Susumu Amemiya

Analysis of the plasma-wall interaction in the Heliotron E device

The plasma-wall interaction (PWI) of the currentless plasmas with temperature To, Tio ≤ 1.1 keV, density Ne = (2–10)× 1013/cm3, and volume-averaged beta value of β

Investigation of environmental problems caused by studded tires of automobiles using PIXE

≤ 2% was investigated. We have observed that PWI took place mainly where the divertor field line intersected the chamber wall (called divertor traces). Boundary plasmas were measured with electrostatic probes, which showed the presence of the divertor region with the parameters in the range of Ned = 1010–1011/cm3 and Ted = 10–50 eV. Surface analysis techniques (ESCA, AES, and RBS) were applied to analyze the surface probes (Si, graphite and stainless steel) and the test pieces (SiC, TiC, and stainless steel), which were irradiated by plasmas for short and long times respectively.

Probe measurements for impurity transport in the scrape-off layer of JIPP T-II

Abstract The PIXE technique has been successfully applied to investigate the environmental problems caused by the studded tire of automobiles. The dust samples were collected on stacked filters in Sapporo and some other cities in Japan and Europe. PIXE measurements were performed using a 2 MeV proton beam. The results were compared with those of different cities. The main components of dust particulates were Al, Si, Ca, Fe and so on. The vertical distribution of dust concentration in the city of Sapporo was determined by PIXE in April and June. The concentration in April decreases exponentially with height from the ground. The effect of dust particulates due to studded tires is observed up to an altitude 60 m. On the other hand in June, the concentration on the ground is one-tenth of that in April, and it is almost unchanged with the distance in the vertical direction. The concentration of Ca in the dust particulates in the area where the studded tires are used increases by a factor of 2 to 4 in comparison with that in the ordinary soil.

Cross section measurements of (n,n') and (n,2n) reactions on zirconium and lead targets at 14.8 MeV.

Impurity transport processes in the scrape-off layer of the JIPP T-II device have been studied by a probe method. A cubical silicon probe was inserted and exposed to 20 identical tokamak discharges in the scrape-off region. Deposited impurities were analysed with use of AES, RBS and PIXE equipments. The main metallic impurities were molybdenum and iron whose deposition behavior was almost the same on any side of the probe, and their fluxes were observed to be 1.2 × 1013/cm2· discharge on the electron drift side and 5.2 × 1013/cm2· discharge on the ion drift side, respectively at the distance of 18.3 cm from the center line of the plasma. The mean transport energy of the impurities striking the probe surface was estimated from the depth concentration profile applying the LSS theory for iron as 90 eV on the electron drift side and 250 eV on the ion drift side, respectively. The e-folding length of the scrape-off plasma density was measured by the radial distribution of a deposited tantalum amount to be 0.64 cm on the electron drift side and 1.73 cm on the ion drift side, respectively.

Study on in-situ carbon coating in JIPP T-IIU

The cross sections for the reactions 90Zr (n, n′) 90mZr, 91Zr (n, n′)2n) 90mZr, 207Pb (n, n′) 207mPb and 208Pb (n, n′)2n) 207mPb for neutron energy of 14.8 MeV have been measured by means of the activation method. The cross sections were determined with reference to the known 27A1 (n, α) 24Na reaction cross section. Isotropically enriched isotopes 90Zr, 91Zr, 207Pb and 208Pb were used as target materials. The irradiations and the activity measurements were repeated 100 times using a fast pneumatic transport system. The following cross sections were obtained: 410±40 mb for 90Zr (n, n′) 90mZr, 775±65mb for 91Zr (n, 2n) 90mZr 160±23 mb for 207Pb(n, n′) 207mPb, 1,220±100 mb for 208Pb(n, 2n) 207mPb. From the results of the present work, the effective formation cross sections of 90mZr and 207mPb for natural Zr and Pb have also been estimated as 475±40mb and 900±80mb, respectively

Hydrogen isotope retention and impurity deposition of carbon based components used in JT-60U

The effectiveness of the in-situ carbon coating (carbonization) has been demonstrated to reduce the radiation loss by iron impurities during ICRF heating in the JIPP T-IIU tokamak. As a result of carbonization, the total radiation loss decreased down to one fifth of the RF power, which resulted in an increase in electrons and total stored energy compared with these conditions before carbonization. The thickness of the carbon layer was 300–900 A, and its toroidal uniformity was within a factor of 3, although only one anode and one gas-inlet were used. A thin carbide layer is formed between the C-film and the stainless steel substrate with carbonization at room temperature. The hydrogen concentration is 40–50 at.% in the carbon layer. Deposition of carbon was observed on window materials. The deposition rate was relatively less on electrical insulators compared to the deposition rate on metals.

Gamma-Ray Spectroscopy of76As

Abstract Various types of carbon based components, such as isotropic graphite, carbon fiber composite (CFC-2D felt type) and B 4 C-overlaid CFC/graphite were used for divertor and first wall tiles in JT-60U. Surface analysis of tiles exposed to discharge shots in JT-60U, was performed using MeV region ion beam. The retention of deuterium for each tile was distributed between ∼ 6 × 10 20 and ∼ 6 × 10 21 m −2 . Highest deuterium retention was observed on the outboard, lower part of first wall tiles. Metallic impurity measurement was performed by X-PIXE. The dominant species were Fe, Cr, Ni, Cu, Mo and Zn of which total concentration as high as 10 21 m −2 . This value is one order of magnitude smaller than that of JT-60. Highest oxygen concentration examined by RBS was observed on the B 4 C converted graphite tile. Carbon tile containing B 4 C is shown to be useful for oxygen gettering compared with an other.

PIXE analysis of atmospheric aerosols collected over Hungary and Japan

Decay of 76 As was investigated by using a Ge(Li) detector and Ge(Li)-NaI(Tl) coincidence methods. Sixteen new gamma-rays were observed and eleven of them were assigned in a proposed decay scheme. Four new levels were found at 2026.4, 2365.1 and 2514 keV. Spins and parities of levels at 2026.4, 2655.7 and 2669.8 keV were estimated from log ft values of beta transitions which fed these levels. Existences of 563.4 and 772.1 keV gamma-rays emitted from the 0 + and 4 + levels which were considered to be levels of two-phonon triplet states and observed by the coulomb excitation and the inelastic scattering experiments were confirmed. Characters of the 1691.5 and 1788.1 keV levels as three phonon states were discussed.

Application of PIXE to the study of nuclear fusion materials

Abstract The PIXE analysis of atmospheric samples collected over Hungary and Japan has been made to investigate characteristic features of the samples of Hungary and Japan, and to compare them. Samples were collected at Budapest, Debrecen, Szerencs, Palhaza in Hungary, and at Tokyo, Noma coast Aichi, Obara-mura Aichi (rural district), Mt. Rokko, in Japan. The PIXE analysis of the samples was made using a 2 MeV proton beam from a Van de Graaff accelerator at Nagoya University. Differences, specially in the concentration of lead, between samples collected in Hungary and Japan were observed.

Surface probe measurements of impurities and hydrogen isotopes in the Heliotron E device

Abstract The PIXE technique was applied to the analysis of impurity elements deposited on the surface probe and the fixed ring limiters of the JIPP T-II tokamak/stellarator fusion device. Various elements were identified as impurities contaminating the plasma discharge. Heavy elements were originated from the composite materials of a vacuum vessel and limiters. The particle flux of such heavy elements varied depending upon the direction of transport. The particle flux of iron and of molybdenum along the toroidal field was 5 × 10 13 atoms/cm 2 discharge, which was almost five times larger than another direction in the scrape-off plasma. Their deposition behavior was almost identical and suggested that the impurity source of molybdenum and iron should be at the same place in the experimental fusion device. However, light impurities such as aluminum and silicon showed different deposition behavior.