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Hirooka Y.,Japan National Institute for Fusion Science | Zhou H.,Graduate School for Advanced Studies | Ono M.,Princeton Plasma Physics Laboratory
Fusion Engineering and Design | Year: 2014

For improved core performance via edge plasma-wall boundary control, solid and liquid lithium has been used as a plasma-facing material in a number of confinement experiments over the past several decades. Unfortunately, it is unavoidable that lithium is saturated in the surface region with implanted hydrogenic species as well as oxygen-containing impurities. For steady state operation, a flowing liquid lithium divertor with forced convection would probably be required. In the present work, the effects of liquid stirring to simulate forced convection have been investigated on the behavior of hydrogen and helium recycling from molten lithium at temperatures up to ∼350 °C. Data indicate that liquid stirring reactivates hydrogen pumping via surface de-saturation and/or uncovering impurity films, but can also induce helium release via surface temperature change. © 2014 Elsevier B.V. Source

Hirooka Y.,Japan National Institute for Fusion Science | Zhou H.,Graduate School for Advanced Studies
Fusion Science and Technology | Year: 2014

The first wall of a magnetic fusion DEMO reactor serves to separate the edge plasma from breeding blanket, the latter of which is required to operate at elevated temperatures. To minimize the thermo-mechanical stress, the wall thickness is often limited to be less than 1 cm. As a result, the first wall is subjected to hydrogen isotopes permeation in the two opposite directions via plasmadriven permeation (PDP) by D+ (or D0) and T + (or T0) in the edge plasma region and via gas-driven permeation (GDP) by T2 bred in the blanket. In the present work, the bi-directional hydrogen permeation behavior through a candidate first wall material, F82H, has been studied, using a laboratory-scale plasma device. Experimental data indicate that GDP tends to dominate the overall hydrogen isotopes transport. The effects of surface roughness and contamination on PDP have been investigated. Also, a one-dimensional diffusion code has been used to simulate bi-directional PDP and GDP under reactor-relevant conditions where multiple hydrogen isotopes flow through the first wall. Source

Kuzmin A.,Kyushu University | Zushi H.,Kyushu University | Takagi I.,Kyoto University | Sharma S.K.,Indian Institute for Plasma Research | And 17 more authors.
Journal of Nuclear Materials | Year: 2015

Abstract Hydrogen wall pumping is studied in steady state tokamak operation (SSTO) of QUEST with all metal plasma facing materials PFMs at 100 °C. The duration of SSTO is up to 820 s in fully non-inductive plasma. Global gas balance analysis shows that wall pumping at the apparent (retention-release) rate of 1-6 × 1018 H/s is dominant and 70-80% of injected H2 can be retained in PFMs. However, immediately after plasma termination the H2 release rate enhances to ∼1019 H/s. In order to understand a true retention process the direct measurement of retention flux has been carried out by permeation probes. The comparison between the evaluated wall retention and results from global analysis is discussed. © 2014 Elsevier B.V. Source

Kuriki M.,Hiroshima U. | Iijima H.,Hiroshima U. | Masumoto Y.,Hiroshima U. | Isoyama G.,Osaka U. | And 7 more authors.
IPAC 2011 - 2nd International Particle Accelerator Conference | Year: 2011

Status of RF processing of L-band RF gun at KEK-STF (Superconducting Test Facility) is presented. A 1.3 GHz normal conducting RF photo-injector has been prepared for KEK-STF, where Super-conducting technology is being developed for ILC (International Linear Collider). MEXT Quantum Beam project, high brightness X-ray generation by inverse laser Compton scattering, also will be carried out at STF. In both cases, the high intensity electron beam in multi-bunch and long macro-pulse up to 0.9ms has important roles. The RF gun cavity has been fabricated by DESY-FNAL-KEK collaboration and the first high power RF processing has been carried out in 2009, but a large amount of dark-current (280μA at 28 MV/m) was observed. In order to cure the problem, the cavity surface was treated by ethanol rinsing to suppress the dark current. The second high power RF processing was performed in January 2011. The dark-current was decreased by an order of magnitude, down to 18μA at the same condition. For each processing, RF power was up to 1.7 MW, which was limited by the power source. The real operation will be made at 3.5 MW input power with a new power source. The third high power RF processing is scheduledwith this newpower source from September 2011. Copyright © 2011 by IPAC'11/EPS-AG. Source

Muroga T.,Japan National Institute for Fusion Science | Nagasaka T.,Japan National Institute for Fusion Science | Zheng P.F.,Graduate School for Advanced Studies | Zheng P.F.,Southwestern Institute of Physics | And 3 more authors.
Journal of Nuclear Materials | Year: 2013

Dislocation evolution during thermal creep deformation was investigated at 1023 K for V-4Cr-4Ti alloys with various thermal and mechanical treatments. Changes in the density and Burgers vector of dislocations were examined with various materials and experimental variables (e.g., cold work introducing dislocations, thermal aging introducing high density of Ti-rich precipitates, applied stress, and creep deformation levels). The Burgers vector analysis showed that, in the annealed specimens, dislocations induced by the thermal creep were predominantly of a/2〈1 1 1〉 type. The densities of a〈1 0 0〉 and a/2〈1 1 1〉 type dislocations were comparable for the cold worked V-4Cr-4Ti, but the fraction of a/2〈1 1 1〉 type dislocations increased with the creep deformation. Similar changes to the Burgers vector fraction were observed for specimens with a high density of precipitation prior to the cold work. On the other hand, cold work followed by aging (i.e., strain aging) was effective in keeping dislocation structures during the creep deformation. © 2013 Elsevier B.V. All rights reserved. Source

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