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Spatially resolved rotational temperature of ground state hydrogen molecules desorbed from plasma-facing surface was measured in QUEST, LTX-β, and DIII-D tokamaks, and the increases of the rotational temperature with the surface temperature and due to collisional-radiative processes in the plasmas were evaluated. The increase due to collisional-radiative processes was calculated by solving rate equations considering electron and proton collisional excitation and deexcitation and spontaneous emission. The calculation results suggest a high sensitivity for the rotational temperature to electron and proton densities, but a negligible sensitivity to the electron, proton, and surface temperatures. In the three tokamaks with different plasma parameters and plasma facing surface materials, the spatial profile of the rotational temperature was estimated using Fulcher-α emission lines (600-608 nm). In QUEST, the spatial profile of the rotational temperature was estimated from spatially resolved spectra. In the other tokamaks, the rotational temperature was evaluated assuming a single point emission with a location determined from the Fulcher-α emission profile as measured with a filtered camera. In metal-walled devices QUEST and LTX-β, the rotational temperature increased with the surface temperature, and the calculated collisional-radiative increase is consistent with measured increase assuming that the rotational temperature at the surface is approximately 450 K higher than the surface temperature. In DIII-D with carbon walls, a larger collisional-radiative increase than the other tokamaks was observed because of the higher density leading to a large difference from the calculated increase compared to the other smaller tokamaks. Measurement of the Fulcher-α emission profile with higher spatial resolution in DIII-D may reduce the difference and reveal the effect of the surface temperature on the rotational temperature. These results shows the increases in the rotational temperature with the surface temperature and due to the collisional-radiative processes.

The first step to realize automatic experimental data analysis for fusion plasma experiments is fitting noisy data of temperature and density spatial profiles, which are obtained routinely. However, it has been difficult to construct algorithms that fit all the data without over- and under-fitting. In this paper, we show that this difficulty originates from the lack of knowledge of the probability distribution that the measurement data follow. We demonstrate the use of a machine learning technique to estimate the data distribution and to construct an optimal generative model. We show that the fitting algorithm based on the generative modeling outperforms classical heuristic methods in terms of the stability as well as the accuracy., Accepted by Transactions on Plasma Science

A spectroscopic system with multiple viewing chords was developed for QUEST (Q-shu University Experiment with Steady-State Spherical Tokamak) to measure the spatial distribution of ion toroidal velocities in discharges sustained by electron cyclotron resonance heating (ECH). Twenty-four viewing chords were aligned in the midplane and C III emission line spectra were measured for three types of ECH discharge under different magnetic field configurations. By applying an inversion method to the measured spectra, we evaluated the radial distributions of C2+ ion emissivity, temperature, and toroidal velocity. The error in the evaluated velocity was estimated to be less than 5 km/s. It was found that the velocity depends on the magnetic field configuration.

Photoluminescence (PL) spectra from diamond nanoparticles containing negative nitrogen vacancy centers were measured by using a single multimode fiber endoscope combined with a high-sensitivity spectroscopy system. A laser light spot was produced at the distal end of the endoscope and the PL spectra from a temperature-controlled ensemble of diamond nanoparticles were measured. After calibrating the sensitivity and wavelength of the spectroscopy system, the temperature dependence of the zero-phonon line peak wavelength similar to those previously reported was obtained.

Manual uncertainty propagation from possible noise sources has often been adopted for data analysis in many fields of science, including the analysis of Thomson scattering measurement data in fusion plasma science. However, it is not possible to perfectly model all the noise sources and their distributions. In this work, we propose a more data-driven approach for the noise modeling of multichannel measurement systems. We directly modeled the noise distribution by tractable density distributions parameterized with neural networks and trained their weights from a vast amount of measurement data. We demonstrated an application of this method in Thomson scattering measurement data for the Large Helical Device project. This method enabled us to make a realistic inference even without sufficient prior knowledge about the noise.

Collisional--radiative (CR) models based on \textit{ab initio} atomic structure calculation have been utilized over 20 years to analyze many-electron atomic and ionic spectra. Although the population distribution of the excited states in plasmas and their emission spectra are computed using the CR models, systematic and analytical understanding of the population kinetics are still lacking. % In this work, we present a reduced model of the population dynamics in many-electron atomic ions, in which we approximate the dense energy structure of complex many-electron atoms by a continuum, a continuous CR model (CCRM). Using this simplification, we show an analytical population distribution of many-electron atoms in plasmas and its electron-density and temperature dependence. % In particular, the CCRM shows that the population distribution of highly excited states of many-electron atoms in plasmas resembles a Boltzmann distribution but with an effective excitation temperature. We also show the existence of three typical electron-density regions and two electron-temperature regions where the parameter dependence of the excitation temperature is different. Analytical representations of the effective excitation temperature and the boundaries of these phases are also presented.

Production of a plasma that has a large degree of ionization (DOI), volume, and spatial and temporal uniformities is a challenge for the improvement of the performance of plasma-based vapor deposition processes. As a potential candidate for the discharge, we investigate plasma parameters arising in helium electron cyclotron resonance (ECR) discharges due to a simple cusp field. Two-dimensional distributions of helium atom emission-line intensities were measured using spectroscopy with multiple viewing chords and then de-convoluted by Abel inversion. The local plasma parameters, including the atomic density, were evaluated using collisional-radiative model analysis. The DOI calculated from the electron and atomic densities reached up to 35% and, in most of the region inside the ECR surface, it was more than 10%.

The Balmer-α line profile observed from high-temperature magnetized plasmas can be interpreted as the sum of narrow and broad components corresponding to the emission from atoms generated in edge a...

The effect of 0–7 T magnetic field on the low wavelength resolution photoluminescence (PL) spectrum used for the all-optical thermometry was investigated. The PL spectra averaged over randomly-oriented color centers at the temperature between 283 and 343 K were measured for the analysis. Approximately 0.1% increase in the PL intensity was found at the longer wavelength side of the zero-phonon line (ZPL) with increasing the field strength. Its effect on the evaluated temperatures using the ZPL relative peak intensity and peak wavelength was less than their uncertainties of 8.7 and 3.7 K at 293 K, respectively.

We developed a method to infer the calibration parameters of multichannel measurement systems, such as channel variations of sensitivity and noise amplitude, from experimental data. We regard such uncertainties of the calibration parameters as dependent noise. The statistical properties of the dependent noise and that of the latent functions were modeled and implemented in the Gaussian process kernel. Based on their statistical difference, both parameters were inferred from the data. We applied this method to the electron density measurement system by Thomson scattering for Large Helical Device plasma, which is equipped with 141 spatial channels. Based on the 210 sets of experimental data, we evaluated the correction factor of the sensitivity and noise amplitude for each channel. The correction factor varies by $\approx$ 10\%, and the random noise amplitude is $\approx$ 2\%, i.e., the measurement accuracy increases by a factor of 5 after this sensitivity correction. The certainty improvement in the spatial derivative inference was demonstrated.

In spectroscopic measurements of magnetically confined torus plasmas, the line-integrated emission along a viewing chord is usually observed. However, by utilizing the dependence of the magnitude of the Zeeman splitting on the emission location, a few localized emissions existing along the viewing chord can be separated. A detailed analysis of the Zeeman split spectral lineshapes then makes it possible to evaluate the local values of the magnetic field strength, population density, temperature, and flow velocity. We have introduced polarization spectroscopy to improve the accuracy in separating the overlapped spectra. The polarization resolved Hα, He I, and H2 Fulcher-α band spectra are measured in the TRIAM-1M tokamak, and the atomic and molecular dynamics are investigated. Further progress in the simultaneous measurements of the Balmer series and Fulcher-α band spectra in LHD, and extension to the CH Gerö band spectra, are briefly presented.

A passive spectroscopic method that can measure spatially resolved emission spectra only by observing from a single diagnostic port without assuming plasma symmetry was applied to the stellarator-heliotron device Heliotron J. The emission spectra from the inboard and outboard sides were separated using the difference in their Zeeman effects. On the basis of the fact that in a spectrum as a function of the wavelength, the magnitude of the wavelength splitting by the Zeeman effect relative to the Doppler broadening increases with the wavelength, the method was applied to a near-infrared helium emission line (He I 1s2s 3S−1s2p 3P, 1083 nm), and it was confirmed that the uncertainty in the separated spectra was reduced compared with that in the application to visible emission lines. From the emissivity of the separated spectra, the local recycling flux was evaluated using the inverse photon efficiency method.

The anisotropy in the electron velocity distribution (EVD) was measured using the polarization of two helium atom emission lines, 21P–31D (668 nm) and 23P–33D (588 nm), in a helium electron cyclotron resonance (ECR) discharge plasma. A small polarization degree of less than 4% was measured by adopting a temporal modulation technique. It was found that the polarization originated locally from around the ECR layer and that the anisotropic component of the EVD produced by ECR heating had an average kinetic energy of approximately 40 eV.

The intensity ratios between specific pairs of helium atom (HeI) emission lines are functions of the electron temperature (Te) and density (ne), and these functions have been used for the analysis of Te and ne in various types of discharge plasma. We applied this method to a low-density (ne

The lubrication mechanism of articular cartilage is characterized by an efficient performance. In this work, friction of articular cartilage was evaluated with in-site images of articular surface. The images were captured with the laser light reflected at the interface between a prism and articular cartilage. The attenuation of reflectance was associated with the increase of the contact of collagen network of articular cartilage. The light reflectance and friction coefficient for short sliding presented a significant positive correlation. Friction tests were also carried out for short (30 s) and long (300 s) preloading times. The results indicate that depletion of fluid film is responsible for the increase of friction and the recovery of the fluid film was observed for the long preloading after the early stage of sliding.

We have irradiated CuCl films, which are prepared by a vacuum vapor deposition method, with pico-second light pulses of 82 MHz repetition rate at the photon energy of 3.290 eV. After a long time of photo-irradiation, the photo-irradiated region is recognized by eye for thin films. We observe the surface morphology by atomic force microscopy at room temperature. For a 50 nm thick film, surface structure changes such as surface smoothing, nanometer-scale and micrometer-scale structures formation are observed, which depend on the position in the photo-irradiated region, while such changes are not detected for a 200 nm thick film. The effects of ablation and local heating by the photo-irradiation are excluded for the mechanism of the observed morphology change. The abundance change of Cu and Cl in the film is also detected by the Auger microprobe measurement. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Laight propagation through a gold film with a periodically structured 50 nm width slit array into Cu2O has been calculated with a FDTD (Finite Difference Time Domain) method with a 5 nm mesh-grid. Owing to the presence of a guided mode in the slit and a surface plasmon mode at the gold/Cu2O interface, optical near field generation in Cu2O are efficient in the case where the polarization of the incident light is perpendicular to the slit. The efficiency of the electric quadrupole (E2) transition of the 1s -exciton in Cu2O, which is modified by the field gradient of the excitation light, is evaluated for the calculated optical near field. Slit period dependences of the near field generation and the E2 transition efficiency are examined for a 50 nm thick array film. The enhancement of the effective E2 transition efficiency in the volume of 50 nm thickness above the film relative to the efficiency by the plane wave excitation is found to reach a factor 28 at the slit period of 110 nm. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In a positive column of a glow discharge in the magnetic field of 36.4 G, a linearly polarized laser pulse or a circularly polarized laser pulse has produced polarized neon atoms (alignment or orientation) in the 2 p 2 (Paschen notation) level from the 1 s 3 level. The subsequent fluorescence to the 1 s 2 level was observed with its polarized components resolved. Depopulation, disorientation and disalignment rates of the 2 p 2 atom were measured and their discharge current dependences were examined for a discharge current from 0.4 to 2.0 mA. The degrees of radiation re-absorption, or the optical thickness, of the transition lines from the 2 p 2 level to the 1 s 2 - 1 s 5 levels were measured as functions of the discharge current. A Monte Carlo simulation was performed by which the depopulation, disorientation and disalignment rates by the radiation re-absorption for these transitions were determined. The calculated rates were compared with the observed ones and found to reproduce the their discharge current dependences. D’Yankonov and Perel's analytical expression for these rates was quantified from comparison with the Monte Carlo results.

We have vapor-deposited CuCl films on rutile TiO 2 , Al 2 O 3 and synthesized quartz surfaces. The photoluminescence spectra of the films with the thickness from 50 to 1500 nm were observed and com...

We have irradiated vapor-deposited CuCl films and bulk CuCl at 4.6 K with picosecond light pulses of 82 MHz repetition rate at the photon energy of 3.29 eV. Exciton luminescence having longitudinal optical (LO) phonon structures appeared in the time scale of an hour. Temperature dependences of the intensities of this luminescence and the I 1 luminescence suggested that both the luminescence bands quenched by thermal activation from the relevant bound exciton states to the Z 3 exciton state.

We have observed luminescence spectra of vapor-deposited CuCl films on rutile TiO 2 under photo-irradiation with picosecond light pulses at 4.6 K. Decrease in the Z 3 -exciton and I 1 luminescence intensities and an appearance of new exciton luminescence are found to be induced by the photo-irradiation. From the excitation photon energy dependence of the luminescence spectra, it is found that the Z 3 -exciton luminescence is resolved into two components: one is attributed to the optical phonon Raman lines and the other to the free Z 3 -exciton luminescence. The intensity of the Raman lines resonantly increases at the Z 3 -exciton band resulting in the optical phonon structures in the excitation spectrum. The excitation spectra of the new exciton and I 1 luminescence are similar to the absorption spectrum of CuCl, which suggest that the resonant Raman process observed in the Z 3 -exciton luminescence hardly contributes to the generation of the excitons associated with the new exciton and I 1 luminescence.

Disorientation and disalignment of neon excited atoms in the fine-structure 2p2 level (in Paschen notation) of the 2p53p configuration have been investigated in a helium–neon glow discharge at temperatures between 17 and 300 K. The determined rate coefficients for disorientation, Rdo, and disalignment, Rda, due to helium atom collisions show similar temperature dependences of T1.6 below 77 K with the ratio about Rdo:Rda = 2:1. This fact indicates that both the excitation transfer cross sections between the mJ = 1 and mJ = −1 states, σ1–1, and between the mJ = ±1 and mJ = 0 states, σ10, due to helium atom collisions have similar energy dependences of E1.1 with the ratio about σ1–1:σ10 = 2.5:1 below 10 meV.

Velocity distributions of the 1s 3 (Paschen notation) metastable argon atoms (Ar * ) in a 1 mm thick glow discharge cell have been examined by a Monte Carlo simulation model including Ar * (1s 3 )–Ar elastic collisions and collisional quenching of Ar * atoms at the cell surface. In order to describe the elastic collisions, the differential cross sections, the collision kernels and the collision rate coefficients were calculated from Ar * (1s 3 )–Ar potentials. The calculated velocity distributions with the model were in good agreement with the absorption spectra of the Ar * (1s 3 ) atoms measured by single beam absorption spectroscopy with the thin cell.

Saturated absorption spectra of the 1s 3 –2p 2 (Paschen notation) line of metastable argon (Ar * ) atoms in a 1 mm thick glow discharge cell have been observed at room temperature. We examined the pressure dependence of the spectra from 0.025 to 0.5 torr. The profiles of the spectra were compared with the velocity-changing collision kernels of the Ar * (1s 3 )–Ar collisions. The results suggest that the saturated absorption spectroscopy with the thin cell is useful to detect collision kernels of metastable atoms.

Absorption spectrum of the evanescent light at a glass/Rb vapor interface has been observed with atom density from 9 ×10 19 m -3 to 5 ×10 20 m -3 . Absorption is as high as 60% at the peak of a hyp...

A scheme for the detection of cold metastable atoms at surfaces with spatial and temporal resolution is studied experimentally, using methods of laser cooling and atom optics. Electron emission yields for deexcitation of the metastable states 1s5(J=2) and 1s3(J=0) of argon at a gold surface are compared with a technique that is based on optical pumping and the use of an evanescent-wave atom mirror as an internal-state filter, and are found to agree to within an uncertainty of 10%. The application of the detection scheme to time-of-flight spectroscopy of cold atom clouds is demonstrated. The detector has a field of view of 3 mm diameter, a spatial resolution of order 100 μm, and a time resolution of 20 μs, and the single-atom detection efficiency near the center of the field of view is 14% in the linear counting regime of up to 106 atoms/s.

Disalignment of neon excited atoms in the fine-structure 2p i levels (in Paschen notation) of the 2p 5 3p configuration is investigated in a helium–neon glow discharge at temperatures between 15 and 77 K. At several temperatures, we plot the disalignment rate as a function of the helium atom density for Ne ∗ (2p2 or 2p7 )+H e(1s 2 ) collisions. The slope of this dependence gives the disalignment rate coefficient. For both collisions, the experimental data for the disalignment rate coefficient show a more rapid decrease with the decrease in temperature below 40 K than our quantum close-coupling calculations based on the model potential of Hennecart and Masnou-Seeuws (1985J. Phys. B: At. Mol.Phys. 18 657). This finding suggests that the disalignment cross section rapidly decreases below a few millielectronvolts, in disagreement with our theoretical quantum calculations which predict a strong increase below 1 meV. The disagreement suggests that the long-range electrostatic potentials are significantly more repulsive than in the aforementioned model.

We have observed emission spectra of a CuCl film on a TiO2 prism surface(110) associated with the two-photon excitation of the exciton system in total reflection geometry. The I1 bound exciton emission, which resonantly appeared at the two-photon excitation of the Z3-longitudinal excitons and Z1,2-exciton band, was observed. The dependence of the emission intensities on the polarization of the excitation light was explained from the field intensity and the penetration depth of the evanescent light in CuCl accompanying the totally reflected light at the TiO2/CuCl interface.

For an argon glow discharge in a 1 mm thick cell at room temperature, we have observed the absorption spectrum of the 1s3–2p2 (Paschen notation) line by using a diode laser. It is found that, with a decrease in the gas pressure below 0.1 Torr, the linewidth drastically decreases; at 0.02 Torr the velocity distribution of the metastable atoms in the surface normal direction has an apparent temperature of 144 K. The velocity distribution is also found to be anisotropic: the spectrum profile depends on the direction of observation with respect to the surface normal. These phenomena are explained by a model in which the velocity distribution of the metastable atoms is controlled by collisional quenching at the wall surface and velocity-changing collisions with ground state atoms.

We generated a 0.3-mm-diameter DC, hollow-cathode helium discharge in a gas pressure range of 10–80 kPa. In discharge plasmas, we measured position-dependent laser absorption spectra for helium 23S1–23P0 transition with a spatial resolution of 55 µm. From the results of the analysis of the measured spectra using Voigt functions and including both the Doppler and collision broadening, we produced two-dimensional maps of the metastable 23S1 atomic densities and gas temperatures of the plasmas. We found that, at all pressures, the gas temperatures were approximately uniform in space with values in the range of 400–1500 K and the 23S1 atomic densities were ~1019 m−3. We also found that the two-dimensional density distribution profiles became ring-shaped at high gas pressures, which is qualitatively consistent with the two-dimensional fluid simulation results.

For an electron cyclotron resonance (ECR) discharge, a simple cusp field can improve electron confinement and enhance the degree of ionization (DOI) without sacrificing accessibility to the plasma. In this study, the spatial distribution of the DOI is experimentally revealed in a helium plasma produced with widely used 2.45 GHz and 800 W microwaves. The DOI is evaluated from the electron density and ground state atom density measured using HeI emission line intensities and by collisional-radiative model analysis. It is found that the DOI increases to more than 15% within a reasonably large volume surrounded by the ECR surface and locally reaches as high as 25%.

The magnitude and direction of linear polarization in the HeI 21P–31D emission line are simultaneously measured using a beam-splitting-type polarization spectroscopy system. The polarization measured in the steady-state phase of an electron cyclotron resonance (ECR) discharge produced in a simple cusp field is directed closely perpendicular to the magnetic field at the ECR surface, and the degree of polarization increases up to 8% when the neutral pressure is reduced to less than 23 mPa. These results suggest that the cause of the polarization is attributable to impact excitation by high-energy electrons produced at the ECR surface.

We report development of a high dynamic range spectroscopic system comprising a spectrometer with 30% throughput and a camera with a low-noise fast-readout complementary metal-oxide semiconductor sensor. The system achieves a 10(6) dynamic range (∼20 bit resolution) and an instrumental function approximated by a Voigt profile with Gauss and Lorentz widths of 31 and 0.31 pm, respectively, for 656 nm light. The application of the system for line profile observations of the Balmer-α emissions from high temperature plasmas generated in the Large Helical Device is also presented. In the observed line profiles, emissions are detected in far wings more than 1.0 nm away from the line center, equivalent to neutral hydrogen atom kinetic energies above 1 keV. We evaluate atom density distributions in the core plasma by analyzing the line profiles.

We have simultaneously measured high resolution emission spectra of the hydrogen atomic Balmer-α, -β, -γ lines and molecular Fulcher-α band for a LHD peripheral plasma generated under a central magnetic field strength of 0.4 T. It is found that the velocity distributions of excited atoms calculated from the Balmer-α, -β, and -γ line shapes show similar profiles to each other. The translational kinetic energy corresponding to the average velocity is about 13 eV, which is about 300 times larger than the rotational energy of hydrogen molecules estimated from the line intensities in the Fulcher-α band. The velocity distributions differ from Maxwellian and have a high velocity tail over 1×10 5 m/s. A correlation between the high velocity tail and the electron temperature and density is seen and suggesting the excited atoms having such high velocities to be generated by the charge exchange collisions from high velocity protons in the peripheral region.