Local Emission Coefficients Research Articles

전리수소 영역의 물리량 측정을 위한 방출선 모형연구

A diagnostic tool has been proposed to convert the observed surface distribution of hydrogen recombination line intensities into the radial distributions of the electron temperature and the density in HII regions. The observed line intensity is given by an integral of the volume emission coefficient along the line of sight, which comprises the Abel type integral equation for the volume emission coefficient. As the emission coefficient at a position is determined by the temperature and density of electrons at the position, the local emission coefficient resulted from the solution of the Abel equation gives the radial distribution of the temperature and the density. A test has been done on the feasibility of our diagnostic approach to probing of HII regions. From model calculations of an HII region of pure hydrogen, we have theoretically generated the observed surface brightness of hydrogen recombination line intensities and analyzed them by our diagnostic tool. The resulting temperatures and densities are then compared with the model values. For this case of uniform density, errors in the derived density are not large at all the positions. For the electron temperature, however, the largest errors appear at the central part of the HII region. The errors in the derived temperature decrease with the radial distance, and become negligible in the outer part of the model HII region.

Tomographic diagnostics of high-frequency electrodeless lamps in argon–mercury mixtures

Tomographic reconstruction of spatial profiles of the mercury atom density in the excited state 7 3S1 in high-frequency electrodeless lamps (HFELs) has been performed. The measurements of the Hg 546.1 nm line emission intensity have been made for the HFELs in argon–mercury mixture depending on the operation regime with different cold spot temperatures in the range 31–98 °C. The maximum entropy-based algorithm was applied for the reconstruction of local emission coefficients from the integrated intensities. The emission coefficients are directly related to the local values of the mercury atom density in the excited state 7 3S1, the upper state of the 546.1 nm transition. Such an investigation has been performed first for the HFEL. We have found that the emitting mercury atoms in the state 7 3S1 are concentrated in a thin layer located close to the lamp wall. The radial profiles have demonstrated a strong depletion of the population density in the state 7 3S1 from the lamp centre at high generator currents and low mercury vapour density. The obtained results are analysed theoretically in the context of the radial cataphoresis phenomenon. We found a qualitative agreement between the reconstructed density profiles and theoretical model predictions.

Space-time Resolved Spectroscopic System Based on a Rotating Hexahedral Mirror for Measurement of Visible and Ultraviolet Spectral Line Emissions

By using a rotating hexahedral mirror placed in front of the objective lens and two sets of visible and ultraviolet monochromators coupled with a branchy quartz fiber bundle, a spacetime resolved spectroscopic system has been developed on the HT-7 superconducting tokamak. A center monitoring system has been used including a Helium-Neon laser and a photodiode detector to indicate the absolute position of the measurement in order to reduce the error caused by the uncertain emissive position of the plasma. By using the asymmetric Abel inversion, the spacetime resolved local emission coefficients of the spectroscopic line emissions have been obtained. Presented in this article are simultaneous measurements of two spectral line emissions such as CV-227.1 nm and OV-278.1 nm during a single plasma discharge on the HT-7. Experimental results indicate that the time resolution is better than 3 ms, the space resolution is better than 1.5 cm, the ratio of signal to background is better than 10:1, and the relative error of chord-integrated emission profile is less than 10%. Compared to traditional multichannel detecting systems, this system has considerably improved measurement efficiency, reduced uncertainty, and is therefore suitable for transport studies of global particles and impurities.

Three-dimensional emission tomography of a scattering plasma

The three-dimensional emission ray tomography of a plasma partially scattering its self-radiation is considered. The spatial distribution of scattering density and its angular distribution are assumed to be known. The model of projection-data acquisition taking into account single and multiple scattering is constructed. In terms of this model, the problem of determining the distribution of local emission coefficients is posed. For solving this problem, the algorithm based on the Neumann-series expansion of the product of the radiative-transfer operator for a scattering medium and the operator for solving the pure emission problem was proposed. The algorithm was investigated in detail using numerical simulation.

Novel instrumentation for spectrally resolved soft x-ray plasma tomography: Development and pilot results on TEXTOR

A novel instrumentation for wavelength- and time-resolved plasma emission tomography in the range 0.1–4 keV has been demonstrated on the Torus Experiment for Technology Oriented Research (TEXTOR). The technique is intended for reconstruction of distributions of local emission coefficients (LEC) for selected spectral lines of impurity ions. Further determination (with additional data on electron density and temperature) of spatial distributions of impurity ions at particular ionization stages will become feasible. Spectrally selective plasma images at several viewpoints around plasma are obtained with miniature pinhole cameras supplemented with multilayer mirrors as dispersion elements. The x-ray image is converted to a visible image and transported by a fiber bundle to a gain enhanced recording camera with an electron bombarded charge coupled device tube. A part of the system has been installed on temporary TEXTOR ports. First demonstration results have been obtained on plasma imaging and on subsequent LEC reconstruction using a modified iterative sinogram restoration tomography algorithm. The complete diagnostics will be operational after the TEXTOR shutdown in 2001.

Three-dimensional emission tomography of optically thick plasma for the known absorption

The three-dimensional emission tomography of a plasma partially absorbing intrinsic emission is studied. The distribution of local absorption coefficients is assumed to be known. To determine the distribution of local emission coefficients under the given conditions, the use of algebraic algorithms inverting the projection matrix constructed taking into account absorption is proposed. NDAT and NDFBP algorithms are developed, which are based on the expansion of the product of the operator of energy transport in an absorbing medium and the operator of the solution of the problem of emission tomography of a transparent plasma in a Neumann series. A numerical simulation is made, which shows that the emission field can be reconstructed with a reasonable accuracy for an optical thickness as high as 6–8.

Measurements of relative transition probabilities of ns-4p, nd-4p, and nf-3d transitions in neutral potassium

Relative transition probability ( A-value) measurements are reported for the ns-4 p ( n = 6–15), nd-4 p ( n = 5–13), and nf-3 d ( n = 7–14) series transitions in neutral potassium (KI). The results are based on intensity measurements of optically-thin KI spectral lines from a steady-state potassium emission source. The source employed was a radially-symmetric potassium-seeded argon plasmajet containing ≲ 5 mole per cent K-atoms. Local emission coefficients were obtained by means of the Abel transform. For the prevailing free-stream conditions ( P ∼ 11 torr, T ∼ 3200 K, n e ∼ 10 14 cm -3), the potassium excited state populations are described by a Boltzmann distribution down to and including the ground state. The reported A-values are normalized to that of the 580.2 nm line (7 s-4 p 3 2 transition). The relative accuracy is estimated to be 5–20% for the ns-4 p series and 15–25% for the nf-3 d transitions. With the exception of the data for the 6 s-4 p and all nf-3 d transitions, the measurements agree to within estimated experimental uncertainties with the values given in the NBS tabulation [Wiese et al. (1969)], although systematic differences are observed. For the exceptions noted, the measurements lie 25–50% below the relative NBS values. Comparison is also made to recent calculations of Lindgard and Nielson, and Ormonde.

The flow mechanism in a bent, rotating arc

A 5 A arc in a 40% H2, 60% N2 mixture under atmospheric conditions is bent by a magnetic field into approximately a semi-circle and rotates with the frequency of the driving magnetic field, the direction of the deflection being shifted back 50° relative to the Lorentz force. The distribution of the gas temperature is determined from the intensity distribution ofH β, which is measured by a sampling technique and deconvoluted to the local emission coefficient e Hβ without resorting to symmetry properties but with due consideration of LTE deviations. The flow velocity component normal to the isothermal surfaces is evaluated from the convective term of the energy balance equation, whereas the tangential component is calculated from the continuity equation. The flow field is composed of 6 vortices and 6 stagnation points and can be regarded as an interaction of 3 basic processes: 1) a mass flow through the arc in the direction of deflection correlated to the curvature of the arc due to inhomogeneous heating, 2) a closed double vortex in the cross-sectional plane of the arc that is caused by the rotational motion, 3) the decay of unstable shear layers in the flow field, by which two additional pairs of vortices are created.

Measurement of the temperature and flow fields of the magnetically stabilized cross-flow N2 arc

A straight, steady-state cross-flow arc is burning in an N2 wind tunnel. The arc is held in position by the balance of the Lorentz forces produced by an external magnetic field perpendicular to the arc axis and by the viscous forces of the gas flow acting on the arc column. The temperature field in the discharge is determined spectroscopically using the radiation of N I lines. Because of the lack of rotational symmetry an inversion method developed by Maldonado was used to determine the local emission coefficient from the measured integrated spectral intensity distributions across the arc in various directions. For known local temperature the mass flow field inside the arc may be evaluated from the convective term of the energy equation and the continuity equation. This is done by expanding the terms of these two equations around the point of the temperature maximum into Fourier-Taylor series and determining coefficients of the same order and power. The solution of the resulting set of algebraic equations yields the unknown coefficients of the mass flow. The flow field obtained by these calculations shows a relatively strong counterflow through the arc core. In the region for which the series expansion holds a partial structure pertaining to a closed double vortex can be recognized.

Numerical Solution for Local Emission Coefficients in Axisymmetric Self-Absorbed Sources

This paper presents a method for determining local emission and absorption coefficients in an axisymmetric, self-absorbed source which is applicable to laboratory arc plasma jets in current use. In spectrometric diagnosis of arc plasma, physical and chemical properties are established through their theoretical relation to experimental line emission coefficients. These coefficients, however, are not measured directly. The measured line intensity is a result of emitters along the spectroscopic line of sight and is affected by optical thickness, a result of physical depth and absorption in the source. Previous techniques (References 1 through 6), involving a single Abel integral equation, neglect the effect of absorption. There is evidence (References 7 and 8), however, that certain lines are absorbed. In order to minimize the errors in the resulting plasma properties, as discussed in Reference 9, it is desirable to perform an accurate mathematical inversion and account for self-absorption. This requires the solution of two integral equations of the first kind. The method developed here requires spectroscopic observation of the source with and without the presence of a plane mirror (Figure 1). This technique, proposed by Pearce [10], supplies the additional information necessary to experimentally determine the local absorption coefficients. These are used in the solution for emission coefficients. The method is based on an exact solution of the equation of transfer in local radial zones of constant emission and absorption coefficients. The technique has been applied to analytical functions which approximate data to be expected. The accuracy of the numerical methods was determined by comparison with the analytical solutions.