We have recently incorporated the occupation probability formalism (OPF) in the simulation model C. Stehlé and S. Jacquemot, Astron. Astrophys. 271, 348 (1993) to have a smooth transition from ...discrete lines to continuum spectrum in the wavelength range near the Balmer series limit. We have analyzed spectra measured for the hydrogen pellet ablation cloud in the Large Helical Device with the revised model, and have found that the electron density in the ablation cloud has a close correlation with the electron temperature of the background plasma. This type of correlation is first confirmed in the present analysis and should give a new insight in the simulation studies of pellet ablation for the magnetically confined fusion plasma.
The ergodic layer in the Large Helical Device (LHD) consists of stochastic magnetic fields exhibiting a three-dimensional structure that is intrinsically formed by helical coils. Spectroscopic ...diagnostics was employed in the extreme ultraviolet (EUV) and vacuum ultraviolet (VUV) wavelength ranges to investigate emission lines of carbon impurities in both hydrogen (H) and deuterium (D) plasmas, aiming to elucidate the impact of distinct bulk ions on impurity generation and transport in the edge plasmas of the LHD. The emission intensity of carbon CIII, CIV, CV, and CVI lines is significantly higher in the D plasma compared to the H plasma, indicating a greater sputtering rate of carbon materials in the D plasma, resulting in a higher quantity of carbon impurities originating from the divertor plates. A Doppler profile measurement of the second order of CIV line emission (1548.20 × 2 Å) was attempted using a 3 m normal-incidence VUV spectrometer in the edge plasma at a horizontally elongated plasma position. The flow velocity reaches its maximum value close to the outermost region of the ergodic layer, and the observed flow direction aligns with the friction force in the parallel momentum balance. The flow velocity increases with the electron density in H plasmas, suggesting that the friction force becomes more dominant in the force balance at higher density regimes. This leads to an increase in the impurity flow, which can contribute to the impurity screening. In contrast, the flow velocity in the D plasma is smaller than that in the H plasma. The difference in flow values between D and H plasmas, when the friction force term dominates in the momentum balance, could be attributed to the mass dependence of the thermal velocity of the bulk ions.
Abstract
An infrared spectro-polarimeter installed on the Solar Flare Telescope at the Mitaka headquarters of the National Astronomical Observatory of Japan is described. The new spectro-polarimeter ...observes the full Sun via slit scans performed at two wavelength bands, one near 1565 nm for a Zeeman-sensitive spectral line of Fe i and the other near 1083 nm for He i and Si i lines. The full Stokes profiles are recorded; the Fe i and Si i lines give information on photospheric vector magnetic fields, and the helium line is suitable for deriving chromospheric magnetic fields. The infrared detector we are using is an InGaAs camera with 640 × 512 pixels and a read-out speed of 90 frames s−1. The solar disk is covered by two swaths (the northern and southern hemispheres) of 640 pixels each. The final magnetic maps are made of 1200 × 1200 pixels with a pixel size of $1{^{\prime\prime}_{.}}8$. We have been carrying out regular observations since 2010 April, and have provided full-disk, full-Stokes maps, at the rate of a few maps per day, on the internet.
Polarization of the hydrogen Lyman-α line is detected in the Large Helical Device. It is the first observation of a polarized atomic emission line in magnetically confined fusion plasma devices. With ...the help of an atomic model simulation, the anisotropy in the electron velocity distribution function (EVDF) in terms of T∥/T⊥ is evaluated, where T∥ and T⊥ represent the electron temperature in the parallel and perpendicular directions regarding the magnetic field, respectively. The results show that T∥/T⊥ has a tendency to decrease and deviate from unity with decreasing electron-electron collision frequency, which qualitatively agrees with an intuitive understanding of the anisotropic EVDF in the plasma boundary.
High precision measurements and accurate modeling of atomic polarization under three-dimensional radiation transfer are crucial to understand the structures of magnetized solar plasmas. To develop ...and validate spectropolarimetric measurements and analyses, we set up an inductively coupled plasma (ICP) generator designed especially for ∼1-eV plasmas interacting with radiation and weak magnetic fields. The device was put in front of the focal plane of the Horizontal Spectrograph of the Domeless Solar Telescope at Hida Observatory of Kyoto University. In helium discharges, the typical electron temperature, electron density, and helium column density of the ICP are comparable values to those of solar prominences, and the direct comparison of spectra shows almost the same opacity at He I 1083 nm. Magnetic and radiation fields were introduced to the ICP, and the system successfully reproduced reasonable spectropolarimetric signals as compared with those from the solar prominences.
Perspective of Meta-Hierarchy Dynamics NUNAMI, Masanori; ITO, Atsushi M.; GOTO, Motoshi ...
Plasma and Fusion Research,
07/2023, Letnik:
18
Journal Article
Recenzirano
Odprti dostop
The understanding of nature has been developed by separating and connecting elements in a reductive manner. For example, a spatio-temporal scale can provide us a clear picture of elemental ...separations. In biology, a function also gives us a useful picture to understand biological nature. Furthermore, a physical model also improves the outlook for understanding physical nature. These divided or connected elements, namely, scales, functions, and models form hierarchical structures in nature. On the other hand, fusion science explores various multi-scale and multi-physics phenomena, spreading over spatio-temporal scales from the microscopic to the macroscopic. In particular, collective motion causes structural formations not only in core plasmas but also material-facing ones. Therefore, fusion science has been an excellent subject for the application of the hierarchical approach. However, some problems have emerged with the progress of experimental and numerical research in fusion science. We often encounter phenomena that cannot be well understood by hierarchical separation. For these phenomena, beyond the conventional approaches for hierarchical systems, it is necessary to reconsider them with meta-perspectives, i.e., meta-hierarchy dynamics.
In the Large Helical Device, the divertor detachment has been attempted by application of resonant magnetic perturbation (RMP) field and Ne gas puffing in electron cyclotron resonance- heated ...discharges for compatibility of high central electron temperature and low divertor heat load. Two kinds of divertor detachment phases were observed. The first one appeared transiently just after the Ne gas puffing (1st detachment), and the second one appeared steadily in the latter half of the discharge (2nd detachment). Space-resolved extreme ultraviolet spectroscopy revealed that NeVI-NeVIII emissions increased slightly outside the last closed flux surface (LCFS), while NeIX and NeX emissions increased inside the LCFS in the 1st detachment phase. Although in the 1st detachment the divertor heat load was significantly reduced, the central electron temperature also decreased because the Ne ions were penetrated inside the LCFS as a radiation source. In the 2nd detachment phase, NeVINeVIII emissions increased outside the LCFS while NeIX and NeX emissions kept low intensity inside the LCFS. In this phase, low divertor heat load and high central electron temperature were obtained simultaneously because the Ne ions were localized outside the LCFS as a radiation source. The profile measurements of Ne emission show that the edge island structure created by the RMP application impacts on the impurity emission distribution, where the peak of the emission shifts radially stepwise as the detachment proceeds.
The National Institute for Fusion Science (NIFS) has compiled and developed atomic and molecular numerical databases for various collision processes and makes it accessible from the internet to the ...public. The database contains numerical data of cross sections and rate coefficients for electron collision or ion collisions with atoms and molecules, attached with bibliographic information on their data sources. The database system provides query forms to search data, and numerical data are retrievable. The graphical output is helpful to understand energy dependence of cross sections and temperature dependence of rate coefficients obtained by various studies. All data are compiled mainly from published literature, and data sources can be tracked by the bibliographic information. We also have data of sputtering yields and back-scattering coefficients for solid surfaces collided by ions in the database. All data in the database are applicable to understand atomic and molecular processes in various plasmas, such as fusion plasma, astrophysical plasma and applied plasma, as well as for understanding plasma–surface interaction in plasmas.
Spectroscopic studies for emissions released from tungsten ions have been conducted in the Large Helical Device (LHD) for contribution to the tungsten transport study in tungsten divertor fusion ...devices and for expansion of the experimental database of tungsten line emissions. Tungsten ions are distributed in the LHD plasma by injecting a pellet consisting of a small piece of tungsten metal wire enclosed by a carbon tube. Line emissions from W0, W5+, W6+, W24+–W28+, W37+, W38+, and W41+–W46+ are observed simultaneously in the visible (3200–3550 Å), vacuum ultraviolet (250–1050 Å), and extreme ultraviolet (5–300 Å) wavelength ranges and the wavelengths are summarized. Temporal evolutions of line emissions from these charge states are compared for comprehensive understanding of tungsten impurity behavior in a single discharge. The charge distribution of tungsten ions strongly depends on the electron temperature. Measurements of emissions from W10+ to W20+ are still insufficient, which is addressed as a future task.
The intensity ratio of Fe XIV 264.765A/274.203A is useful to determine the electron density of solar corona, and the relationship between the electron density and the intensity ratio obtained from a ...model should be evaluated using laboratory plasmas to estimate the electron density more precisely. We constructed a new collisional–radiative model (CR-model) for Fe XIV (an Al-like iron ion) by considering the processes of proton-impact excitation and electron-impact ionization to the excited states of a Mg-like iron ion. The atomic data used in the CR-model were calculated using the HULLAC atomic code. The model was evaluated based on laboratory experiments using a compact electron beam ion trap, called CoBIT, and the Large Helical Device (LHD). The measured Fe XIV 264.785 Å/274.203 Å line intensity ratio with CoBIT was 1.869 ± 0.036, and it agreed well with our CR-model results. Concurrently, the measured ratio using LHD was larger than the results of our CR-model and CHIANTI. The estimated electron densities using our CR-model agreed with those from CHIANTI within a factor of 1.6–2.4 in the range of ne≈1010−11cm−3. Further model development is needed to explain the ratio in a high-electron density region.
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