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Journal Articles

Pressure-modulated magnetism and negative thermal expansion in the Ho$$_2$$Fe$$_{17}$$ intermetallic compound

Cao, Y.*; Zhou, H.*; Khmelevskyi, S.*; Lin, K.*; Avdeev, M.*; Wang, C.-W.*; Wang, B.*; Hu, F.*; Kato, Kenichi*; Hattori, Takanori; et al.

Chemistry of Materials, 35(8), p.3249 - 3255, 2023/04

 Times Cited Count:0 Percentile:0(Chemistry, Physical)

Hydrostatic and chemical pressure are efficient stimuli to alter the crystal structure and are commonly used for tuning electronic and magnetic properties in materials science. However, chemical pressure is difficult to quantify and a clear correspondence between these two types of pressure is still lacking. Here, we study intermetallic candidates for a permanent magnet with a negative thermal expansion (NTE). Based on in situ synchrotron X-ray diffraction, negative chemical pressure is revealed in Ho$$_2$$Fe$$_{17}$$ on Al doping and quantitatively evaluated by using temperature and pressure dependence of unit cell volume. A combination of magnetization and neutron diffraction measurements also allowed one to compare the effect of chemical pressure on magnetic ordering with that of hydrostatic pressure. Intriguingly, pressure can be used to control suppression and enhancement of NTE. Electronic structure calculations indicate that pressure affected the top of the majority band with respect to the Fermi level, which has implications for the magnetic stability, which in turn plays a critical role in modulating magnetism and NTE. This work presents a good example of understanding the effect of pressure and utilizing it to control properties of functional materials.

Journal Articles

Status of the J-PARC RF-driven H$$^{-}$$ ion source

Oguri, Hidetomo; Okoshi, Kiyonori; Shinto, Katsuhiro; Shibata, Takanori*; Nammo, Kesao*; Ikegami, Kiyoshi*; Takagi, Akira*; Ueno, Akira

JPS Conference Proceedings (Internet), 33, p.011008_1 - 011008_7, 2021/03

A cesiated RF-driven negative hydrogen ion source was initiated to operate in September, 2014 in response to the need for upgrading J-PARC's linac beam current. The ion source mainly comprises a stainless-steel plasma chamber, a beam extractor and a large vacuum chamber equipped with two turbo molecular pumps, each having the pumping speed of 1500 L/s, for differential pumping. The user operation was started with the beam current of 33 mA from the ion source. We gradually increased both beam current and continuous operation time of the ion source. In July, 2018 (Run#79), approximately 2,200 hours operation was achieved with the typical beam current, pulse length and repetition rate of 47 mA, 300 $$mu$$s and 25 Hz, respectively. Since October, 2018 (Run#80), the ion source has been delivering a nominal beam current of approximately 60 mA.

Journal Articles

Operation status of the J-PARC ion source

Oguri, Hidetomo; Okoshi, Kiyonori; Ikegami, Kiyoshi*; Yamazaki, Saishun; Takagi, Akira*; Koizumi, Isao; Ueno, Akira

JPS Conference Proceedings (Internet), 8, p.011009_1 - 011009_6, 2015/09

JAEA Reports

Disassembly of the NBI system on JT-60U for JT-60 SA

Akino, Noboru; Endo, Yasuei; Hanada, Masaya; Kawai, Mikito*; Kazawa, Minoru; Kikuchi, Katsumi*; Kojima, Atsushi; Komata, Masao; Mogaki, Kazuhiko; Nemoto, Shuji; et al.

JAEA-Technology 2014-042, 73 Pages, 2015/02


According to the project plan of JT-60 Super Advanced that is implemented as an international project between Japan and Europe, the neutral beam (NB) injectors have been disassembled. The disassembly of the NB injectors started in November, 2009 and finished in January, 2012 without any serious problems as scheduled. This reports the disassembly activities of the NB injectors.

Journal Articles

Progress of neutral beam injection system on JT-60U for long pulse operation

Ikeda, Yoshitaka; NBI Heating Group; NCT Design Team

Journal of the Korean Physical Society, 49, p.S43 - S47, 2006/12

There are two type of NBI systems on JT-60U. One is the positive ion-based NBI (P-NBI) to inject the beam energy of 80-85 kV. The other is the negative ion-based NBI (N-NBI) at the beam energy more than 350 keV. Recently the pulse duration of NBI system was required to extend up to 30 sec so as to study long pulse plasmas. The four P-NBI units, which tangentially inject neutral beam to plasma, were modified to extend the pulse duration up to 30 sec with 2 MW/unit at $$sim$$ 85 keV. The seven P-NBI units, each of which perpendicularly injects for 10 sec, were conducted to operate in series for the total pulse duration of 30 sec. The ion source of the N-NBI unit was also modified to reduce the heat load of the grid for 30 sec operation. The pulse duration was extended up to 25 sec, $$sim$$ 1 MW at the beam energy of 350keV. In the next step, further pulse extension of NBI up to 100 sec is planned for the modified JT-60U with superconducting coils (so called NCT). This paper reports the recent progress of the NBI system on JT-60U and the design study of the upgraded NBI system for NCT.

Journal Articles

1 MeV, ampere class accelerator R&D for ITER

Inoue, Takashi; Kashiwagi, Mieko; Taniguchi, Masaki; Dairaku, Masayuki; Hanada, Masaya; Watanabe, Kazuhiro; Sakamoto, Keishi

Nuclear Fusion, 46(6), p.S379 - S385, 2006/06

 Times Cited Count:35 Percentile:75.18(Physics, Fluids & Plasmas)

The JAERI MeV accelerator has been designed extrapolating vacuum insulation design guidelines (the clump theory and Paschen law) to Mega Volt and long vacuum gap. Reduction of electric field concentration at triple junction by a large stress ring was effective to prevent flashover along insulator surface. By the vacuum insulation technology above, the accelerator sustained 1 MV for 8,500 s continuously. Strong enhancement of negative ion surface production has been attained by stopping vacuum leaks due to SF$$_{6}$$ permeation through Viton O rings and a damage of port by backstream ions, followed by increase of the H$$^{-}$$ ion current density without saturation. Operating the KAMABOKO source with high power arc discharge ($$leq$$ 40 kW), H$$^{-}$$ ion beams of 146 A/m$$^{2}$$ (total ion current: 0.2 A) have been obtained stably at the beam energy of 836 keV (pulse length: $$geq$$ 0.2 s). Bremsstrahlung generation in the accelerator is also estimated from EGS4 analysis, and then discussion on the breakdown possibility follows.

Journal Articles

Operation of the electrostatic accelerators

Mizuhashi, Kiyoshi; Uno, Sadanori; Okoshi, Kiyonori; Chiba, Atsuya; Yamada, Keisuke; Saito, Yuichi; Ishii, Yasuyuki; Sakai, Takuro; Sato, Takahiro; Yokota, Wataru; et al.

JAEA-Review 2005-001, TIARA Annual Report 2004, P. 371, 2006/01

no abstracts in English

Journal Articles

Positive and negative ion sources for magnetic fusion

Hemsworth, R. S.*; Inoue, Takashi

IEEE Transactions on Plasma Science, 33(6), p.1799 - 1813, 2005/12

 Times Cited Count:88 Percentile:92.51(Physics, Fluids & Plasmas)

The positive or negative ion sources which form the primary components of neutral beam injection systems used in magnetic fusion have to meet simultaneously several demanding requirements. This paper describes the underlying physics of modern positive ion sources, which provide the required high proton fraction ($$>$$90%) and high current density ($$approx$$2 kA/m$$^{2}$$) at a low source pressure (0.4 Pa) with a high electrical efficiency and uniformity across the accelerator grids. The development of negative ion sources, which are required if high energy neutral beams are to be produced, is explained. The paper reports that negative ion sources have achieved many of the parameters required of sources for the neutral beam injectors of future fusion devices and reactors, $$>$$200 A/m$$^{2}$$ of D$$^{-}$$ at low pressure, $$<$$0.3 Pa, with low co-extracted electron content. The development needed to meet all the requiremens of future systems is briefly discussed.

Journal Articles

Experimental study on spatial uniformity of H$$^{-}$$ ion beam in a large negative ion source

Hanada, Masaya; Seki, Takayoshi*; Takado, Naoyuki*; Inoue, Takashi; Morishita, Takatoshi; Mizuno, Takatoshi*; Hatayama, Akiyoshi*; Imai, Tsuyoshi*; Kashiwagi, Mieko; Sakamoto, Keishi; et al.

Fusion Engineering and Design, 74(1-4), p.311 - 317, 2005/11

 Times Cited Count:7 Percentile:45.32(Nuclear Science & Technology)

no abstracts in English

Journal Articles

N-NBI heating and current drive in JT-60U towards steady-state tokamak

Ikeda, Yoshitaka; Oikawa, Toshihiro; Ide, Shunsuke

Purazuma, Kaku Yugo Gakkai-Shi, 81(10), p.773 - 778, 2005/10

In steady-state tokamak fusion reactors, an efficient external current drive and a large fraction of the bootstrap current are required for non-inductive operation at low circulating power. NBI is a powerful and reliable actuator for current drive and heating. A negative ion-based NBI (N-NBI) with a high beam energy more than 350 keV has been installed in the JT-60U tokamak in order to study the NBI current drive and heating in an ITER relevant regime. This paper presents recent progress of N-NBI experiments and its system in JT-60U towards steady-state operation for ITER and tokamak fusion reactors.

Journal Articles

R&D on a high energy accelerator and a large negative ion source for ITER

Inoue, Takashi; Taniguchi, Masaki; Morishita, Takatoshi; Dairaku, Masayuki; Hanada, Masaya; Imai, Tsuyoshi*; Kashiwagi, Mieko; Sakamoto, Keishi; Seki, Takayoshi*; Watanabe, Kazuhiro

Nuclear Fusion, 45(8), p.790 - 795, 2005/08

The R&D of a 1 MeV accelerator and a large negative ion source have been carried out at JAERI. The paper presents following progress as a step toward ITER NB system. (1) Accelerator R&D: According to success in improvement of voltage holding capability, the acceleration test of H$$^{-}$$ ions up to 1 MeV class energy is in progress. H$$^{-}$$ ion beams of 1 MeV, 100 mA class have been generated with a substantial beam current density (100 A/m$$^{2}$$), and the current density is still increasing by the ion source tuning. (2) Large ion source R&D: One of major causes that limited the NB injection performance was spatial unifomity of negative ion production in existing negative-ion based NB systems. The present study revealed that the negative ions produced in the extraction region of the source were locally destructed by fast electrons leaking through magnetic filter. Some countermeasures and their test results are also described.

Journal Articles

R&D on a high energy accelerator and a large negative ion source for ITER

Inoue, Takashi; Taniguchi, Masaki; Morishita, Takatoshi; Dairaku, Masayuki; Hanada, Masaya; Imai, Tsuyoshi*; Kashiwagi, Mieko; Sakamoto, Keishi; Seki, Takayoshi*; Watanabe, Kazuhiro

Nuclear Fusion, 45(8), p.790 - 795, 2005/08

 Times Cited Count:23 Percentile:60.05(Physics, Fluids & Plasmas)

The R&D of a 1 MeV accelerator and a large negative ion source has been carried out at JAERI for the ITER NB system. The R&D is in progress at present toward: (1) 1 MeV acceleration of H$$^{-}$$ ion beams at the ITER relevant current density of 200 A/m$$^{2}$$, and (2) improvement of uniform negative ion production over wide extraction area in large negative ion sources. Recently, H$$^{-}$$ ion beams of 1 MeV, 140 mA level have been generated with a substantial beam current density (100 A/m$$^{2}$$). In the uniformity study, it has been clarified that electron temperature in the ion extraction region is locally high ($$>$$ 1 eV), which resulted in destruction of negative ions at a high reaction rate. Interception of fast electrons leaking through a transverse magnetic field called "magnetic filter" has been found effective to lower the local electron temperature, followed by an improvement of negative ion beam profile.

Journal Articles

Acceleration of 100 A/m$$^{2}$$ negative hydrogen ion beams in a 1 MeV vacuum insulated beam source

Taniguchi, Masaki; Inoue, Takashi; Kashiwagi, Mieko; Hanada, Masaya; Watanabe, Kazuhiro; Seki, Takayoshi*; Sakamoto, Keishi

AIP Conference Proceedings 763, p.168 - 175, 2005/04

The accelerator for the ITER NB system is required to produce 1 MeV, 40 A D-ion beams for 16.5 MW neutral beam injection per module. In the ITER NB system, conventional gas insulated beam source cannot be adopted because of the radiation-induced conductivity of the insulation gas. Thus a vacuum insulated beam source (VIBS), where the whole beam source is immersed in vacuum, had been developed in JAERI. Recently, voltage holding capability of the VIBS was drastically improved by installing the large stress ring, which reduces the electric field concentration at the negative side triple junction. Having improved the voltage holding capability of the VIBS, the H$$^{-}$$ ion beams were extracted with seeding cesium to enhance the negative ion currents. Up to now, we had been succeeded in accelerating the H$$^{-}$$ beam of 102 A/m$$^{2}$$ (140 mA) at 800 keV. The beam acceleration was quite stable and accomplished for several hundreds shots in several experimental campaigns.

JAEA Reports

R&D on high power negative ion sources and accelerators for a neutral beam injector

Inoue, Takashi

JAERI-Research 2005-006, 87 Pages, 2005/03


Negative ion sources and accelerators have been developed toward the ITER neutral beam injector (NBI). According to an analysis of negative ion surface production, the "KAMABOKO" ion source has been developed maximizing its volume/surface ratio, for fast electron confinement followed by enhancement of atomic density. An "external filter" is equipped in the source, to suppress ion destruction by the fast electrons with efficient diffusion of the atoms to ion extraction region. H$$^{-}$$ ions of 300 A/m$$^{2}$$ was extracted at the pressure of 0.3 Pa. For the accelerator, vacuum insulation technology has been developed since insulation gas such as SF$$_{6}$$ is not applicable under radiation environment. Considering pressure in the accelerator (0.02$$sim$$0.2 Pa), insulation guideline has been developed for both vacuum arc and glow discharges. Reduction of electric field stress at triple junction was effective to prevent flashover along insulator surface. H$$^{-}$$ ion beams of 900 keV and 80 A/m$$^{2}$$ (total ion current: 0.11 A) were obtained for several hundred shots.

Journal Articles

Intelligible seminor on fusion reactors, 3; Plasma heating system to generate high temperature fusion palsmas

Inoue, Takashi; Sakamoto, Keishi

Nihon Genshiryoku Gakkai-Shi, 47(2), p.120 - 127, 2005/02

no abstracts in English

Journal Articles

Characterization of interface defects related to negative-bias temperature instability in ultrathin plasma-nitrided SiON/Si$$<$$100$$>$$ systems

Fujieda, Shinji*; Miura, Yoshinao*; Saito, Motofumi*; Teraoka, Yuden; Yoshigoe, Akitaka

Microelectronics Reliability, 45(1), p.57 - 64, 2005/01

 Times Cited Count:11 Percentile:51.65(Engineering, Electrical & Electronic)

To characterize the interface defects that are responsible for the negative-bias temperature instability (NBTI) of a thin plasma-nitrided SiON/Si system, we carried out inerface trap density measurements, electron-spin resonance spectroscopy and synchrotron radiation XPS. The NBTI was shown to occur mainly through the dehydrogenation of the interfacial Si dangling bonds (P$$_{b}$$ defects). Although we suggest that non- P$$_{b}$$ defects are also generated by the negative-bias temperature stress, nitrogen dangling bonds do not seem to be included. The plasma-nitridation process was confirmed to generate sub-oxides at the interface and thus increase the interface trap density. Furthermore, it was found that the nitridation induces another type of P$$_{b1}$$ defect than that at pure-SiO$$_{2}$$/Si interfacec. Such an increase and structural change of the interfacial defects are likely the causes of the nitridation-enhanced NBTI.

Journal Articles

Actively-cooled plasma electrode for long pulse operations in a cesium-seeded negative ion source

Fujiwara, Yukio; Watanabe, Kazuhiro; Okumura, Yoshikazu; Trainham, R.*; Jacquot, C.*

Review of Scientific Instruments, 76(1), p.013501_1 - 013501_5, 2005/01

 Times Cited Count:0 Percentile:0.01(Instruments & Instrumentation)

A new actively-cooled plasma electrode has been developed for long pulse operation in a cesium-seeded negative ion source. To keep the electrode temperature at about 300 $$^{circ}$$C, which is optimum range of temperature to enhance cesium effects, the electrode cooling structure has been designed using three-dimensional numerical simulation assuming that the heat flux from the source plasma was 15 W/cm$$^{2}$$. Water cooling tubes were brazed to the plasma electrode substrate with spacers made of stainless steel which acts as a thermal resistance. The fabricated plasma electrode has been tested in a cesium-seeded volume negative ion source called Kamaboko source. The temperature of the electrode reached 280 $$^{circ}$$C for the arc power of 41 kW, which is operating condition required for producing D- beams with current densities exceeding 20 mA/cm$$^{2}$$. It was demonstrated that the actively-cooled plasma electrode is applicable to long pulse operations, meeting the temperature requirement for optimizing the surface-production process of negative ions in the cesium seeded ion source.

Journal Articles

Leak-tightness characteristics concerning the containment structures of the HTTR

Sakaba, Nariaki; Iigaki, Kazuhiko; Kondo, Masaaki; Emori, Koichi

Nuclear Engineering and Design, 233(1-3), p.135 - 145, 2004/10

 Times Cited Count:5 Percentile:35.66(Nuclear Science & Technology)

The containment structures of the HTTR consist of the reactor containment vessel, the service area, and the emergency air purification system, which minimise the release of fission products in postulated accidents which lead to fission product release from the reactor facilities. The reactor containment vessel is designed to withstand the temperature and pressure transients and to be leak-tight in the case of a rupture of the primary concentric hot gas duct, etc. The pressure inside the service area is maintained at a negative pressure by the emergency air purification system. The emergency air purification system will also remove airborne radio-activity and will maintain a correct pressure in the service area. The leak-tightness characteristics of the containment structures are described in this paper. The measured leakage rates of the reactor containment vessel were enough less than the specified leakage limit of 0.1%/d confirmed during the commissioning tests and annual inspections. The service area was kept the design pressure well below its allowable limitation by the emergency air purification system which filter efficiency of particle removal and iodine removal were well over the limited values. The obtained data demonstrates that the reactor containment structures were fabricated to minimise the release of fission products in the postulated accidents with fission product release from the reactor facilities.

Journal Articles

Acceleration of 1 MeV, 100 mA class H$$^{-}$$ ion beams in a proof-of-principle accelerator for ITER

Inoue, Takashi; Taniguchi, Masaki; Dairaku, Masayuki; Hanada, Masaya; Kashiwagi, Mieko; Morishita, Takatoshi; Watanabe, Kazuhiro; Imai, Tsuyoshi

Review of Scientific Instruments, 75(5), p.1819 - 1821, 2004/05

 Times Cited Count:11 Percentile:51.73(Instruments & Instrumentation)

The paper reports progress of proof-of-principle test of negative ion accelerator for ITER. The accelerator structure is immersed in vacuum, surrounded by a FRP insulator column as the vacuum boundary. So far, the beam energy has been limited due to poor voltage holding capability of the FRP insulator column. By lowering the electric field strength at the triple junction (interface of FRP insulator, metal flange and vacuum) with large stress ring installed inside the insulator column, high voltage of 1 MV was stably sustained for more than 2 hours. In the following beam test, acceleration of 900 keV, 100 mA H$$^{-}$$ ion beam was succeeded. Although the current was lower (70 mA) at 1 MeV, the beam of this level has been stably accelerated for 6 days, 130 shots in total (each pulse length: 1 s).

Journal Articles

High proton ratio plasma production in a small negative ion source

Morishita, Takatoshi; Inoue, Takashi; Iga, Takashi*; Watanabe, Kazuhiro; Imai, Tsuyoshi

Review of Scientific Instruments, 75(5), p.1764 - 1766, 2004/05

 Times Cited Count:7 Percentile:39.85(Instruments & Instrumentation)

Negative ion beams of high current density are required for accelerator and fusion. The H$$^{-}$$ source utilizes surface production that produces H$$^{-}$$ from H or H$$^{+}$$. And hence, high proto yield ion source is required. Generally, a large volume plasma generator with strong plasma confinement is suitable to achieve high proton yield. On the contrary, production of high proton ratio plasma is not easy in small sources. However, in a small source (3.5 liter), high current H$$^{-}$$ beam of 800 A/m$$^{2}$$ was obtained. In this research, the proton ratio was investigated experimentally and analytically in a small source (1.4 liter). The measured proton ratio increased form 40% to 90% by applying the magnetic filter. From the numerical analysis, the proton ratio is low as 40% in the driver region. However, with the magnetic filter, flow of primary electrons is restrained, resulting in suppression of H$$_2^{+}$$ production at the extraction region. In addition, molecular ions are easily destroyed by thermal electrons in the filter region. Thus the proton ratio is enhanced by the magnetic field in the small sources.

122 (Records 1-20 displayed on this page)