Showing papers by "Hiroyuki A. Sakaue published in 2011"

Intensity Ratio of Density-sensitive Lines in Fe Ions Observed with a Well-defined Laboratory Plasma

Abstract: We present spectra of highly charged Fe ions in the extreme ultraviolet range observed using an electron beam ion trap equipped with a flat-field grazing incidence spectrometer. The density dependence of line intensity ratios is investigated for several density-sensitive lines of Fe XIII, XIV, and XV. Unlike previous studies where the electron density was estimated from theoretical considerations, here it is derived from electron beam profile measurements. The experimental data are compared with model calculations.

High resolution extreme ultraviolet spectrometer for an electron beam ion trap

Abstract: An extreme ultraviolet spectrometer has been developed for spectroscopic studies of highly charged ions with an electron beam ion trap. It has a slit-less configuration with a spherical varied-line-spacing grating that provides a flat focal plane for grazing incidence light. Alternative use of two different gratings enables us to cover the wavelength range 1-25 nm. Test observations with the Tokyo electron beam ion trap demonstrate the high performance of the present spectrometer such as a resolving power of above 1000.

Ab initio multi-configuration Dirac–Fock calculation of M1 visible transitions among the ground state multiplets of the W26 + ion

Abstract: The development of fusion reactors has generated a demand for improved knowledge of the atomic properties of tungsten. Using a multi-configuration Dirac–Fock (MCDF) method with a restricted active space treatment, the wavelengths and transition probabilities of the M1 and E2 transitions in the visible light region are calculated for the ground state multiplets of W26 + ions. The theoretical wavelength (388.43 nm) for the 3H5 → 3H4 magnetic dipole transition agrees quite well with the experimental value (389.41 nm). Other transitions theoretically predicted at longer wavelengths are also in good agreement with new experimental observations. The results also indicate that the core–core correlation contributions from the 4d shell are essential to determine the transition properties accurately.

Interpretation of spectral emission in the 20 nm region from tungsten ions observed in fusion device plasmas

Abstract: We have measured extreme ultraviolet spectra from tungsten ions in the 20 nm region in plasmas produced in the Large Helical Device at the National Institute for Fusion Science. The spectra following injection of a tungsten pellet into a hydrogen plasma were monitored by a grazing incidence spectrometer. A quasicontinuum spectral feature arising from an unresolved transition array (UTA) was observed around 20 nm in plasmas with temperatures below 1.0 keV. This structure is reasonably considered to be the same as observed in another tokamak device or laser-produced plasmas under low-temperature conditions. Atomic structure calculations have been performed for tungsten ions with open 5p, 5s and 4f subshells (W7 +–W27 +) to interpret the observed feature around 20 nm. Wavelengths and strengths for these transitions were calculated, and mean wavelengths and extent of the UTAs were compared with the observations, which suggests that the emission largely arises from n = 5–5 transitions in stages lower than W27 +.

Simple Method of Synthesizing Nickel?Nitrilotriacetic Acid Gold Nanoparticles with a Narrow Size Distribution for Protein Labeling

Abstract: We developed a simple method to synthesize nickel–nitrilotriacetic acid gold nanoparticles (Ni–NTA Au NPs) with a narrow size distribution for site-specific labeling in protein complexes. Au NPs were synthesized by the reduction of HAuCl4 using trisodium citrate and tannin acid. Then, the nanoparticle surfaces were modified with NTA and subsequent complexation with Ni2+. The mean diameter of the synthesized Ni–NTA Au NPs was 4.3 nm, and the coefficient of variation was 9%. The specific binding of the Ni–NTA Au NPs to polyhistidine-tagged (His-tagged) proteins was determined by transmission electron microscopy using kinesin and the p62 subunit of dynactin. Consequently, our method is useful for analyzing the substructures of protein complexes.

Visible spectroscopy of highly charged tungsten ions

Abstract: We present visible spectra of highly charged tungsten ions observed by using a compact electron beam ion trap. The newly observed lines and the ions responsible for them, identified by the electron energy dependence of the lines, are presented. Theoretical calculations performed for the detailed identification of the lines are also presented. Finally, the experimental and the theoretical results are compared.

Electron density dependence of intensity ratio for FeXXII extreme ultraviolet emission lines arising from different ground levels in electron beam ion trap and large helical device

Abstract: Extreme ultraviolet (EUV) spectra of highly charged iron ions in a wavelength range of 100–300 A have been observed from two different plasma sources of the Tokyo Electron Beam Ion Trap (Tokyo-EBIT) with a monoenergetic electron beam and a Large Helical Device (LHD) with Maxwellian electron energy. The excitation process of the spectral lines is compared between the two plasmas, and it is found that the excitation process for Fe XIX - Fe XXII ions is clearly different. Namely, the EUV emission lines from the EBIT plasma are only dominated by electron impact excitation connected to the ground state, but the excitation mechanism is not so simple in the LHD plasma. The difference in the excitation process is studied by measuring the intensity ratio of EUV emission lines (114.412 A [1s22s2p2 2P3/2 → 1s22s22p 2P3/2]/117.144 A [1s22s2p2 2P1/2 → 1s22s22p 2P1/2]) arising from different ground levels in the Fe XXII ions. The line intensity ratio has an extremely small value of 0.2 in the EBIT plasma with a low bea...

EUV spectroscopy of highly charged ions with high- and low-energy EBITs

Abstract: Spectra of highly charged ions in the extreme ultraviolet range were observed using high- and low-energy electron beam ion traps (EBITs) in Tokyo. For efficient observation, a slitless grazing incidence flat field spectrometer was specially designed for each EBIT. The present results demonstrate that the complementary use of these spectrometers enable spectroscopic studies of ions with a wide range of charge states.

Charge-Transfer Cross Sections of H+ Ions in Collisions with Noble Gas Atoms in the Energy Range below 4.0 keV

Abstract: Charge-transfer cross sections in collisions of H+ ions with the ground state He, Ar, Kr, and Xe atoms have been measured in the energy range below 4.0 keV with the initial growth rate method. These observed cross sections are also compared with previously published experimental data and theoretical predictions. In the He and Ar targets, it is found that some previous experimental data deviate significantly from the present observed cross sections as the collision energy decreases. It has been found that in the Kr and Xe targets, the energy dependence of the present observed cross sections behaves as “near-resonant” charge transfer.

Database and Related Activities in Japan

Abstract: We have constructed and made available atomic and molecular (AM) numerical databases on collision processes such as electron‐impact excitation and ionization, recombination and charge transfer of atoms and molecules relevant for plasma physics, fusion research, astrophysics, applied‐science plasma, and other related areas. The retrievable data is freely accessible via the internet. We also work on atomic data evaluation and constructing collisional‐radiative models for spectroscopic plasma diagnostics. Recently we have worked on Fe ions and W ions theoretically and experimentally. The atomic data and collisional‐radiative models for these ions are examined and applied to laboratory plasmas. A visible M1 transition of W26+ ion is identified at 389.41 nm by EBIT experiments and theoretical calculations. We have small non‐retrievable databases in addition to our main database. Recently we evaluated photo‐absorption cross sections for 9 atoms and 23 molecules and we present them as a new database. We establis...

Measurement of EUV spectra from high Z elements in the Large Helical Device

Abstract: Extreme ultra‐violet (EUV) emission spectra from highly charged tin, xenon and tungsten ions have been measured in optically thin high‐temperature plasmas produced in the Large Helical Device (LHD) at the National Institute for Fusion Science by using a grazing incidence spectrometer and a tracer‐encapsulated solid pellet (TESPEL) injector. Quasi‐continuous spectral features arising from unresolved transition array (UTA) of open 4d subshell ions were observed for tin, xenon and tungsten around 13.5, 11, and 5 nm, respectively, when edge plasma was cooled sufficiently. The spectral appearance obviously depends on edge electron temperature and atomic number. In the case of intermediate edge temperature, sharp discrete lines from highly charged open 4s or 4p subshell ions are clearly observed for tin and xenon in the longer wavelength side of the UTAs but not the case for tungsten. Assignments of the strong discrete lines have been performed by comparison with other experimental data and the theoretical calculations generated using the Cowan code. In order to interpret the tungsten spectra it was necessary to include the contribution of open 4f subshell ions.

Effect of Radiation Power Loss due to Impurity Gas Puff on Divertor Plasma

Abstract: In order to examine the effect of radiation power loss due to impurity gas puff in divertor plasma, we calculated time evolution of impurity ion densities and electron temperature for several cases with Ne gas puff rates 1012 and 1013 cm−3 s−1 during 0.01 s and initial electron temperature 10-300 eV for a plasma with electron density 1013 cm−3 with a one zone model. We found that the electron temperature decreases less than 1 eV for the cases with gas puff rate 1013 cm−3 s−1, independent of initial electron temperature and in this case we expect plasma detachment. Detailed conditions for plasma detachment should also depend on time history of radiation power.

EUV emission spectra of iron ions following charge exchange collisions with He

Abstract: The emission spectra in collisions of Feq+ (q=8–16) with He were measured in the extreme ultraviolet wavelength region at a collision energy of 20×q keV. The contribution of the double electron capture process cannot be ignored, at least in Feq+ (q=9–13) collisions. By comparing the emission spectra between charge exchange spectroscopy and an electron beam ion trap (EBIT) experiment, the resonance lines can be distinguished from other emission lines in the charge exchange spectra, and the charge state distribution of trapped ions can be estimated from the observed EBIT spectrum.