Yuuji Okamoto

Absolute calibration of space- and time-resolving flat-field vacuum ultraviolet spectrograph under both P and S polarized light conditions for plasma diagnostics

Measurement of spectra in the wavelength range from vacuum ultraviolet (VUV) to soft x ray is an important means to diagnose impurity behavior in magnetically confined plasmas used in fusion plasmas. Recently, a space- and time-resolving flat-field grazing-incidence VUV spectrograph was constructed for the simultaneous observation of spatial, temporal, and spectral distributions of plasma radiation in the wavelength range of 150–1050 A. Absolute calibration experiments were performed at beamline 11C and beamline 12A in the Photon Factory at the High Energy Acceleration Research Organization. The absolute sensitivity of the VUV spectrograph was measured under both P and S polarized light conditions.

Calibration of space-resolving VUV and soft X-ray spectrographs for plasma diagnostics

Vacuum ultraviolet (VUV) and soft X-ray measurements are important means of diagnosing impurities in magnetically confined plasmas used in fusion research. Recently, space- and time-resolving flat-field VUV (150-1050 A) and soft X-ray (20-350 A) spectrographs have been constructed by using aberration-corrected concave gratings with varied-spacing grooves which give a wide simultaneous spectral coverage on a microchannel-plate intensified detector. Calibration experiments have been performed at beamlines 11A and 11C at the Photon Factory of the High Energy Accelerator Research Organization. The relative efficiency of the VUV spectrograph has been measured for P-polarization geometry in the spectrograph. In the soft X-ray spectrograph, efficiencies have been obtained for several different points of irradiation on the grating along the groove direction and for two (S and P) polarization geometries.

Space-resolving VUV and soft X-ray spectroscopy in the tandem mirror gamma 10 plasma

Vacuum ultraviolet (VUV) and soft X-ray (SX) spectroscopic measurements are important means to diagnose radiation power loss, impurity ion densities and effective charge of confined plasma, Zeff, in magnetically confined plasmas such as fusion plasmas. We have constructed space- and time-resolving flat-field VUV (150–1050A) and SX (20–350A) spectrographs by using aberration-corrected concave gratings with varied line spacing. Absolute calibration experiments have been conducted at the Photon Factory in the High Energy Accelerator Research Organization. Absolute sensitivities of the VUV and SX spectrographs have been obtained for the two (S and P) polarization geometries. Thus, absolute intensities of emission spectra from impurity ions can be measured together with their radial distributions in plasmas. The total radiation power was determined to be less than 6 kW within ±20% of error in our normal plasma operation. Density profiles of impurity ions were reduced by using absolute emissivities of impurity lines and a collisional-radiative model. Moreover, the value of Zeff is estimated to be 1.00 in the tandem mirror GAMMA 10 plasma.

Absolute Calibration of Space- and Time-Resolving Flat-Field Vacuum Ultraviolet Spectrograph for Plasma Diagnostics

Measurement of spectra in the wavelength range from vacuum ultraviolet (VUV) to soft X-ray is an important means to diagnose impurities in magnetically confined plasmas used in fusion plasmas such as a GAMMA10 plasma. Recently, a space- and time-resolving flat-field grazing-incidence VUV spectrograph was constructed for the simultaneous observation of spatial, temporal and spectral distributions of plasma radiation in the wavelength range of 150–1050 A. Absolute calibration experiments were performed at beamline 11C in the Photon Factory at the High Energy Accelerator Research Organization. The absolute efficiency of the VUV spectrograph was measured for P polarization geometry in the spectrograph.

Spectroscopic measurement of impurity ion behavior in the GAMMA10 tandem mirror

Behavior of impurity ions has been investigated using visible spectroscopy in the GAMMA10 tandem mirror. A 40 channel visible spectrometer system has been developed for measurements of the ion temperature and ion flow velocity. The spectrometer consists of a 100 cm monochromator, a 40 channel optical fiber array and an image intensifier tube coupled with a charge coupled device TV camera. The spectra from low ionization states of oxygen and carbon are measured in ion cyclotron range of frequency heated plasmas. High ion temperatures (3–10 keV) of O4+ are observed in the anchor region, where the minimum B mirror field is produced by baseball coils. The O4+ ion is heated by the fourth harmonic frequency of O4+, which is most likely due to the cyclotron higher harmonic damping.

Two-dimensional imaging X-ray spectrometer for plasma diagnostics

Abstract A two-dimensional imaging soft X-ray monochromator is now under development. The main components of this spectrometer are a channel plate collimator (CPC) and multilayer mirrors. We have applied this monochromator to obtain soft X-ray images of GAMMAIO tandem mirror plasmas. In order to obtain clear images in a low energy X-ray regime, we have utilized and tested a focusing effect of the CPC. Ray-trace simulations were carried out under the same conditions as the experiments. After comparison of these results, we have confirmed that the focusing effect of the CPC is useful in practical use. Monochromatized two-dimensional soft X-ray images have been successfully taken on the tandem mirror experiment.

Current Response Characteristics of Microchannel Plates for Detection Vacuum‐Ultraviolet Radiation

The current response characteristics of microchannel plates (MCPs) for detection of x‐rays have been investigated using synchrotron radiation in the vacuum‐ultraviolet (VUV) band (the wavelength range 20–80 nm). Calculation from a simple model to account the detection current of MCP are compared with the measured incident angle dependence of MCP response. The result indicates the effect of x‐ray reflection within a channel is important for understanding the detection process on MCPs in the VUV region.

Measurements of Spatial Coherence of Recombination X-Ray Laser

We measured the spatial coherence of a soft X-ray laser pumped through the recombination scheme under various X-ray amplification configurations for the first time. A theoretical calculation model based on two-beam interference with partially coherent, quasimonochromatic light was developed to analyze the observed fringe patterns. The X-ray source is assumed to have a Gaussian intensity distribution. We also introduced a deviation at the peak position of the X-ray source from the optical axis in the experiments on Youngs interference. In the experiments, the fringe pattern representing the interference from the pair of Youngs slits was observed for the Al XI 3d–4f line (15.47 nm), while the fringe visibility for the other nonlasing lines was not observed. It is clarified that the spatial coherence of the Al XI 3d–4f line developes in accordance with its amplification.

Spatial Coherence of Recombination X‐ray Laser Pumped by Pulse‐Train Laser

We have started measurements of spatial coherence of x‐ray radiation from recombination x‐ray laser source that is pumped by pulse‐train laser. The dispersing coherence diagnostic system has been constructed. In the preliminary experiments using double‐slits of 24 μm and 50 μm separations, fringe patterns representing the interference from the pair of Young’s slits have been observed for the Al XI 3d‐4f line. The measured fringe visibility was 0.3 for 50 μm separated two points at 370 mm distant from the source. On the other hand, there have not been observed any clear fringe visibility for the other non‐lasing lines.

Calibration of Time- and Space-Resolving Vacuum Ultraviolet Spectrograph for Plasma Diagnostics in the Tandem Mirror GAMMA 10.

A time- and space-resolving vacuum ultraviolet (VUV) spectrograph has been developed and is applied as an impurity diagnostic in the tandem mirror GAMMA 10. The VUV spectrograph enables us to analyze the spatial distributions of plasma radiation in the wavelength range from 15 nm to 105 nm. Calibration of the VUV spectrograph was carried out in order to determine the sensitivity of the spectrograph as a function of wavelength. We also established a method of analyzing the emissivity profiles of each spectral source in a visual manner from spatially resolved VUV spectrophotograph in the GAMMA 10.