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Colorimetry in Nuclear Fusion Research
No full text0000-0001-5522-3082Colorimetry is a unique technique among research fields. The technique is also utilized in nuclear fusion research. The motivation is to evaluate the wide range of distribution of the deposition layer on the surface of the vacuum vessel. The deposition layer affects the control of fuel particles. Therefore, the result from colorimetry can contribute to the study of particle control in fusion plasma. In a particle control study, global particle balance analysis is usually conducted. Also, long-term samples irradiated by plasma have been analyzed. Colorimetry has the role of a bridge between these analyses. In this chapter, a demonstration of colorimetry in fusion devices is introduced.boo
Impact of Geodesic Curvature on Zonal Flow Generation in Magnetically Confined Plasmas
Get PDF0000-0003-2693-4859The impact of magnetic geometry on zonal-flow generation in ion temperature gradient driven turbulence is investigated by means of linear and nonlinear gyrokinetic simulations. The modulation of geodesic curvature on various configurations has revealed amplification of the zonal-flow intensity in relatively smaller geodesic curvature. Based on these findings, a nonlinear proxy model for explorations of novel magnetic geometry to activate the zonal-flow dynamics is proposed.journal articl
Analysis of Azimuthal Doppler Shift of Anisotropically Absorbed Laguerre-Gaussian Beam Propagating in Transverse Flow
Get PDF0000-0002-1583-3094The particle flux onto a material is an important parameter in the study of the plasma-material interaction. With conventional Doppler spectroscopy, it is difficult to measure the flow velocity perpendicular to the material because only the velocity component projected on the wave number vector can be measured. To overcome the limitation, we are developing a transverse flow measurement method using the azimuthal Doppler shift of a Laguerre-Gaussian (LG) beam absorption spectroscopy. In this paper, the feasibility of this spectroscopy method has been examined by numerical analysis. The LG beam is anisotropically absorbed in the transverse flow due to the azimuthal Doppler shift. Since the anisotropic LG beam rotates with propagation, the spatial structure of resonance absorption in plasma and the intensity structure of the LG beam that has propagated through the plasma are inevitably different in the LG beam absorption spectroscopy. It was shown that the deviation from the original azimuthal Doppler shift is reduced to several percent at the position where the intensity distribution of the LG beam reaches its maximum value. Therefore, the transverse flow can be measured with sufficient accuracy by properly selecting the position on the beam cross-section used to evaluate the azimuthal Doppler shift.journal articl
Onset of instability with collapse observed in relatively high density and medium beta regions of LHD
Get PDF0000-0003-3754-897XEdge MHD instabilities with pressure collapse are found in relatively high beta and low magnetic Reynolds number regions with a magnetic axis torus outward-shifted configuration of the large helical device (LHD), and characteristics and onset conditions of the instability are investigated. The instability has a radial structure with an odd parity around the resonant surface, which is different from that of the interchange instability typically observed in the LHD. The onset condition dependence on the magnetic axis location shows that the onset beta increases as the magnetic axis location moves more torus inwardly, and the instability appears only in limited configurations where the magnetic axis is located between 3.65 and 3.775 m. In such configurations, the resonant surface location is close to an index of the plasma boundary. This fact suggests that the distance between the resonant surface location and the plasma boundary plays an important role in the onset, and a possibility that the instability is driven by an external mode.journal articl
Spatiotemporal dynamics of high-wavenumber turbulence in a basic laboratory plasma
Get PDF0000-0002-5222-6082High-spatial resolution observation of high-wavenumber broadband turbulence is achieved by controlling the magnetic field to be relatively low and measuring with a azimuthally arranged multi-channel Langmuir array in a basic laboratory plasma. The observed turbulence consists of narrowband low-frequency fluctuations and broadband high-frequency turbulent fluctuations. The low-frequency fluctuations have a frequency of about 0.7 times the ion cyclotron frequency and a spatial scale of 1/10 of the ion inertial scale. In comparison, high-frequency fluctuations have a higher frequency than the ion cyclotron frequency and spatial scales of 1/10–1/40 of the ion inertial scale. Two-dimensional correlation analysis evaluates the spatial and temporal correlation lengths and reveals that the high-wavenumber broadband fluctuations have turbulent characteristics. The measurements give us further understanding of small scale turbulence in space and fusion plasmas.journal articl
超伝導コイルの循環冷却技術
Get PDFFocusing on the circulating cooling of superconducting coils, the author introduces an example of research and development that cools the coil by circulating liquid helium, gas helium, and liquid hydrogen. In order to realize more efficient cooling, the author explains a method that combines a circulation method with magnetic refrigeration and oscillating heat pipes, and a method that involves circulation with a cryofan in the state of low temperature fluid without going through room temperature. In addition, the benefits of circulating cooling are also mentioned.journal articl
新しい時代の核融合科学研究所
Get PDF核融合研究は新しい時代を迎えようとしている．その変化に対応するため，いやむしろ変化を先導するために，核融合研（NIFS）は大きな改革を行う．広い学術界の期待を担える共同研究機関として，生まれ変わる．２０２１年度から，コミュニティーをあげて行っている議論の中間まとめをここに記録し，これからどのような変化を起こそうとしているのかを述べて，より広く深いコミュニケーションを喚起したい．othe
Relations among Turbulent Fluctuations, Zonal Flows, and Transport Coefficients in Time Series Data of Gyrokinetic Simulations
Get PDFThe relations among turbulent amplitude, zonal-flow amplitude, and transport level are discussed for the time series data of nonlinear gyrokinetic simulations for magnetized toroidal plasmas. Since it was shown that the transport coefficient can be expressed as a function of the time-averaged turbulent fluctuation level and the zonal flow amplitude [M. Nunami et al., Phys. Plasmas 20, 092307 (2013)], we apply the results to a model function for the turbulent plasma transport coefficient to extend to a functional relation which includes not the time-averaged data but the time-series data of gyrokinetic simulations. We obtain a new functional relation to the turbulent fluctuations, the zonal-flow amplitudes, and the transport coefficients as a function of the input parameters of the gyrokinetic simulations such as plasma temperature gradients. It is also confirmed that the obtained functional relation can reduce relative error which is compared with the original function with time-averages.journal articl
Nonlinear functional relation covering near- and far-marginal stability in ion temperature gradient driven turbulence
Get PDF0000-0002-6719-9013A novel nonlinear functional relation of turbulence potential intensity, zonal flow potential intensity, and ion thermal diffusivity that accurately reproduces nonlinear gyrokinetic simulations of toroidal ion temperature gradient (ITG) driven turbulence is proposed. Applying mathematical optimization techniques to find extremal solutions in high-dimensional parameter space, the optimal regression parameters in the functional form are determined to be valid for both near- and far-marginal regime of the ITG stability including the Dimits-shift. Then, the regression error of ∼5% is accomplished. In addition, it is clarified that the intensity ratio of the zonal flow and turbulence potential intensity is a crucial factor to determine the reproduction accuracy.journal articl
Prediction of temperature profiles in helical plasmas by integrated code coupled with gyrokinetic transport models
Get PDF0000-0002-0712-8811Transport simulation is performed by integrated code using reduced transport models (Toda S et al 2019 Phys. Plasmas 26 012510) in a kinetic electron condition for turbulent heat transport including the effect of zonal flows in helical plasmas. A reduced model can be formulated for the heat diffusivity using only the linear properties, or can be constructed by considering the expression of the quasilinear flux. These reduced models reproduce nonlinear gyrokinetic simulation results for ion temperature gradient mode turbulence by a linear growth rate and zonal flow decay time. Temperature profiles can be obtained when the turbulent heat transport is evaluated by reduced models at each time step in the evolution of integrated simulation. Computational cost using the reduced models where linear gyrokinetic simulation is performed at each time step in the integrated simulation is about two orders of magnitude lower than that using nonlinear gyrokinetic simulation. Stationary temperature profiles are predicted by simulation, in which, the linear simulation is performed at each time step in the integrated simulation for steady heating power. The density profile and the edge temperature are needed in this simulation.journal articl