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Journal Articles

Investigation of advanced divertor magnetic configuration for Demo tokamak reactor

Asakura, Nobuyuki; Shinya, Kichiro*; Tobita, Kenji; Hoshino, Kazuo; Shimizu, Katsuhiro; Uto, Hiroyasu; Someya, Yoji; Nakamura, Makoto; Ono, Noriyasu*; Kobayashi, Masahiro*; et al.

Fusion Science and Technology, 63(1T), p.70 - 75, 2013/05

 Times Cited Count:11 Percentile:22.55(Nuclear Science & Technology)

Design study of poloidal field coil (PFC) locations and current distribution for the advanced divertor in the Demo tokamak reactor was presented. Concept of the super-X divertor (SXD) for Demo reactor has an outer divertor leg longer than the conventional divertor, and it extends outboard to increase both the target wetted area and connection length to the outer target ($$L_{//}$$). Equilibrium calculation code, TOSCA, was developed by introducing two parameters, i.e. super-X null radius ($$R_{SX}$$) and a ratio of the poloidal flux at the super-X null to that at the separatrix ($$f_{SX}$$). Some SXD magnetic configurations with minimal number of PFCs located outside toroidal field coil (TFC) were Demonstrated. Locations of the divertor target were also investigated. It was found that the flux expansion can be increased up to 4-10 depending on the target location and $$f_{SX}$$, and that SXD has an advantage to increase $$L_{//}$$ with $$f_{SX}$$. Thus, the divertor plasma temperature is expected to decrease at the same upstream plasma density. On the other hand, large currents for the divertor PFCs were necessary. Other arrangements of PFCs such as (1) larger $$R_{SX}$$ and (2) inside TFC, can reduce the PFC currents.

Journal Articles

Resonant magnetic perturbation for ELM suppression with helical ferritic steel inserts in tokamak DEMO reactor

Takizuka, Tomonori*; Oyama, Naoyuki; Fukuda, Takeshi*

Fusion Science and Technology, 63(1T), p.64 - 69, 2013/05

 Times Cited Count:1 Percentile:85.59(Nuclear Science & Technology)

Edge localized mode (ELM) must be eliminated which enhances the erosion of divertor plates in the H-mode operation of tokamak reactors. Suppression of ELM has been experimentally achieved by the resonant magnetic perturbation (RMP) with multipartite coils. In a DEMO reactor with strong neutron flux, however, it is desired the coils near the first wall not to be put in. We propose an innovative concept of the RMP for tokamak DEMO reactors without installing coils but inserting ferritic steels of the helical configuration. Helically perturbed magnetic field is naturally formed in the axisymmetric toroidal magnetic field through the helical ferritic steel inserts (FSIs). The perturbation amplitude in the plasma pedestal region can easily be set above several 10$$^{-4}$$ of the toroidal field strength in the DEMO reactor condition, which is enough for the RMP to suppress ELM.

Journal Articles

Dual frequency ECRF system development for JT-60SA

Kobayashi, Takayuki; Isayama, Akihiko; Sawahata, Masayuki; Suzuki, Sadaaki; Terakado, Masayuki; Hiranai, Shinichi; Wada, Kenji; Sato, Yoshikatsu; Hinata, Jun; Yokokura, Kenji; et al.

Fusion Science and Technology, 63(1T), p.160 - 163, 2013/05

 Times Cited Count:6 Percentile:43.43(Nuclear Science & Technology)

A dual frequency electron cyclotron range of frequency system has been developed for JT-60SA, by which a second frequency (135 $$sim$$ 140 GHz) is generated in addition to the first frequency of 110 GHz. A development of a dual frequency gyrotron is a key to realize the dual frequency system. The second frequency was chosen to be 138 GHz from the above frequency range from the viewpoint of gyrotron design. In order to realize high-power ($$>$$ 1 MW) and long-pulse operation for both frequencies, we designed main components of the gyrotron (the diamond window, cavity resonator and quasi-optical mode converter). We found the optimum parameter set from the parameters of these components, which has discrete characteristics. It was confirmed that the output power higher than 1 MW is obtained for both frequencies as a result of numerical design. Based on the above design, a dual frequency gyrotron was newly fabricated. In the conditioning operation, an output power was obtained as we expected.

Journal Articles

Hydrogen isotopes retention in gaps at the JT-60U first wall tiles

Yoshida, Masafumi; Tanabe, Tetsuo*; Hayashi, Takao; Nakano, Tomohide; Fukumoto, Masakatsu; Yagyu, Junichi; Miyo, Yasuhiko; Masaki, Kei; Itami, Kiyoshi

Fusion Science and Technology, 63(1T), p.367 - 370, 2013/05

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

In this study, the retentions of hydrogen isotopes (H and D) in the gaps in JT-60U are clarified. Carbon tiles used in 1992-2004 were poloidally and toroidally taken out from outboard first wall in JT-60U to measure the retentions. The H and D retentions in the samples were measured by thermal desorption spectrometry (TDS). The H+D retention in the top side was higher than that of the bottom side, which might be due to thicker re-deposited carbon layers on the surface of the top side. The retentions in the surface of the side surfaces were slightly lower than that in the plasma facing surface where the retention was saturated to be 3-4e22 atoms/m$$^{2}$$. The retention rate was evaluated to be 3e17 H+D atoms/m$$^{2}$$/s from the measured retentions in two different discharge times by assuming the retention to increase linearly with the discharge time.

Journal Articles

Nuclear analysis of ITER equatorial EC launcher

Takahashi, Koji; Iida, Hiromasa*; Kobayashi, Noriyuki*; Kajiwara, Ken; Sakamoto, Keishi; Omori, Toshimichi*; Henderson, M.*

Fusion Science and Technology, 63(1T), p.156 - 159, 2013/05

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

Nuclear analysis of the ITER equatorial EC launcher has been carried out to determine heat and/or particle loads on its components and also to evaluate the possibility of "hands-on maintainability" (personnel accessibility) to the launcher back-end. Monte Carlo code "MCNP5" is applied to simulate the radiation leak from fusion plasma to the special region around the launcher. The results indicate a significant radiation leak at the gaps between the port walls and port plug frame and at the waveguide bundles in the launcher. Another significant neutron leakage is through the port wall consisting of only stainless steel but without light isotopes such as water. The shut down dose rates was estimated at the port interspace behind the launcher at the level of the required value of 100 $$mu$$Sv/h. This analysis offers the potential to modify the launchers shielding layout to minimize the above leakage and further reduce the shut down dose rates in the regions of personnel access.

Journal Articles

Design and operation of TE$$_{31,12}$$ high power gyrotron

Kajiwara, Ken; Oda, Yasuhisa; Takahashi, Koji; Kasugai, Atsushi; Sakamoto, Keishi

Fusion Science and Technology, 63(1T), p.35 - 39, 2013/05

 Times Cited Count:2 Percentile:74.98(Nuclear Science & Technology)

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