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%.

An integral analytical formula for a spatial distribution of the optical escape factor ͑OEF͒ in an infinite cylindrical plasma is derived as a function of an arbitrary upper state spatial density profile, the temperature ratio of the upper state to the lower state, and the optical depth of the corresponding transition. Test calculations are carried out for three different upper state profiles, i.e., uniform ͑rectangular͒, parabolic, and Gaussian upper state profiles. The OEF takes on negative values at the periphery of the parabolic and Gaussian upper state profiles. These characteristics cannot be expressed by the conventional OEF formulas derived for the center of the plasma, even though the optical depth is increased. In addition to the analytical derivation of the formula, two practical formulas are proposed: an empirical formula of the spatial distribution of the OEF for the Gaussian upper state density profile and a linear formula of the OEF distribution for upper state profiles that are expressed as linear combinations. These formulas enable us to calculate the spatial distribution of the OEF for the multiple-Gaussian upper state profile without the need for time-consuming integral calculations.

In helium discharge plasmas, the relative emission intensities of the fine-structure transitions belonging to the HeI 2 3 S−2 3 P transition can be affected by radiation reabsorption. Since the magnitude of the reabsorption depends on the density and temperature of the 2 3 S metastable atoms, their density can be determined by measuring the 2 3 S−2 3 P emission line shape using a high wavelength-resolution spectrometer. In this study, the applicable conditions of the method in terms of the opacity and line broadening are revealed, and possible causes of errors in the measurement, i.e., spatial distributions of the density and temperature and the effects of external magnetic and electric fields, are investigated. The effect of reabsorption under an external magnetic field is experimentally confirmed using a glow discharge plasma installed in a superconducting magnet.

In this paper, results of spectral measurement in the end-cell of the GAMMA 10/PDX are described. A spectral measurement system consisting of two spectrometers was developed in order to measure the detailed radiation behavior in D-module. Firstly, angular dependence of the V-shaped target plate on the spatial distribution of the Hα radiance was investigated. It is found that the spectral distribution in Hα intensity along the axial direction is affected by the angle of the target plate. Next, in the experiment with H 2 and Ar gas injection, primary 17 line spectra of Ar I were identified and the radiation loss from Ar neutrals was also evaluated from intensity of spectra. A correlation between the power of radiation loss and the electron temperature in D-module are recognized. The correlation between radiation power and electron temperature is also discussed from the view point of radiation cooling.

The helium 23S metastable atom densities are experimentally evaluated by self-absorption spectroscopy of the HeI 23S–23P transition spectra in two kinds of cylindrical glow discharge plasmas, which have different radii and are operated under different pressures of 300 and 20 Pa. The spectra are measured by using an interference spectroscopy system with a wavelength resolution of about 60 pm, and the relative intensities of the fine structure transitions are analyzed. It is found that the method is in principle applicable to plasmas with the pressure up to about the atmospheric pressure and electron density on the order of up to 1022 m−3. For a plasma with an absorption length of 10 mm and a spatially uniform temperature of 300 K, the method is sensitive to the metastable atom density roughly from 1016 to 1019 m−3.