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A. Kojima,
M. Hanada,
Y. Tanaka, M. Kawai,
N. Akino,
M. Kazawa,
M. Komata,
K. Mogaki,
K. Usui,
S. Sasaki, [......],
K. Oasa,
T. Inoue,
K. Watanabe,
M. Taniguchi,
M. Kashiwagi,
H. Tobari,
N. Umeda,
S. Kobayashi,
Y. Yamano,
L.R. Grisham
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ABSTRACT: Hydrogen negative ion beams of 507 keV, 1 A and 486 keV, 2.8 A have been successfully produced in the JT-60U negative ion source with a three-stage accelerator by overcoming a poor voltage holding of the accelerator with large-size grids of ~2 m2. This is the first result of H− beam acceleration up to 500 keV at a high current of over 1 A. In order to improve the voltage holding capability, the breakdown voltages of the large-size grids and small-size electrodes with uniform and locally strong electric fields were examined by changing the gap length. It was found that the voltage holding of the large-size grids was below half of that of the small-size electrodes with a uniform electric field which was used in the design of the accelerator. This degradation was found to be caused by the local electric field concentrations in addition to the size. Based on the results of the voltage holding tests and beam optics calculations, the gap lengths of the large-size grids were tuned to have a capability to sustain 600 kV. As a result, the gap tuning realized stable voltage holding during beam accelerations without significant degradations of the beam optics and stripping loss. These results indicated that stable 500 keV beam accelerations required for JT-60SA are feasible and this gap tuning is also applicable for the design of ITER accelerator.
Nuclear Fusion 08/2011; 51(8):083049. · 4.09 Impact Factor
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ABSTRACT: This paper proposes a novel structure of microelectromechanical-systems-based 1-D spatial light phase modulator (SLPM) that consists of a micromirror array on a silicon-on-insulator (SOI) wafer and indium tin oxide (ITO) electrodes on a glass plate. Each micromirror can exhibit bidirectional single-axis tilt, as well as up-and-down piston motions by combining the applied voltage on two ITO electrodes placed over the micromirror and the substrate of SOI (in the case that the substrate is energized, all micromirrors go down simultaneously). This device configuration enables SLPM to be fabricated by a simple process. Part I of this paper focuses on the principles and the design of the device. The optimum parameters of the device are derived to realize both tilt and piston motions, considering ways to reduce mirror warpage and crosstalk from the ITO electrode from the adjacent mirror. We simulate the dc and ac characteristics of the device and confirm that the designs that we optimized satisfy the target specifications to be widely used in optical communication systems.
Journal of Microelectromechanical Systems 03/2011; · 2.10 Impact Factor
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ABSTRACT: In part I of this paper, we have proposed a novel structure of microelectromechanical-systems-based 1-D spatial light phase modulator (SLPM). We have discussed the design of the device and derived the optimum parameters to satisfy the target specifications. In part II, we focus on the fabrication process and experimental results of the device. We show that this device configuration allows us to use a simple fabrication process. We fabricated the device consisted of 24 micromirrors and realized the tilt and piston motions successfully. The measured dc (rotation angle and displacement on driving voltage) and ac (frequency response) characteristics matched well to the simulated data derived in part I. We also examined the distribution of the resonant frequencies over 24 micromirrors and verified that the variance was kept within 2%. As one of the applications of the device, we applied the device to optical beam shaping and succeeded in shaping the optical beam properly depending on the surface patterns of the SLPM. With these achievements, we show that the device can be adopted to a wide variety of applications in optical communication systems and optical signal processing.
Journal of Microelectromechanical Systems 03/2011; · 2.10 Impact Factor
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N. Akino,
K Usui,
Y Endo,
K. Oasa,
K Oshima,
M. Kazawa, M Kawai,
K Kikuchi,
A Kojima,
M. Komata,
S Sasaki,
T. Simizu,
N Seki,
S Nemoto,
Y Tanaka,
K. Noto,
M Hanada,
K. Mogaki
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ABSTRACT: This addendum applies to two papers authored by contributors from the JT-60 NBI Group published in Proceedings of the 13th International Conference on Ion Sources, Gatlinburg, Tennessee, September 2009. This addendum provides the full list of JT-60 NBI Group and their affiliations.
The Review of scientific instruments 02/2010; 81(2):02F701. · 1.52 Impact Factor
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ABSTRACT: Handoff is one of the essential elements that can affect the quality of service (QoS) and capacity of mobile broadband networks. The implementation of hard handoff is obligatory for Mobile Wimax, the IEEE 802.16e standard. However, seamless mobility in mobile Wimax without interruption of real time services under hard handoff still needs more exploration. This paper proposes an adaptive mobility handoff scheme (AMHO) to improve the effect of user mobility on handoff performance in mobile Wimax networks. The key notation is to detect handoff trigger point by using mobile station's movement patterns and to modify MAC layer exchange messages in handoff process. Simulation results show that the handoff performance is effectively improved in terms of packet drop and handoff latency.
Wireless Communication, Vehicular Technology, Information Theory and Aerospace & Electronic Systems Technology, 2009. Wireless VITAE 2009. 1st International Conference on; 06/2009
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ABSTRACT: Localization of Wireless Sensor Networks (WSNs) is an issue for location-based services. This paper proposes a new Wireless Sensor Network Localization Scheme based on Self-Organizing Maps (SOM) to deal with this issue. Our scheme utilizes only connectivity information and information from some heard anchors in the network to determine the location of nodes. With anisotropic topologies or topologies having obstacles, localization schemes tend to get higher error. Our scheme not only solves well the isotropic networks, but also minimizes the error in anisotropic networks and networks having obstacles by filtering the information from heard anchors. From our intensive simulations, the results show that the proposed scheme achieves very good accuracy in most cases.
Intelligent Sensors, Sensor Networks and Information Processing, 2008. ISSNIP 2008. International Conference on; 01/2009
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Y. Ikeda,
M. Hanada,
M. Kamada,
K. Kobayashi,
N. Umeda,
N. Akino,
N. Ebisawa,
T. Inoue,
A. Honda, M. Kawai, [......],
S. Sasaki,
T. Simizu,
T. Takenouchi,
Y. Tanai,
K. Usui,
K. Watanabe,
L.R. Grisham,
S. Kobayashi,
Y. Yamano,
M. Takahashi
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ABSTRACT: The JT-60 Super Advanced (JT-60SA) tokamak aims to perform the ITER support and to demonstrate steady-state high-beta plasma project with the collaboration between Japan and EU. To attain these objectives, the negative-ion-based NBI (N-NBI) system is required to inject 10 MW for 100 s at the beam energy of 500 keV. On JT-60U, the present N-NBI ion source has injected 3.2 MW for 21 s at 320 keV; however, three key issues should be solved for the JT-60SA N-NBI ion source. One is to improve the voltage holding capability of the large negative ion source, where the available acceleration voltage has been limited to less than ~400 kV due to breakdowns. The accelerator of the JT-60U ion source is composed of large three-stage grids and three fiberglass reinforced plastic (FRP) insulators. Recent R&D tests suggested that the FRP insulators were not the main factor to trigger the breakdowns at the early conditioning stage. The accelerator with a large area of grids and their supporting structure may need a high margin in the design of electric field and a long time for conditioning. The second issue is to reduce the power loading of the acceleration grids. It was found that some beamlets were strongly deflected due to beamlet-beamlet interaction and strike on the grounded grid in the accelerator. Moreover, the electrons generated in the accelerator caused the grid loading and the overheating of the beamline components. The acceleration grids for JT-60SA are to be designed by taking account of the beamlet-beamlet interaction and the applied magnetic field in 3-D simulation. Third is to maintain the D production for 100 s. Although a constant D<sup>-</sup> beam power was confirmed on JT-60U for 21 s, an active cooling system is required to keep the temperature of the plasma grid (PG) under optimum condition during 100-s operation. A simple cooling structure is proposed for the active cooled PG, where a key is the temperature gradient on the PG for uniform D<sup>-</sup> p-
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roduction. In the present schedule, design work, reflecting the latest R&D progress, will continue until ~2011. The modified N-NBI ion source will start on JT-60SA in 2015.
IEEE Transactions on Plasma Science 09/2008; · 1.17 Impact Factor
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M Hanada,
M Kamada,
N Akino,
N Ebisawa,
A Honda, M Kawai,
M Kazawa,
K Kikuchi,
M Komata,
K Mogaki,
K Noto,
K Ohshima,
T Takenouchi,
Y Tanai,
K Usui,
H Yamazaki,
Y Ikeda,
L R Grisham
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ABSTRACT: The first long pulse production of high power D(-) ion beams has been demonstrated in the JT-60 U negative ion sources, each of which was designed to produce 22 A, 500 keV D(-) ion beams. Voltage holding capability and the grid power loading were examined for long pulse production of high power D(-) ion beams. From the correlation between voltage holding and the light intensity of cathodoluminescence from the Fiber Reinforced Plastic insulators, the acceleration voltage for stable voltage holding capability was found to be less than 320-340 kV where the light was sufficiently suppressed. By tuning the extraction voltage, the grid power loadings in the ion sources were decreased to the allowable levels for long pulse injection without a significant reduction of the beam power. After tuning the acceleration and extraction voltages, D(-) ion beams of 12.5 and 9.8 A were produced at 340 keV with cesium seeding at a rate of approximately 14 microg/s into the ion sources. The pulse duration of these D(-) ion beams was extended step by step, and then was successfully extended up to 18 s without degradation of the negative ion production. The D(-) ion beams were neutralized to yield 3.6 MW D(0) beams by a gas cell, and then injected into the JT-60 U plasma. Further, a slight reduction of D(-) ion beam power allowed the longer injection duration of 21 s at a D(0) beam power of 3.2 MW. The success in the long pulse production of a high power D(-) ion beam shows that negative ion beams can be produced during a few tens of seconds without degradations of negative ion production and the voltage holding in a large Cs-seeded negative ion source.
Review of Scientific Instruments 03/2008; 79(2 Pt 2):02A519. · 1.37 Impact Factor
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ABSTRACT: In these days, an endoscope is applied to therapy as well as a diagnosis. Especially, the early gastric cancer can be treated by either endoscopic mucosa resection (EMR) or endoscopic submucosal dissection (ESD). So, pathological information of the depth direction of mucosal tissue is very important. For a precise endoscopic diagnosis of a depth direction of mucosal tissue is used by ultrasound endoscope. And optical coherence tomography (OCT) and confocal endoscope will be used in the future. Though these methods are very complicate and have many problems to have to be solved. If it becomes using clinically both the current endoscope and such new endoscope in the future, the patients probably may be suffered twice. And the development of image sensors is fast enough to make new endoscopic diagnosis. So we studied potentiality of three dimension measurement of gastrointestinal tract surface and mucosa internal structure with the present endoscope. Because the three-dimensional measurement procedure of the gastrointestinal surface that we adopted was manual, it was not suitable for a serial three-dimensional measurement. Therefore we performed a three-dimensional measurement by image processing by a motion image.
Innovative Computing, Information and Control, 2007. ICICIC '07. Second International Conference on; 10/2007
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ABSTRACT: One problem with multicarrier CDMA systems is that they often produce large values of peak to average power ratio (PAPR). Here, the correlation properties of the user spreading codes are closely related to PAPR and hence suitable allocation of spreading codes can result in reduced PAPR. In this context, we analyze the PAPR characteristics of a very recently proposed orthogonal set of codes called "Orthogonal binary user codes" and compare them with the well known Walsh-Hadamard codes. In particular, we construct and present a user spreading code allocation table through suitable selection of code subsets from the orthogonal binary user codes that perform better than corresponding Walsh-Hadamard codes.
Personal, Indoor and Mobile Radio Communications, 2007. PIMRC 2007. IEEE 18th International Symposium on; 10/2007
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E. Nakamura,
T. Adachi,
Y. Arakida,
T. Dixit,
S. Inagaki,
T. Iwashita, M. Kawai,
T. Kikuchi,
T. Kono,
K. Okazaki,
H. Sato,
Y. Shimosaki,
K. Takayama,
K. Torikai,
M. Wake
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ABSTRACT: A medium-energy synchrotron capable of accelerating all ion species based on a novel technology of the induction synchrotron has been proposed as an all-ion accelerator (AIA). The AIA without any specific injector employs a strong focusing lattice for ion-beam guiding and induction acceleration cells for acceleration and longitudinal capture, which are driven by a novel switching power supply. All ions, including cluster ions in their possible and arbitrary charge state, are accelerated in a single accelerator. A plan to modify the existing KEK 500 MeV Booster synchrotron to the AIA is under consideration. Important aspects in a 200 kV ion source, and specific features in the orbit correction associated with the low-field injection and induction acceleration, are described.
Particle Accelerator Conference, 2007. PAC. IEEE; 07/2007
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ABSTRACT: We have proposed a novel structure of one dimensional spatial light phase modulator (SLPM) that consists of a micromirror array on an SOI wafer and ITO (Indium Tin Oxide) electrodes on a glass plate. Each micromirror can exhibit bidirectional single-axis rotation, as well as up- and down- translation motion. We have fabricated the device, and confirmed its motion experimentally.
Solid-State Sensors, Actuators and Microsystems Conference, 2007. TRANSDUCERS 2007. International; 07/2007
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ABSTRACT: We demonstrated 10 Gbps of transmission in 300 m of multimode fiber using a temperature independent quantum dot laser with a directly modulated constant driving current. Error-free transmission and clear eye opening was maintained up to 80degC with an optical receiver using an electric dispersion compensator
Optical Fiber Communication Conference, 2006 and the 2006 National Fiber Optic Engineers Conference. OFC 2006; 04/2006
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ABSTRACT: In the JT-60U negative-ion-based neutral beam injection system, the effect of negative ion and electron deflection by the plasma grid (PG) magnetic filter was studied. After a long-pulse operation of up to 19 s, a local melting was observed on the beamline near the ion source, facing the electron drift side of the PG magnetic field. It is confirmed that the experimental deflection of the negative-ion beam agrees well with the three-dimensional beam simulation result by taking account of the measured magnetic field. By using the code, it is found that some stripped electrons produced in the first acceleration gap pass through the down pitch of the multiple apertures in the next stage of acceleration grids, and then collide on the beamline around the melted location.
Review of Scientific Instruments 03/2006; 77(3):03A529-03A529-3. · 1.37 Impact Factor
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ABSTRACT: This paper describes the motor constant of a cylindrical moving magnet-type linear actuator for obtaining high response characteristics. The theoretical expression of motor constant square density G is deduced using the permeance method. A prototype linear actuator is designed in both permeance method and the finite element method. Measured motor constant and motor constant square density of the prototype linear actuator are 17.1 N<sup>2</sup>/(Wm<sup>3</sup>) and 2.6×10<sup>6</sup>N<sup>2</sup>/(Wm<sup>3</sup>) respectively, where these values are over twice as large as those of conventional linear motors.
IEEE Transactions on Magnetics 11/2005; · 1.36 Impact Factor
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N. Ebisawa,
N. Akino,
L. Grisham,
M. Hanada,
A. Honda,
T. Inoue, M. Kawai,
M. Kazawa,
K. Kikuchi,
M. Komata, [......],
F. Okano,
T. Ohga,
K. Oshima,
T. Takenouchi,
Y. Tanai,
N. Umeda,
K. Usui,
H. Yamazaki,
T. Yamamoto,
Y. Ikeda
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ABSTRACT: The pulse duration of the negative ion based NBI system has been extended from 10 s to 25 s to study long pulse plasmas on JT-60U. A feedback control technique has been demonstrated to keep the arc power constant by controlling the filament voltage for long pulse operation. Thus it was clearly observed that the negative ion beam current increased with the temperature of the plasma grid at constant arc power. A tapered filament is employed to improve its durability for the next operational campaign. Moreover, a high voltage holding test indicates that the reduction in the outgassing from the FRP (fiberglass-reinforced plastic) insulator may be a key to suppress the breakdowns in the ion source
Fusion Engineering 2005, Twenty-First IEEE/NPS Symposium on; 10/2005
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ABSTRACT: An electron pulse stretcher ring (STB ring) [1] at Laboratory of Nuclear Science (LNS) in Tohoku University provides quasi-cw electron beam for the study of nuclear physics. The extracted beam from the ring has certain spread in time and space resulted from the emittance of injected beam from linac even if the injected beam is perfectly matched to the ring optics. However, the extracted beam emittance can be reduced by applying a phase space manipulation. Under the effect of perturbation using an RF shaker driven by a mono-frequency, the betatron amplitude of circulating beam can be controlled in order to reduce the extracted beam emittance. We have demonstrated the reduction of emittance experimentally on the STB ring.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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ABSTRACT: Recently sub-picosecond electron pulses are paid attention because of valious applications of THz coherent radiation emitted from such short bunches. Although photoinjetcors using RF guns are rapidly developped as high blliiant electron sources, while thermionic RF guns are still expected to have potential ability to create high-brightness and short-pulse beams [1]. In particular, components of a thermionic RF gun are simple, compact and low-cost than those of a photo-cathode RF gun. For creating such beams, a prototype of thermionic RF gun was designed and its characteristics have been studied by a 3-D simulation code based on an FDTD (Finite Difference Time Demain) method which has been developed so far [2]. The gun is consists of two independently power feeding S-band RF cavities. The first cell is a cathode cell to extract the beam and the second one is an accelerating cell. This gun can be operated at modes with different RF-power ratio and phase between two RFs. A similar way of operating RF gun has been already reported by Lewellen [3]. This paper describes the results of simulations for this thermionic RF gun.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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F. Hinode,
H. Hama, M. Kawai,
A. Kurihara,
M. Mutoh,
M. Nanao,
Y. Shibasaki,
S. Takahashi,
T. Tanaka,
A. Miyamoto,
K. Shinto
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ABSTRACT: A 1.2 GeV Stretcher-Booster Ring (STB ring) has been routinely operated at Laboratory of Nuclear Science (LNS), Tohoku University. The STB ring has functions of a pulse-beam stretcher and a booster-storage ring [1, 2]. In the booster-storage operation, high energy gamma-ray beam generated via bremsstrahlung from internal target wire is utilized for experiments of nuclear physics. Some fractions of circulating electrons are also deflected in the target wire due to Coulomb scattering without significant loss of the energy. The scattered electrons that are not getting out of the dynamic aperture once can circulate in the ring. Such electrons, however, would hit the chamber walls and supports of the target wire during further turns, because they have very large betatron amplitude. Consequently the Coulomb scattered electrons must be a source of significant background and may cause a degradation of gamma-ray beam quality. The quality of the gamma-ray beam has been improved by modifying the lattice functions of the ring. We present the details of the modification and the result of the improvement.
Particle Accelerator Conference, 2005. PAC 2005. Proceedings of the; 06/2005
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M. Kawai,
N. Akino,
N. Ebisawa,
L. Grisham,
M. Hanada,
A. Honda,
T. Inoue,
M. Kazawa,
K. Kikuchi,
M. Kuriyama, [......],
K. Mogaki,
K. Noto,
T. Ohga,
K. Ooshima,
Y. Tanai,
N. Umeda,
K. Usui,
T. Yamamoto,
H. Yamazaki,
K. Watanabe
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ABSTRACT: The negative-ion based neutral beam injection system developed by JAERI for JT-60U has been intended to generate a 500 keV and 10 MW beam for 10 seconds with two ion sources. Technical efforts to decrease heat loads on the accelerator grids, to improve non-uniformity of the source plasma, to increase voltage holding of the accelerator, and to optimize the operational parameters have been conducted intensively. A step-down control of the filament voltage was very effective to keep the acceleration current constant during the pulse duration. To suppress degradation of voltage holding of the accelerator, protection spark gaps of {approx}178 kV for each stage, its gap length is 73 mm, were confirmed to be effective.As results of these improvements, as of June 2002, the maximum injection power has reached 6.2 MW, and a pulse length has attained 10 seconds of the design value with a 2.6 MW beam.
Fusion Science and Technology 09/2003; 44(2). · 1.12 Impact Factor
