailed mesh structure will be made and the simulationanalyses will be started.1) H. Zushi, et al. 22th IAEA Fusion Energy Conf. EX/P4-12 (13-18 October 2008, Geneva, Switzerland).2) Y. Higashizono et al. Proc. 7th General ScientificAssembly of the Asia Plasma and Fusion Association,(October 27-30 2009,Aomori, Japan).Fig. 1  Photograph of the medium-speed cameraand imaging fiber system.Fig. 2  Example of magnetic surface of QUESTFig. 3  Mesh model of the QUEST vacuumchamber and plasma for the DEGAS code.534§56. Hydrogen Recycling and Neutral Particle and Impurity Behavior in Spherical Torus PlasmasNakashima, Y. (PRC, Univ. Tsukuba),  Kobayashi, S. (IAE, Kyoto Univ.),  Sakamoto, M., Zushi, H. (RIAM, Kyushu Univ.),  Yonenaga, R., Hosoi, K., Ozawa, H., Takeda, H.,  Ishii, T. (Graduate School of Pure and Appl. Sci., Univ. Tsukuba,),  Shoji, M.

Hydrogen Recycling and Neutral Particle and Impurity Behavior in Spherical Torus Plasmas

Hydrogen Recycling and Neutral Particle and Impurity Behavior in Spherical Torus Plasmas

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