Spatial distribution measurement of atomic radiation with an astigmatism-corrected Czerny-Turner-type spectrometer in the Large Helical Device

Emission lines in the visible/UV wavelength ranges are observed with 80 lines of sight which cover an entire poloidal cross section of the plasma in the Large Helical Device. The emitted light is received with optical fibers having 100 ?m diameter and is guided into a 1.33 m Czerny-Turner-type spectrometer based on spherical mirrors for collimating and focusing. A charge-coupled device having 13.3×13.3 mm^2 area size is used as the detector and the spectra from all the lines of sight are recorded perpendicularly to the wavelength dispersion. The spectrometer is equipped with optics located in front of the entrance slit to correct the difference between the meridional and sagittal focal points, and thus the astigmatism, which otherwise causes severe cross talk between adjacent optical fiber images on the detector, is corrected. Consequently, simultaneous spectral measurement with 80 lines of sight is realized. The Zeeman splitting of a neutral helium line, lambda667.8 nm (2 ^1P-3 ^1D), which is caused by the magnetic field for plasma confinement, is measured with the spectrometer. Though the obtained line profile is in general a superposition of several components on the same line of sight, they can be separated according to their different splitting widths. The two-dimensional poloidal distribution of the helium line intensity is obtained with the help of a tomographic technique

Poloidal Distribution Measurement of Inward Neutral Flux in LHD

Three emission lines of neutral helium, i.e., the λ 667.8 nm (21P-31D), λ 728.1 nm (21P-31S), and λ 706.5 nm (23P-33S) lines, are observed with an array of parallel lines-of-sight which covers an entire poloidal cross section of the plasma in the Large Helical Device (LHD). Their emission locations and intensities are determined from the Zeeman profiles. The electron temperature and density are evaluated from intensity ratios among the observed emission lines at each emission location and the poloidal distribution of ionization flux or its equivalent quantity, inward neutral particle flux, is derived with the help of collisional-radiative model calculations. A relatively strong neutral flux is observed at the inboard-side X-point and this result implies a high particle recycling in the inboardside divertor region. The result is consistent with the ion flux distribution onto the helically located divertor plates measured with Langmuir probes

Relations between the ionization or recombination flux and the emission radiation for hydrogen and helium in plasma

On the basis of the collisional-radiative models for neutral hydrogen, and neutral and ionized helium, the relationship between the ionization flux or the recombination flux and the photon emission rate of a representative visible line of each species is investigated. It is found that both fluxes are proportional to the photon emission rate and that the proportionality factor depends rather weakly on the plasma parameters in the ranges of practical interest. This implies that the observed emission line intensity can be a good measure of the ionization flux or the recombination flux. The relation between the total radiation power rate and the ionization or recombination flux is also considered. For a hydrogen plasma in ionization balance the Balmer-alpha line intensity takes the maximum value near the optimum temperature of 1.3 eV, while for plasmas out of ionization balance it takes the minimum near that temperature. This latter characteristic corresponds to the recently observed "inverse edge-localized mode" in divertor plasmas. For neutral hydrogen and ionized helium, it is found that in the recombining plasma of low electron temperature, T_e, and density, n_e, the radiation energy close to the ionization potential of the ground state is emitted during one recombination event. In the ionizing plasma of high Te and low n_e, a similar amount of energy is emitted during one ionization event. Emission line intensities of hydrogen and helium were measured in the Large Helical Device, and the time variation of n_e at the initial and final phases of a discharge was estimated. The results agreed well with the interferometer measurement, and this indicated that the variation of n_e was dominated by their ionization or recombination processes rather than by diffusion. The total radiation energy of hydrogen and helium in the recombining phase was found to be less than 1% of the stored energy of the plasma

チテキカンキョウニオケルインタラクションシエンノタメノジッセカイコンテキストニンシキオヨビオウヨウ

We have observed Fe14+ (3s^2 ^1S_0 - 3s3p ^1P_1) and Fe15+ (3s ^2S1/2 - 3p ^2P_[3/2]) emissions from a LHD plasma with a space-resolved extreme-ultraviolet spectrometer. The observed intensity distributions against the viewing chord for the respective emissions are reconstructed to the emission flux distributions in the plasma against the normalized radius of the poloidal cross section with a maximum entropy method. Both of the emissions localize in the periphery region, and the Fe^[14+] emission is located outer side than that of Fe15+. We calculate the charge state distribution of Fe ions against the normalized radius assuming the ionization equilibrium at the electron temperature and density, which are measured by a Thomson scattering method. The calculated result is consistent with the experimental one

Properties of OV Spectral Lines in Ionizing and Recombining Plasmas

A collisional-radiative model for Be-like oxygen ions has been constructed for OV plasmaspectroscopy. The model takes into account recombination processes as well as collisional ionization, radiative transitions, and collisional excitation/deexcitation. Two sets of atomic data are used for comparison. We obtain OV line intensities as functions of electron temperature and density. The line intensity ratios of 2s3s 35 - 2s3p \u27Pr=o.r., are measured in LHD plasmas and are consistent with our models. The line intensity ratio of 2s2p 3P - 2p"P and 2s2 tS - 2s2p rP in recombining plasma is an increasing function of temperature and one measured in the LHD plasma indicates electron temperature less than 7eV. The ratios measured in steady-state phase are larger than I and difficult to explain with the current model

Space-resolved visible spectroscopy for two-dimensional measurement of hydrogen and impurity emission spectra and of plasma flow in the edge stochastic layer of LHD

A space-resolved visible spectrometer system has been developed for two-dimensional (2D) distribution measurements of hydrogen and impurity emission spectra and of plasma flow in the edge stochastic layer of Large Helical Device (LHD). Astigmatism of the spectrometer has been suppressed by introducing additional toroidal and spherical mirrors. A good focal image at the exit slit is realized in a wide wavelength range (75 nm) as well as in a wide slit height direction (26 mm) with a 300 grooves/mm grating. The capability of the spectrometer optical system for the 2D measurement and further possible improvements are discussed in detail. An optical fiber array of 130 channels with a lens unit is used to spatially resolve the edge plasma into different magnetic field structure components: divertor strike points, divertor legs, X-point of the legs, the stochastic layer, and the last closed flux surface. With a 300 grooves/mm grating, the 2D distributions of several hydrogen and impurity line emissions are simultaneously obtained with absolute intensities. A clear correlation is obtained between the magnetic field structure and the emission intensity. With a 2400 grooves/mm grating with a good spectral resolution (0.03 nm/pixel), the 2D distributions of impurity flow velocity are obtained from the Doppler shift measurement. The wavelength position is accurately calibrated by investigating the wavelength dispersion as well as by correcting a mechanical error of the optical setting in the spectrometer. The uncertainty in the velocity is reduced to less than 10% of a typical impurity velocity ∼104 m/s. A temporal change in the flow directions is observed at different spatial locations in divertor detachment plasma