Akira Taniike

Characteristics of lithium thin films under deuterium ion implantation

Abstract To clarify characteristics of thin Li films as a plasma facing material, effect of modification of chemical composition of μm-thick deposited Li films introduced during the sample preparation and implantation with 1-keV deuterons on deuterium retention and thermal desorption properties is studied. Accelerator analysis has been employed to measure the thickness, the retention of D, H, O and C in the Li film, while thermal desorption spectroscopy has been utilized to investigate the chemical composition. The Li films exposed to moist atmosphere and subjected to D implantation show almost perfect isotope exchange from LiOH to LiOD. Carbon deposition during ion implantation is found to form a layer mixed with Li. With increasing the deposited amount of C, D2 desorption behavior approaches that of pure C.

Ion-irradiation induced hydrogen loss from polyethylene film

Degradation of a polymer under ion irradiation is investigated quantitatively. The loss of hydrogen atoms in polyethylene films under bombardment of various kinds of ions has been measured by directly monitoring recoil hydrogen atoms. Fluence dependence of the decrease in the hydrogen density is analyzed using a modified model based on that of M. P. de Jong, A. J. H. Maas, L. J. van Ijzendoorn, S. S. Klein, and M. J. A. de Voigt, J. Appl. Phys. 82, 1058 (1997). It is shown that the dependence is well explained by the present model with a hydrogen trapping reaction constant having hydrogen density dependence. It is found that the product of a bond cleavage probability squared and an ion track area is proportional to z4/E3, where z and E are the atomic number and energy of the projectile, respectively.

Adsorption of tributyltin by tributyltin resistant marine Pseudoalteromonas sp. cells.

The isolate, Pesudoalteromonas sp. TBT1, could grow to overcome the toxicity of tributyltin chloride (TBTCl) up to 30 microM in the absence of Cl(-) in the medium until the cells reached an exponential phase of growth. The viability, however, was reduced after the cells reached a stationary phase. The degradation products, such as dibutyltin (DBT) and monobutyltin (MBT), were not detected in the growth medium, indicating that the isolate has no ability to degrade TBT into less toxic DBT and MBT. Up to about 10(7.5) TBT molecules were adsorbed by a single cell. The observation of morphological changes with an electron microscope showed that the cell surface became wrinkled after exposure to the lethal concentration of 10 mM TBTCl. These results indicate that the resistance of the isolate toward the toxicity of TBTCl is not related to the unique cell surface, which seems to play an important role in preventing the diffusion of TBTCl into the cytoplasm.

Development of a double-charge exchange He− source

A dc-mode He− source of the double charge exchange type has been developed for the purpose of application to alpha-particle measurement. Because the optimum energy for the two-step two-electron capture process in a rubidium vapor was reported to be around 6 keV, the essential point of development is extraction of an intense He+ beam at relatively low energy. As the discharge current of the He+ ion source is increased, the focusing property deteriorates, and higher electrostatic field is required for extraction. A He− current of 0.07 mA is continuously obtained from a He+ beam extracted from a 6 mm diameter single hole. The conversion efficiency from He+ to He− is about 2%–3% in the energy region of 5–10 keV.

Accelerator analysis of tributyltin adsorbed onto the surface of a tributyltin resistant marine Pseudoalteromonas sp. cell.

Tributyltin (TBT) released into seawater from ship hulls is a stable marine pollutant and obviously remains in marine environments. We isolated a TBT resistant marine Pseudoalteromonas sp. TBT1 from sediment of a ship’s ballast water. The isolate (109.3 ± 0.2 colony-forming units mL−1) adsorbed TBT in proportion to the concentrations of TBTCl externally added up to 3 mM, where the number of TBT adsorbed by a single cell was estimated to be 108.2. The value was reduced to about one-fifth when the lysozyme-treated cells were used. The surface of ethanol treated cells became rough, but the capacity of TBT adsorption was the same as that for native cells. These results indicate that the function of the cell surface, rather than that structure, plays an important role to the adsorption of TBT. The adsorption state of TBT seems to be multi-layer when the number of more than 106.8 TBT molecules is adsorbed by a single cell.

Charge fractions and energy width of heavy ion beam probe for large helical device

Abstract 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.

RBS ANALYSIS OF DEUTERIUM DISTRIBUTION WITH COINCIDENCE DETECTION OF RECOIL PARTICLES

Abstract A novel analytical method of deuterium depth distribution is presented for a film target with thickness exceeding a few μm. The method is based on the Rutherford Backscattering Spectroscopy (RBS) combined with the Elastic Recoil Detection (ERD). The scattered protons are detected coincidentally with the recoil deuterons to eliminate protons scattered by substrate and impurity atoms. Energy of the coincident protons is then analyzed to deduce the deuterium distribution. Results of proof-of-principle experiments using a deuterated polyethylene film and a deuterium implanted titanium sample are presented, and effect of multiple scattering is discussed. The present method is applicable for targets with thickness of several μm which cannot be reached by conventional heavy-ion ERD using MV accelerators, and has an advantage that we can avoid deformation of hydrogen isotope distribution caused by irradiation of heavy ions.

Measurements and analysis of neutron flux distribution in UTR-KINKI

The neutron flux distributions in UTR-KINKI are comprehensively analyzed in terms of the Au activation reaction rate and compared with those calculated by SRAC-CITATION and MCNP4C. The vertical distribution at the central stringer is found to be a cosine-like one with a smaller FWHM by about 15%, which is in good agreement with both simulation results within an RMS deviation of 2.4% and 2.1%, respectively. However, the CITATION fails to predict the horizontal distribution and humps in the vertical distribution in the fuel tank (FT) just outside the fuel meat due to low energy neutrons moderated in the H2O reflector region. It is suggested that the method of homogenization of the fuel assembly should be optimized to have satisfactory agreement with the measured distributions. On the contrary, the MCNP reproduces well the vertical distribution within the experimental uncertainty of ±3% in the FT and the horizontal distribution within the error of ±10%. From a little asymmetry of the distributions measured in the FT, it is implied that perturbation of the low energy neutron flux due to control rods or voids for them could be appreciable, and should be taken into account in the calculations in order to have even better agreement with the measured distributions.

Enhanced Energy Recovery in a Secondary Electron Direct Energy Converter through Reduction of the Magnetic Mirror Effect

Abstract With an aim to improve the total efficiency of a D-3He nuclear fusion direct energy conversion system, a secondary electron direct energy converter (SEDEC) is proposed. The incident high-energy protons in an SEDEC penetrate a large number of foil electrodes aligned in the direction of the proton beam, and emitted secondary electrons are recovered. The results of the initial experiments showed that most of the secondary electrons flowed into anteroposterior electrodes and did not arrive at the electron collector located alongside and perpendicular to the direction of the proton beam. A magnetic field was introduced to push the electrons toward the electron collector, but it was not effective for energy recovery. This technical note analyzes the trajectories of electrons in the presence of the magnetic field and proposes and examines a revised arrangement of permanent magnets. The arrangement of the magnets along one side of the proton beam greatly improved the energy recovery; however, the recovery level was lower than that without magnets.

Basic Characteristics of Secondary Electron Emission from Foil Electrodes for New Energy Recovery Scheme of High Energy Ions in an Advanced Fusion

The new energy recovery method using secondary electron emission has been studied in order to improve energy recovery from high energy protons of fusion products in D-3He nuclear fusion generation. The model experiments were performed by using the tandem electrostatic accelerator and the basic characteristics were investigated. According to our results, for penetration aluminum is better as a target material than copper, H+ is better than He2+, and higher energy beam is better which agree with numerical calculations. A qualitative characteristic of secondary electron emission dependence on beam energy was also obtained.