D. Araki

H. "Muta

T. Tanaka

T." Muroga

Y. Hishinuma

National Institute for Fusion Science (NIFS-Repository)

    Atomic and molecular processes play an important role in fusion plasmas. The cross section database for collision processes including the elements consisting the plasma facing materials are crucial demands to model the transport of eroded atoms and molecules. Considerable number of experimental cross section data for atomic and molecular collisions has been reported, since the cross-section data concerning atomic and molecular processes are important in the understanding of the fundamental physics of atomic and molecular collisions, which is the fundamental knowledge in many fields such as electron and ion driven processes in the Earth and planetary phenomena, radiation chemistry, gaseous discharges, weak and strong plasmas, and so on. Due to its importance, theses cross-section data are also compiled in the atomic and molecular databases around the world, and can be accessed online. The Japanese National Institute of Fusion Science, NIFS, provides one of the most relevant online databases on atomic and molecular cross sections in numerical data and bibliographic information. The database AMDIS for electron collisions and CHART for heavy particle collisions, respectively, were constructed over decades ago, and have been continuously updated from time to time. There also are databases for electron collisions and heavy particle collisions with molecules, so called AMOL and CMOL respectively. Data compilation and evaluation of these databases at NIFS have been continuously proceeding.  The present working group continuously supports the update of the atomic and molecular databases of NIFS by comprehensive data compilation of atomic and molecular cross sections. The collaborations of updates and extension for these NIFS atomic and molecular database had been continuously proceeding by selecting topics, such as atomic process with high Z elements, which were relevant for the LHD peripheral plasma.1) The collaboration also worked for the comprehensive data mining and compilation of atomic and molecular cross sections for the atomic and molecular processes including hydrogen isotopes and small hydrocarbons, since it was found that atomic and molecular data for electron impact and heavy particle impact cross section data on hydrogen isotopes and hydrocarbons are the urgent issue, during the previous collaboration for the collection and compilation of atomic and molecular data for high Z elements.   In the present collaboration, a comprehensive data mining and compilation of atomic and molecular cross sections for light elements of the 2 nd period such as Li, Be, B, C, N, O, F and Ne have been attempted. Electron impact cross section data and heavy particle impact cross section data for small atoms and molecules such as hydrogen, hydrogen isotopes, nitrogen, oxygen, hydrocarbons, Water and Carbon Oxide have been continuously surveyed in our previous collaboration and stored into the database, up to year 2000.2) However, new experimental as well as theoretical data for various processes by electron impact and heavy particle impact on these atoms and molecules have been reported from since we have carried out data survey. A complete survey for the existing literature and extraction of the cross section data sets were carried out in the present project.  In addition to the survey for the cross section data in the literature, we also have conducted a new measurement on electron - atom collision cross sections in the energy region from 20 eV down to very low energies with very high energy resolution.3,4,5) Our results resolved a number of issues in the literature and assessed various published theoretical results. We also have validated the theoretical electron impact cross section of He which has been regarded as a "standard" cross sections, to which a majority of experimental cross sections for atoms and molecules reported in the literature were normalized.     1) Kitajima M. et al. : NIFS-DATA, to be published. 2) Kimura M. et al. : NIFS-DATA-98 (2006) 3) Kurokawa M. et al. : Phys. Rev. A 84, 062717 (2011) 4) Kitajima M. et al. : Eur. Phys. J. D, (2012) 130. 5) Shigemura K. et al. : Phys. Rev. A 89, 022709 (2014)   In a fusion reactor design, distance between core-plasma and superconducting coils is one of important factors to decide a reactor size, magnetic field strength for plasma confinement etc. To reduce the distance, a thinner radiation shield layer with high density neutron shielding materials must be installed in a reactor. Metal hydrides, such as titanium, zirconium, and vanadium hydrides, are focused as the shielding material because they can include higher density of hydrogen atoms than liquid hydrogen. It is difficult to fabricate the bulk non-crack metal hydride because of the brittleness and ~20 % of volume change in the hydrogenation. Additionally, large amount and high accuracy of dimension are needed as the hydride shielding materials in fusion reactor. In the present study, to simplify the fabrication process, we tried to make dense titanium and zirconium hydride pellets by cold-pressing from their powders. In this case there is a concern about reduction of the thermal conductivity due to the low-density and weak contact between the particles. Low thermal conductivity raises the operation temperature and causes the hydrogen desorption, therefore the thermal conductivity of hydride pellets should be examined.  Commercial H-titanium hydride powder (Aldrich, 99 % purity) was used as a starting material. The powder was pelletized by cold-pressing with pressure of 50 MPa ~ 910 MPa. The density was calculated from the weight and dimensions. The thermal diffusivity was measured by laser flash method using Netzsch LFA457. Using literature data of heat capacity 1), thermal conductivity, N, was estimated by N = DCPd,where D, CP, d were thermal diffusivity, heat capacity and sample density.       Fig. 1 shows a SEM image of H-titanium hydride pellet. The pressure at cold-pressing is 910 MPa. The particles appear to deform by the pressing and 90 % of the theoretical density is achieved by the condition. It is noted that the titanium becomes softened by hydrogen 2), which might provide the high density only by the cold-pressing. The relation between the relative sample density and pressure is shown in Fig. 2 together with the result of H-zirconium hydride. With increasing the pressure, the sample density increases linearly. For both titanium and zirconium hydrides, 90 % of theoretical density was achieved by cold-pressing.      The estimated thermal conductivity of H-titanium hydride and H-zirconium hydride are shown in Fig. 3. The value increases with the density. The temperature dependence is relatively weak, which indicate the thermal conduction was dominated by the electrons. With comparison to the thermal conductivity: ~20 Wm-1K-1 for the bulk sample 3), the fabricated sample shows comparable value of 14 Wm-1K-1 at room temperature. It attributes to the strong contact between the particles. The titanium hydride structure fabricated by cold-pressing can be a candidate of the shielding material in a fusion reactor. Fig. 1. SEM image of H-titanium hydride pellet.  Fig. 2. Relative sample density of H-titanium hydride and zirconium hydride pelletized by cold pressing.     Fig. 3. Temperature dependence of thermal conductivity of H-titanium hydride and H-zirconium hydride. 1) Yamanaka, S. et al., J. Alloys Compd., 330-332 (2002) 99. 2) D. Setoyama, J. Matsunaga, H. Muta, M. Uno, S. Yamanaka, J. Alloys Compd, 381 (2004) 215–220. 3) D. Setoyama, J. Matsunaga, M. Ito, H. Muta, et al., J.Nucl. Mater., 344 (2005) 298–300. 㻜 㻞㻜㻜 㻠㻜㻜 㻢㻜㻜 㻤㻜㻜 㻝㻜㻜㻜 㻝㻞㻜㻜 㻝㻠㻜㻜㻡㻜㻢㻜㻣㻜㻤㻜㻥㻜㻾㼑㼘㼍㼠㼕㼢㼑㻌㼟㼍㼙㼜㼘㼑㻌㼐㼑㼚㼟㼕㼠㼥㻌㻔㻑㼀㻚㻰㻚㻕㻼㼞㼑㼟㼟㼡㼞㼑㻌㻔㻹㻼㼍㻕㻌H㻙㼆㼞㻴㻞㻌㼀㼕㻴㻞㻞㻡㻜 㻟㻜㻜 㻟㻡㻜 㻠㻜㻜 㻠㻡㻜 㻡㻜㻜 㻡㻡㻜 㻢㻜㻜 㻢㻡㻜㻜㻞㻠㻢㻤㻝㻜㻝㻞㻝㻠㼀㼕㻴㻞㻌㻡㻜㻌㻹㻼㼍㻌㻝㻜㻜㻌㻹㻼㼍㻌㻞㻜㻜㻌㻹㻼㼍㻌㻠㻜㻜㻌㻹㻼㼍㻌㻥㻝㻜㻌㻹㻼㼍㼀㼔㼑㼞㼙㼍㼘㻌㼏㼛㼚㼐㼡㼏㼕㼠㼕㼢㼠㼥㻌㻔㼃㼙㻙㻝 㻷㻙㻝 㻕㼀㼑㼙㼜㼑㼞㼍㼠㼡㼞㼑㻌㻔㻷㻕㼆㼞㻴㻞㻌㻡㻜㻌㻹㻼㼍㻌㻝㻜㻜㻌㻹㻼㼍㻌㻞㻜㻜㻌㻹㻼㼍㻌㻠㻜㻜㻌㻹㻼㼍㻌㻝㻞㻞㻜㻌㻹㻼㼍353§34. Applicability Study of Hydride Materials for Neutron Shielding in a DT Fusion ReactorMuta, H., Araki, D. (Osaka Univ.),  Tanaka, T., Hishinuma, Y., Muroga, T.

Applicability Study of Hydride Materials for Neutron Shielding in a DT Fusion Reactor

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Applicability Study of Hydride Materials for Neutron Shielding in a DT Fusion Reactor

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