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The elemental mixture of Mg-6 wt %Al-1 wt %Zn-0.3 wt %Mn (AZ61B) alloy powder and CaO particles was consolidated by an equal-channel angular bulk mechanical alloying (ECABMA) process to form a composite precursor. Subsequently, the precursor was subjected to a heat treatment to synthesize fine Al2Ca particles via a solid-state reaction between the Mg–Al matrix and CaO additives. Scanning electron microscopy-energy-dispersive spectroscopy (SEM-EDS) and electron probe micro-analysis on the precursor indicated that 4.7-at % Al atoms formed a supersaturated solid solution in the α-Mg matrix. Transmission electron microscopy-EDS and X-ray diffraction analyses on the AZ61B composite precursor with 10-vol % CaO particles obtained by heat treatment confirmed that CaO additives were thermally decomposed in the Mg–Al alloy, and the solid-soluted Ca atoms diffused along the α-Mg grain boundaries. Al atoms also diffused to the grain boundaries because of attraction to the Ca atoms resulting from a strong reactivity between Al and Ca. As a result, needle-like (Mg,Al)2Ca intermetallics were formed as intermediate precipitates in the initial reaction stage during the heat treatment. Finally, the precipitates were transformed into spherical Al2Ca particles by the substitution of Al atoms for Mg atoms in (Mg,Al)2Ca after a long heat treatment.

AZ61B alloy powder composite with Al 2 Ca fine dispersoids was developed by using CaO additive particles as raw materials. For synthesis of Al 2 Ca in the matrix, CaO particles were elementally and uniformly mixed with AZ61B alloy chips via ECABMA process. The mechanism in formation of Al 2 Ca intermetallics was investigated by XRD and SEM–EDS analysis when AZ61B alloy green compacts containing CaO additives were heat treated at 380–625 °C in argon gas atmosphere. A change in a standard free energy in formation of Al 2 Ca via reaction between CaO and Mg–Al alloy was calculated by using a standard Gibbs free energy of each element contained in the green compact. Both of the theoretical analysis by thermo-dynamic and experimental investigation clarified that Al 2 Ca and MgO were synthesized by employing Mg–Al alloy, not pure Mg as the matrix material. Microstructural analysis indicated that needle-like intermetallic of (Mg,Al) 2 Ca or Al 3 Ca 4 Mg were formed as intermediately created compounds in the solid-state reaction between CaO particles and Mg–Al alloy to synthesize Al 2 Ca and MgO dispersoids.

第Ⅲ部 研究所等におけるアーカイブズ活動 第1章, 藤田 順治 [核融合科学研究所・総合研究大学院大学名誉教授]

Around the western part of Teshima Island in Kagawa Prefecture, various types of industrial waste were dumped illegally for about 20 years. The dumped wastes amount to a total of approximately 500,000 tons. The biological monitoring of coastal seawater was carried out using the sea urchin embryo development test to elucidate the influence of polluted seawater on marine organisms. The monitoring was conducted while the seaside restoration was in progress from March 1999 to February 2003. The results of March 2001 showed that the pluteus formation stage decreased from level one to three, and similar results were observed in July, 2001. The decrease coincided with the time after work on seaside restoration had been completed. On the basis of these results, the Apollo-like deformation of sea urchin embryos was considered to be mainly due to an increase in the zinc concentration of seawater.

The Pummerer rearrangement of 1-deoxy-5-thioglucopyranose derivatives carrying acetonides at the C3,4-positions proceeded regioselectively at the C1 position by treating with TFAA in the presence of pyridine. Studies employing deuterium-labelled derivatives revealed that the reaction was induced by E2 1,2-elimination of trifluoroacetic acid of the trifluoroacetoxy sulfonium intermediate. This methodology was applied to the synthesis of an isomaltotriose derivative consisting of 5-thioglucopyranoside units.

The Pummerer rearrangement of 3,4-O-isopropylidene-1-deoxy-5-thiopyranose oxide derivatives took place at the C1 position regioselectively to give the corresponding 5-thiopyranoses. The reaction mechanism of this reaction is also discussed.

Polarization measurements of the Balmer α line of a beam emission are performed using a newly developed four-polarizer optical system on the JIPP T-IIU tokamak. Poloidal magnetic field profile in a plasma is obtained successfully in current ramp-up experiments. Electron density dependence of the relative emissivity of σ and π components in the motional Stark spectra is also investigated experimentally. The results suggest that the relative emissivity is independent of the electron density in the range of 2 × 1019-9 × 1019 m−3.

A heavy ion beam probe (HIBP) has been used as a reliable method to measure the plasma potential and its fluctuation in a magnetically confined fusion plasma. On the large helical device (LHD) an Au+ beam produced by a 3 MV tandem acceleration system will be used. It is necessary to optimize the charge fractions and minimize the energy broadening of the Au+ beam. Charge fractions can be calculated from electron loss and electron capture cross-sections. It is predicted that the optimum gas thickness for Au+ beam production is about 4 × 1014 cm−2. The broadening due to electron stripping is calculated to be several electronvolts and does not depend on the target mass. The energy straggling due to multiple collisions at the optimum target thickness can be calculated theoretically taking the lower limit of the impact parameter into account. Consequently, the total energy width of the Au+ produced by a tandem system might be about 100 eV.

In the National Institute for Fusion Science, a large helical device (LHD) is under construction, with the objectives of understanding the physical phenomena and behaviors of a magnetically confined high temperature plasma, and of obtaining basic data which can be extrapolated to a reactor-relevant plasma in a helical system. Superconducting coils with pole number l = 2. pitch number m = 10 and major radius R = 3.9 m produce a steady state helical magnetic field for confinement, together with poloidal coils. The magnetic field strength on the axis will be 3.0 T in the phase I experiment and 4.0 T in the phase II experiment. The plasma major radius of the LHD is 3.75 m and the averaged plasma radius is 0.6 m. The plasma volume will be about 30 m3. A plasma will be produced and heated by electron cyclotron heating, and heated with neutral beam injection and ion cyclotron resonance frequency heating. Three-dimensional diagnostics should be provided for helical systems, because the elliptic plasma cross-section rotates poloidally along the magnetic axis, and has no axisymmetry in comparison with tokamaks. It is also planned to produce a steady state plasma in the LHD. Therefore, the plasma diagnostics for the LHD have various features that are different from those in conventional tokamaks. The potential distribution in the plasma is an important quantity to be measured in a hellical system, because it is related to the plasma confinement. Proper functioning of the diverter is vitally important in a long-pulse machine. Divertor diagnostics are being examined with special precautions. Among various diagnostic developments carried out so far, a multi-point Thomson scattering system with high time and space resolution, a multi-channel far-IR laser interferometer and heavy ion beam probing will be explained in detail, after presenting details of the design principle, general description and a future plan for plasma diagnostics in the LHD.

A low energy (0.2–3 keV) fast neutral lithium beam source based on a glassy β-eucryptite Li+ source was developed for high spatial resolution (0.5 cm or less) density profile measurements in edge plasmas of tokamaks and stellarators. A 10-fold higher Li+ emission was obtained from this source as compared with the traditionally used pasty sources. Space charge effects became important for the ion beam propagation at such low energies, requiring careful beam control between the accelerator and the neutralizing section. In spite of this shortcoming, an approximately 40 μA cm−2 equivalent current Li0 beam at about 2 keV was obtained.

Asymmetry of the motional Stark spectrum is caused by large angular divergence of an injected natural beam. To avoid this difficulty caused by the spectrum asymmetry, only the σ component is used to determine the pitch angle in the case of a high magnetic field with an optical system that contains two polarizers tilted ± 45° with respect to the horizontal direction. It is predicted that the pitch angle could be measured with an accuracy better than 0.2°.

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.

The feasibility of a heavy ion beam with a tandem acceleration system for plasma potential measurement has been examined. A plasma-sputter-type ion source which produces an Au/sup -/ beam with an energy width as small as 6 eV and a reasonably small emittance of /spl pi/ mm-mrad (MeV)/sup 1/2 /, can be used for this purpose. Suitable target gas thickness for a charge exchange is estimated to be less than 10/sup 15/ atom/cm/sup 2/ at the 3 MV terminal voltage. >

Negative sodium ions (Na − ) were extracted from a small multi-cusp ion source. A steady state sodium plasma was produced by primary electrons in a sodium gas evaporating from a metal sample placed in the discharge chamber. The Na − current density of 1.5 μA/cm 2 was obtained from a single aperture of 1.5 mm diameter at relatively low discharge power of about 0.4 W and filament power of 50 W. Extraction characteristics were studied by changing the plasma electrode bias. The extracted Na − current showed a dependence on the bias voltage similar to that of H − or Li − volume production.

A gas chromatographic procedure has been developed for determination of chlordanes in environmental samples such as soil. The basis of the method is the conversion of many of these chlorinated C10 hydrocarbons into a single partial dechlorinated product, which is determined by gas chromatography with an electron capture detector. Soil is extracted with hexane. The extract is cleaned up on a Florisil cartridge and dechlorinated with Zn/HCl. The dechlorinated compound is injected into a gas chromatograph and chlordanes determined as one partially dechlorinated compound. The detection limit in this method is 0.002 μg/g. The coefficient of variation was 3.2% for soil samples while the average recovery was 94.3%. Although capable of determining only 4, 7-methanoindanes, which comprise more than 80% of the chlordanes, the significance of the method is recognized as the first means of screening for chlordanes. To date application has been made only to soil samples, but it is believed that with selection of the proper solvent for extraction, the method can be more broadly applied to samples such as food and biological samples.

In the next large tokamak facility such as the International Thermonuclear Experimental Reactor (ITER), the ion cyclotron range of frequency (ICRF) heating is one of the major techniques to heat the plasma. Due to the existence of the resonance peak for the D-T fusion reaction around 100 keV, the neutron yield of ICRF heated D-T plasma might decrease due to the growth of a high energy tritium ion tail when the temperature of the tail component exceeds ∼ 150 keV. On the contrary, the peak width of the D-T neutron spectrum increases monotonically as the tail temperature increases. 'Therefore, the neutron spectrum measurement could be a useful tool for monitoring the effect of ICRF heating on D-T fusion plasma. In this paper, the necessary performance of a neutron spectrometer will be discussed.

Dynamic change of a negative‐ion production surface in an ion source due to cesium introduction and plasma ion bombardment has been studied by simultaneous measurements of photoelectron current by laser irradiation and negative‐ion current. Strong dependences of production rates for negative ions by desorption (H−) and by sputtering (Au−) on the work function monitored by photoelectron current were observed. Peaks on mass spectra corresponding to He− were observed only when the monitoring signal indicated that the work function of a molybdenum‐cesium surface was near the minimum.

The magnetic probe is one of the important basic diagnostic techniques on a tokamak. With an increase in the duration of plasma sustainment, it is urged to develop a technique which can measure the steady state magnetic field, in order to determine the magnitude and the position of the plasma current in a long pulsed tokamak such as ITER. The probe, however, should endure high flux of neutron as well as heat from the fusion plasma. It is also necessary to place the diagnostic equipments as remote as possible.

Diatomic negative ions of Na(Na2 -) are extracted with atomic negative ions of Na(Na-) from a low-temperature Na plasma. The extracted currents of these negative ions are experimentally measured as functions of discharge parameters and wall temperatures. The measured extraction characteristics are discussed by comparing the results with those of negative hydrogen and negative lithium ions extracted from the corresponding plasmas. The maximum current ratio of Na2 - to Na- for a wall temperature below 235°C is on the order of 0.01, much smaller than that obtained in the sputtering experiment.

A heavy neutral beam probe was developed for simultaneous measurements of local space potential and density fluctuations in a plasma. It was applied to both electron cyclotron heated (ECH) and radio frequency heated (RF) plasmas in the bumpy torus NBT-1M, and the feasibility of this method was successfully demonstrated by observing a low frequency m=1 interchange mode which was rotating poloidally at a frequency near the E×B drift frequency. It was shown that use of this probe results in extension of the range of fluctuation measurement by beam probe technique to relatively low temperature plasmas. It is applicable to a plasma with a strong RF field with which Langmuir probes cannot be used.

The energy distribution of Au- extracted from a plasma-sputter type negative ion source was measured. The energy spread ΔE, which was defined as the FWHM of the observed negative ion energy distribution, increased with increasing target voltage (V t). When V t was about 280 V, the energy distribution agreed well with the Thompson-Sigmund (T-S) theory. For values of V t less than 280 V, the high-energy component in the distributions fell off faster than those predicted by the T-S theory. This effect was exaggerated as V t was further decreased. The ΔE for V t below 280 V are less than 10 eV, which seems to be sufficiently small for application to a heavy ion beam probing (HIBP) method.

A method to measure the work function of the target surface in a plasma-sputter-type negative ion source has been developed. The method can determine the work function by measuring the photoelectric current induced by two lasers (He-Ne, Ar+ laser). The dependence of Au- production upon the work function of the target surface in the ion source was studied using this method. The time variation of the target work function and Au- production rate were measured during the cesium coverage decrease due to the plasma ion sputtering. The observed minimum work function of a cesiated gold surface in an Ar plasma was 1.3 eV. At the same time, the negative ion production rate (Au- current/target current) took the maximum value. The negative ion production rate indicated the same dependence on the incident ion energy as that of the sputtering rate when the work function was constant.

A high-temperature radiation source has been developed for the absolute calibration of diagnostic instruments for measuring electron cyclotron emission from high-temperature plasmas. The source has a radiation area of φ 150 mm and can be heated up to 500°C. The measured emissivity of the source is close to unity in the spectral region between 200 and 500 GHz. The grating polychromator has been calibrated using the radiation source developed. The obtained temperatures agree with those by the pulse height analysis of soft X-rays and Thomson scattering measurement within 10%.

Spectroscopic and bolometric measurements with spatial and temporal resolution show that large radiation loss brings about the decrease in electron and ion temperature and plasma energy. Regarding emissivity in a core plasma, the result by bolometric measurements well agrees with that estimated from impurity abundance and radiative cooling rates. Carbon limiters have an effect to suppress the radiation loss for Ohmic plasma, but is insufficient for ICRF heated plasma. The main contribution to radiation loss may be attributed to Fe impurity released from the ICRF antennae, the Faraday shield and vacuum vessel. By making carbonization, the Fe impurity is suppressed to a low level ( n Fe / n e ∼0.03%) and the radiation loss is reduced to P rad /( P OH + P fr )∼20%. This clearly supported by the observation of Z eff (3.9→1.2).

A new method based on the laser-induced fluorescence method has been developed to measure the spatial electron density distribution in plasmas. The local electron density can be determined by observing the intensity ratio of the laser- to the collision-induced fluorescence. A spatial electron density distribution of a helium plasma (Te approximately 6 eV, ne:1011-12 cm-3) has been determined by observing the He(31P to 21S) laser-induced fluorescence and the He(31D to 21P) collision-induced fluorescence resulting from the He(31P to 31D) process due to collisions with electrons. The comparison of the result with that of a conventional method proves this new method is of practical use in the space-resolved measurements of plasma electron density.

Cross sections for one-electron capture by highly stripped ions of Be, B and C from H 2 and Ar are measured at low energies below 10 keV. The cross sections are nearly independent of the collision energy investigated. The distinct oscillation with incident ionic charge q in the cross sections are observed.

A ceramic secondary electron multiplier (SEM), Ceratron, was used to study impairment of the SEM performance due to adsorbed tritium, its decontamination, and the applicability of the SEM to measure tritium pressure. The background level of the SEM increased significantly, up to its counting limit, due to tritium adsorption. Heating it to 300°C in vacuo and/or in the presence of reactive gases such as D2 and CO at 1 × 10−4 Pa was not effective to decontaminate the SEM, whereas photon irradiation was extremely powerful for the decontamination. The tritium (HT) pressure in a range of 1 × 10−6−1 × 10−3 Pa could be measured with no significant impairment of the SEM performance with the aid of photon irradiation. It is revealed that a particle flux as low as 1 particle/s will be able to measure in the presence of tritium if suitable photon sources are installed in the systems.

Spatially resolved Kα lines of Fe XII–XVII and Kβ lines including their satellite lines of Ti VI–XIII from a vacuum spark were first measured using a Johann type crystal spectrometer with high resolution. The Fe Kα lines are shifted to the long-wavelength side of the Fe II Kα lines for some spatial locations, confirming calculated wavelengths. The transition energies of the Ti VI–XIII Kβ lines are determined and some weak satellite lines are first found.

Data of JIPP T-II ICRF heating experiments are presented. The experiment covers three typical cases: the low-concentration hydrogen minority case, the high-concentration hydrogen minority case, and the 3He-minority case. The best heating efficiency is obtained for the 3He-minority case. It is shown through power balance analysis that the two H-minority cases are different in the wave energy deposition profile. The difference is explained by the presence of a local cavity mode in the high-concentration minority case. The ion temperature stops rising at a power density level of 0.65 W-cm−3 for the hydrogen minority experiments. No such deterioration is found in the case of the 3He minority experiment up to a power density level of 0.45 kW-cm−3. This is the maximum possible to attain within the maximum power injection (180 kW) up to which the experiment is conducted. An analytic solution of the Fokker-Planck equation is derived in order to interpret the deterioration of the heating efficiency.

An HCN laser scattering technique is employed for detecting an electrostatic wave excited by ICRF heating on the JIPP T-IIU tokamak. The frequency spectra and wavenumber of the excited wave were observed during the heating. The measured wave is consistent with the theoretically estimated wave dispersion of the ion Bernstein wave which is mode-converted from the fast wave in the vicinity of the ion-ion hybrid resonance layer. The influence of MHD activity on the mode-converted ion Bernstein wave is examined. When the MUD activity grows and the plasma becomes unstable, the scattered signal from the ion Bernstein wave decreases, being accompanied with large fluctuations.