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Journal Articles

Thermal properties of redeposition layers in the JT-60U divertor region

Ishimoto, Yuki; Goto, Yoshitaka*; Arai, Takashi; Masaki, Kei; Miya, Naoyuki; Oyama, Naoyuki; Asakura, Nobuyuki

Journal of Nuclear Materials, 350(3), p.301 - 309, 2006/05

 Times Cited Count:21 Percentile:81.69(Materials Science, Multidisciplinary)

Thermal properties of the redeposition layer on the inner plate of the W-shaped divertor of JT-60U have been measured with laser flash method for the first time so as to estimate transient heat loads onto the divertor. Measurement of a redeposition layer sample of more than 200 m thick showed following results: (1) the bulk density of the redeposition layer is about half of that of carbon fiber composite material; (2) the specific heat of the layer is roughly equal to that of the isotropic graphite; (3) the thermal conductivity of the redeposition layer is two orders of magnitude smaller than that of the carbon fiber composite. The difference between the divertor heat loads and the loss of the plasma stored energy becomes smaller taking account of thermal properties of the redeposition layer on the inner divertor, whereas estimated heat loads due to the ELMs is still larger than the loss. This is probably caused by the poloidal distribution of the thermal properties and heat flux asymmetry inherent in the device.

Journal Articles

Reduced divertor heat loads, plasma shape effects, and radial electric field structures in JFT-2M HRS H-mode plasmas

Kamiya, Kensaku; Kawashima, Hisato; Ido, Takeshi*; Oyama, Naoyuki; Bakhtiari, M.*; Kasai, Satoshi; Kusama, Yoshinori; Miura, Yukitoshi; Ogawa, Hiroaki; Tsuzuki, Kazuhiro; et al.

Nuclear Fusion, 46(2), p.272 - 276, 2006/02

 Times Cited Count:3 Percentile:11.37(Physics, Fluids & Plasmas)

An attractive operational regime without any large ELMs, namely High Recycling Steady (HRS) H-mode, was found on JFT-2M during Y2000 campaign after boronization. Recent experiments have concentrated on the studies of the access conditions for the HRS regime, in terms of the pedestal parameters. The HRS regime was more likely at higher edge density and lower edge temperature, which corresponds to the normalized electron collisionality of 1 in the plasma edge region.

Journal Articles

Pedestal characteristics in JFT-2M HRS H-mode plasma

Kamiya, Kensaku; Oyama, Naoyuki; Miura, Yukitoshi; Hubbard, A. E.*

Plasma Physics and Controlled Fusion, 46(11), p.1745 - 1755, 2004/11

 Times Cited Count:13 Percentile:41.89(Physics, Fluids & Plasmas)

Recent experiments in the JFT-2M tokamak have concentrated on the studies of the access condition for the H-mode operation without any large ELMs, namely High Recycling Steady (HRS) H-mode regime in terms of the pedestal parameters. The HRS regime is more likely at the higher edge density and lower edge temperature, while the ELMy H-mode having large ELMs appears at the lower edge density and higher edge temperature. It is found that the ELMy/HRS operational boundary occurs at the normalized electron collisionality of $$nu$$*$$_{e}$$$$sim$$1 in the plasma edge region, depending slightly on q$$_{95}$$. A key feature of the HRS H-mode is the presence of the coherent magnetic fluctuations in the frequency range of the order of 10-100 kHz. It is suggested that the edge MHD activities may keep an edge pressure below a certain level needed to induce a large ELM.

Journal Articles

High recycling steady H-mode regime in the JFT-2M Tokamak

Kamiya, Kensaku; Bakhtiari, M.; Kasai, Satoshi; Kawashima, Hisato; Kusama, Yoshinori; Miura, Yukitoshi; Ogawa, Hiroaki; Oyama, Naoyuki; Sato, Masayasu; Shinohara, Koji; et al.

Plasma Physics and Controlled Fusion, 46(5A), p.A157 - A163, 2004/05

 Times Cited Count:21 Percentile:58.52(Physics, Fluids & Plasmas)

A new operating regime, High Recycling Steady (HRS) H-mode regime, has been discovered on JFT-2M, which is easily reproduced under the wall fueling from the boronized first wall. Accompanying the HRS H-mode transition, the coherent magnetic and floating potential fluctuations are seen on magnetic probes at vessel wall and Langmuir probe in SOL, respectively. These coherent fluctuations have a frequency of the order of 10-100 kHz with significant variation, which is recognized to be important to enhance the particle transport. The HRS can be seen even at ${it q}$$$_{95}$$$$<$$3 with ${it n}$$$_{e}$$/${it n}$$$_{GW}$$$$>$$0.4 for the fixed delta$$sim$$0.4 in the standard single-null divertor configuration. Recent experimental results from JFT-2M show that the plasma shape also seems to play an important role in determining the type of ELMs. The HRS regime can be extended up to delta$$sim$$0.75 and ${it q}$$$_{95}$$$$sim$$2.6 in the double-null configuration, while lower delta boundary exists at delta$$sim$$0.3 with moderate ${it q}$$$_{95}$$$$sim$$4 even at high recycling and/or density condition of ${it n}$$$_{e}$$/${it n}$$$_{GW}$$$$>$$0.4.

Journal Articles

Observation of high recycling steady H-mode edge and compatibility with improved core confinement mode on JFT-2M

Kamiya, Kensaku; Kimura, Haruyuki; Ogawa, Hiroaki; Kawashima, Hisato; Tsuzuki, Kazuhiro; Sato, Masayasu; Miura, Yukitoshi; JFT-2M Group

Nuclear Fusion, 43(10), p.1214 - 1219, 2003/10

no abstracts in English

Journal Articles

Observation of high recycling steady H-mode edge and compatibility with improved core confinement mode on JFT-2M

Kamiya, Kensaku; Kimura, Haruyuki; Ogawa, Hiroaki; Kawashima, Hisato; Tsuzuki, Kazuhiro; Sato, Masayasu; Miura, Yukitoshi; JFT-2M Group

Nuclear Fusion, 43(10), p.1214 - 1219, 2003/10

 Times Cited Count:35 Percentile:72.54(Physics, Fluids & Plasmas)

no abstracts in English

Journal Articles

Pellet injection as a possible tool for plasma performance improvement

Polevoi, A. R.*; Sugihara, Masayoshi; Takenaga, Hidenobu; Isayama, Akihiko; Oyama, Naoyuki; Loarte, A.*; Saibene, G.*; Pereverzev, G. V.*

Nuclear Fusion, 43(10), p.1072 - 1076, 2003/10

 Times Cited Count:34 Percentile:71.79(Physics, Fluids & Plasmas)

ITER operational scenarios with the high field side pellet fuelling are considered. The possibility of reducing the energy losses per edge localised mode (ELM) to an acceptable level is discussed. Requirements on the pellet fuelling system for desirable ELM energy reduction are obtained. Self-consistent transport simulations of pellet fuelled scenarios reveal the possibility of the operation with moderate ELM losses, plasma density below Greenwald density, high energy multiplication factor Q$$sim$$20 and power across the separatrix above the L-H mode power threshold.

Journal Articles

Impurity behavior during the H-mode in JFT-2M

Ogawa, Hiroaki; Kasai, Satoshi; Tamai, Hiroshi; Kawashima, Hisato; *; Yamauchi, Toshihiko; Mori, Masahiro; Miura, Yukitoshi; Suzuki, Norio; Sengoku, Seio; et al.

Journal of the Physical Society of Japan, 59(11), p.3962 - 3976, 1990/11

 Times Cited Count:4 Percentile:46.63(Physics, Multidisciplinary)

no abstracts in English

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