Mikio Mimura

Intensity calibration of a VUV system by branching line pairs of low ionized light atoms

A method for determining the relative sensitivity of a vacuum ultraviolet (VUV) monochromator is described for the wavelength region from 200 to 1200 A. Eleven VUV line pairs of low ionized atoms of nitrogen and oxygen are selected for which recent data of transition probabilities or branching ratios are available. Calibration is made by measuring the intensity ratios of these line pairs emitted from a stationary helium plasma into which a nitrogen or an oxygen gas is introduced. The results are in good agreement with those obtained using the usual atomic branching ratio method for hydrogen and helium.

Convolution-Fitting Method for Doppler-Broadening Plasma Ion Temperature Measurement

To estimate the ion temperature of plasma using Doppler broadening with a low-resolution monochromator, a convolution-fitting method was proposed. This method utilizes the information of the slit function of the monochromator to improve the effective resolution. It consists of a convolution calculation of trial functions and the slit function, and a fitting of the result with a measured line spectrum. A model experiment was carried out to demonstrate the usefulness of the method. The measured lines were C III 2296.8 A and C V 2270.9 A from JIPP T-IIU Tokamak. The slit function was obtained by measuring Hg I 2656.5 A line from a mercury lamp. Applying the method to these lines, effective resolution was improved by a factor of about seven.

Spectroscopic Measurement of Electron Temperature during Lower Hybrid Current Startup in JIPP T-IIU Tokamak

A simple diagram method is applied to obtain the time evolution of the electron temperature from the time history of the impurity line radiation which appears during the early phases of lower hybrid current startup in the JIPP T-IIU tokamak. This method makes it possible to survey the dependence of the time behavior of impurity emission on various plasma parameters (impurity influx rate, impurity confinement time, etc.). The electron temperature thus obtained agrees well with that derived from the temperature-sensitive line ratio and from Thomson scattering.

A Proposal of a New Technique of Atomic Beam-Doppler Speetroscopy for Electric Field Measurement in Plasma

A new diagnostic technique for the measurement of the electric field in a magnetically confined plasma is proposed. A neutral atomic beam is injected into the plasma as the probe. The local electric field in the plasma can be determined from the optical Doppler shift, which is related to the so-called E×B drift, of a spectral line emitted by those ions which are ionized from the probing beam. The photon number and the spectrum profile is evaluated using a simple model. Two important factors for the present proposal, the necessary intensity of the beam and the resolution of the spectroscopie system are discussed.

Mercury-spectrum measurement with a handmade negative-film diffraction grating

A negative-film diffraction grating was made by taking a photograph of a pattern drawn using an XY-plotter connected to a personal computer. To check the performance of the negative-film grating, a simple monochromator system was built with it. Five spectrum lines in the light from a mercury lamp were observed with the monochromator system.

Development of a high current supersonic ion source for electromagnetic accelerators

Abstract The first report is presented on a supersonic ion source for electromagnetic (EM) accelerators, which in principle affords a much higher ion beam power than electrostatic accelerators because there is no space charge limiting effect. None of the present EM systems, however, operate as expected. The reason for this failure has been analyzed (K. Hirano, J. Plasma Fusion Res., 69 (1993) 684, 806) and attributed mainly to the fact that the EM force does not accelerate but even chokes the subsonic plasma flow which appears during the ionization phase of the inlet gas. Since this difficulty may be overcome by an ion source supplying a supersonic plasma flow to the EM system, development of such an ion source has started based on a thermal arc jet with the aim of yielding an ion current density of about 200 A cm−2. The advantages of a structure with a very narrow arc constrictor hole are known, so a hole size as large as 1 mm in diameter was tested to begin with. Favorable results of the experiments were that the arc jet can produce an arc current of 170 A and ejects a smooth symmetric plasma column from the expanding exit nozzle without producing any notable damage on both the cathode and anode surfaces.

Sensitivity Calibration of a VUV System by Branching Line Pairs of Highly Ionized Atoms

Eight vacuum ultraviolet branching line pairs from C IV, O V, O VI, O VIII and Fe XXI are selected to perform in situ relative sensitivity calibration of a VUV monochromator installed on the JIPP T-IIU tokamak. Details of the behavior of these line pairs in a tokamak plasma are described and discussed. Relative sensitivity calibration in the wavelength region from 75 A through 1230 A is conducted by measuring the intensity ratios of these line pairs and by arranging them by the simple proportional allotment method.

Soft X-ray space- and time-resolving polychromator for plasma diagnostics

Abstract In this paper we describe a polychromator which enables us to observe the time resolution of the spatial distribution of soft X-ray emissions from high temperature plasmas. The polychromator is based on the Rowland circle mount of a spherical grating. An assembly of a two-stage MCP and a fluorescent screen is used as a two-dimensional position-sensitive detector for images of various wavelengths. The images on the fluorescent screen are transferred to a charge-coupled device with a camera lens and read out with a rapid data acquisition system. The spatial distribution of Cu L emissions (about 0.95 keV) from a windowless X-ray tube has been obtained with a spectral resolution of about 5 eV.

Dot character display using a negative-film diffraction grating matrix

A diffraction grating matrix made of negative film is applied to display dot characters. Using an X-Y plotter of a personal computer, a multiple grating pattern is plotted in a matrix form. The photograph of the pattern is the negative-film diffraction grating matrix. When a laser light illuminates the grating matrix, the diffracted light displays a dot character. Several alphabetic characters are displayed in this way.

Efficiencies of diffraction gratings by an electromagnetic theory

Abstract Diffraction efficiencies of several different types of gratings are estimated by using an electromagnetic theory. The result shows that they are in good agreement with observed ones.