Hironobu Niimi

High performance tokamak experiments with a ferritic steel wall on JFT-2M

Compatibility between the plasma and low activation ferritic steel, which is a candidate material for fusion demonstration reactors, has been investigated step by step in the JFT-2M tokamak. We have entered the third stage of the Advanced Material Tokamak EXperiment (AMTEX), where the inside of the vacuum vessel wall is completely covered with ferritic steel plates ferritic inside wall (FIW). The effects of a FIW on the plasma production, impurity release, the operation region, and H-mode characteristics have been investigated. No negative effect has been observed up to now. A high normalized beta plasma of βN ~ 3, having both an internal transport barrier and a steady H-mode edge was obtained. A remarkable reduction in ripple trapped loss from 0.26 MW m−2 (without ferritic steel) to less than 0.01 MW m−2 was demonstrated by the optimization of the thickness profile of FIW. A code to calculate fast ion losses, taking into account the full three-dimensional magnetic structure was developed, and values obtained using the code showed good agreement with experimental results. Thus, encouraging results are obtained for the use of this material in the demo-reactor.

Photochemical Transformation of Molecular Crystals into Devices

Title Photochemical Transformation of Molecular Crystals into Devices Author(s) Naito, T.; Sugawara, H.; Inabe, T.; Miyamoto, T.; Niimi, H.; Asakura, K. Citation Multifunctional Conducting Molecular Materials, pp.181-184 Issue Date 2007 Doc URL http://hdl.handle.net/2115/21517 Rights T. Naito, H. Sugawara, T. Inabe, T. Miyamoto, H. Niimi and K. Asakura, Photochemical Transformation of Molecular Crystals into Devices, in Multifunctional Conducting Molecular Materials, ed. Gunzi Saito et al., pp.181-184, Royal Society of Chemistry ‒ Reproduced by permission of The Royal Society of Chemistry. Type bookchapter (author version) File Information MCMM2007.pdf

Ag L(3)-edge X-ray absorption near-edge structure of 4d(10) (Ag(+)) compounds: origin of the edge peak and its chemical relevance.

A peak appearing at the L(2,3) X-ray absorption edge often provides the number of empty d states of the X-ray absorbing atoms. Ag(+) compounds have a d(10) state (no d empty states) but show a small peak at the edge. In this research, we systematically studied the edge peak of Ag(+) compounds to understand its origin on the basis of the molecular orbital picture and to obtain a relation of the edge peak intensity to chemical and physical quantities. The edge peak can be formally assigned to the transition from 2p to 5s enhanced by the s-d hybridization. The peak intensity has a negative correlation with a coordination charge but has a positive correlation with the strength of the covalent bond, which is in the reverse order to the other d(n) (n < 10) elements.

Behaviour of compact toroid injected into an external magnetic field

The interactions of a compact toroid (CT) plasma with an external magnetic field and a tokamak plasma have been studied experimentally on the FACT and JFT-2M devices. Fast framing camera and soft X ray emission profile measurements indicate shift and/or reflection motions of the CT plasma. New electrostatic probe measurements indicate that the CT plasma reaches at least up to the separatrix for discharges with toroidal field strengths of 1.0-1.4 T and that there exists a trailing plasma behind the CT. A large amplitude fluctuation on the ion saturation current and magnetic coil signals is observed. Power spectrum analysis suggests that this fluctuation is related to magnetic reconnection between the CT plasmoid and the toroidal field. The CT, including much of the trailing plasma, may be able to move across the external magnetic field more easily in the drift region of the injector owing to the Hall effect.

Aberration-corrected multipole Wien filter for energy-filtered x-ray photoemission electron microscopy

The aberration of a multipole Wien filter for energy-filtered x-ray photoemission electron microscopy was analyzed and the optimized Fourier components of the electric and magnetic fields for the third-order aperture aberration corrections were obtained. It was found that the third-order aperture aberration correction requires 12 electrodes and magnetic poles.

Observation of element-specific energy-filtered X-ray photoemission electron microscopy images of Au on Ta using a wien filter type energy analyzer

We have shown the possibility of a Wien filter as an energy analyzer for the energy-filtered X-ray photoemission electron microscopy (EXPEEM) by obtaining images of Au islands on a Ta substrate using an inner shell photoelectron excited by an X-ray with a photon energy of 2300 eV. When the photoelectron with kinetic energy of nearly 0 eV was selected, brighter Au islands were observed. When the kinetic energies of photoelectrons passing the Wien filter are set at those of Au 3d5/2 and Ta 3p3/2 photoelectrons, the Au and Ta regions appeared brighter, respectively, indicating that the chemical imaging was successful using a high energy X-ray and a Wien filter energy analyzer.

Energy Filtered X-Ray Photoemission Electron Microscopy

Abstract This chapter reviews photoemission electron microscopy (PEEM) and energy filtered X-ray PEEM (EXPEEM) that provides us the chemical mapping of the surface. We describe the history and the principle of PEEM and EXPEEM. We focus on the Wien filter type energy analyzer with the third order aberration corrected. In situ observation of surface reactions and chemical mapping of soft materials are discussed as examples of the PEEM and EXPEEM applications to chemistry.

Photochemical Method of Device Fabrication Starting from Molecular Crystals

The conductivity of a silver salt of N,N′-dicyanoquinonediimine irreversibly varied in approximate proportion to an illumination of a wide range of wavelengths. Depending on the illumination conditions, four different states (β, γ, δ, and ϵ) were obtained with different structures. The β structure is in particular important, where the formal charge of the N,N′-dicyanoquinonediimine molecules continuously decreased to −0.4–−0.35 with retaining the crystal structure, when we kept the temperature <155°C during the illumination. The non-illuminated area of the sample retained its original electrical property with a well-defined interface, which enabled a fabrication of a junction-structure in the single crystal.

A New Collinear-Type Energy-Filtered X-ray Photoemission Electron Microscope Equipped with a Multi-Pole Aberration-Corrected Air-Core Coil Wien Filter

We present the prototype of a new, collinear-type energy-filtered X-ray photoemission electron microscope (EXPEEM) using a multi-pole, aberration-corrected air-core coil Wien filter (WF) analyzer. We have designed the new WF with 12-pole electrodes and magnetic poles to reduce spherical aberrations and fringe effects. We assess the performance of the WF using an electron energy analyzer for PEEM. The sensitivity is enhanced 10?100 fold compared with a simple, two electrodes plus two magnetic poles type WF. Cu 2p3/2 and Au 4f7/2 photoelectron energy selected images are obtained in a laboratory-scale source within several minutes. The energy and spatial resolutions of our prototype EXPEEM are estimated to be 3 eV and 7 ?m, respectively.