Publications (77)71.91 Total impact
-
Article: Laser-shock compression and Hugoniot measurements of liquid hydrogen to 55 GPa
[show abstract] [hide abstract]
ABSTRACT: The principal Hugoniot for liquid hydrogen was obtained up to 55 GPa under laser-driven shock loading. The pressure and density of compressed hydrogen were determined by impedance matching to a quartz standard. The shock temperature was independently measured from the brightness of the shock front. Hugoniot data of hydrogen provide a good benchmark to modern theories of condensed matter. The initial number density of liquid hydrogen is lower than that for liquid deuterium, and this results in shock-compressed hydrogen having a higher compression and higher temperature than deuterium at the same shock pressure.Phys. Rev. B. 01/2011; 83(5). -
Article: Hugoniot and temperature measurements of liquid hydrogen by laser-shock compression
[show abstract] [hide abstract]
ABSTRACT: Hydrogen at high pressure in the fluid state is of great interest for target design of inertial confinement fusion and understanding the interior structure of gas giant planets. In this work, we successfully obtained the Hugoniot data for liquid hydrogen up to 55 GPa under laser-driven shock loading using impedance matching to a quartz standard. The shocked temperature was determined simultaneously by the brightness temperature. The compression and temperature along the principal Hugoniot are in good agreement with theoretical models. High reflectivity of hydrogen was observed at 40 GPa, which suggests the fluid becomes conducting.Journal of Physics Conference Series 09/2010; 244(4):042018. -
Article: Laser machining for fabrication of targets used in the FIREX-I project
[show abstract] [hide abstract]
ABSTRACT: This paper reports on way to fabricate a gas-tight targets dedicated for the first stage of Fast Ignition Realization Experiment (FIREX-I) at the Institute of Laser Engineering (ILE), Osaka University. It was found that a Ti;sapphire laser machining can be used to fabricate the target. The performance of the laser machining using a fs Ti;sapphire laser was examined on shell materials. The conditions for accurate machining were determined. Michelson interferometer with two different wavelengths which imitates a white light interferometer is an excellent tool for confirming the gas-tightness of the target after assembly.Journal of Physics Conference Series 09/2010; 244(3):032038. -
Article: Study on possible fuel layering sequence for FIREX target
[show abstract] [hide abstract]
ABSTRACT: A new procedure of fuel layering for the Fast Ignition Realization Experiment (FIREX) target is proposed. A conical laser guide heating technique was experimentally demonstrated in principle as the followings. It employed the target consisting of a polystyrene (PS) shell, a fill tube and a conical laser guide. At first, liquid fuel was fed into the shell and existed around the conical laser guide because the surface tension of the fuel must cause it. Then, it was solidified. The laser light provided a heat source to the conical laser guide so that the solid fuel was moved to the other interior of the shell. This process resulted in missing solid fuel around the conical laser guide. To fill the vacant space, liquid fuel was added as temperature was raised to the melting point. After the liquid fuel addition, temperature was lowered to the solidification point again. During this process, most of the solid fuel could survive.Journal of Physics Conference Series 09/2010; 244(3):032039. -
Article: Present status and future prospect of Fast Ignition Realization Experiment (FIREX) Project at ILE, Osaka
[show abstract] [hide abstract]
ABSTRACT: Thermonuclear ignition and subsequent burn are key physics for achieving laser fusion. In fast ignition, a highly compressed fusion fuel generated with multiple ns‐laser beams is rapidly heated with a large energy, ps‐laser pulse in prior to core disassembly. This scheme has a high potential to achieve ignition and burn since driver energy required for high fusion gain is predicted to be about one tenth of that needed for the central ignition scheme. In Japan, Fast Ignition Realization Experiment (FIREX) project has been started to clarify the physics of energy transport and deposition in the core plasma and to demonstrate fuel temperature of above 5 keV. After the success, FIREX‐I will be followed by the second phase of the project (FIREX‐II) to demonstrate ignition and burn. LFEX laser, designed to deliver a laser pulse of 10 kJ in 10 ps, are operational and the first phase of FIREX experiments has been stated. A new target is proposed to attain dense compression of fuel and improve laser‐core coupling efficiency by adopting double‐cone structure, a low‐density inner liner, low‐Z outer coating, and Br‐doped fuel shell. In this paper, present status and near term prospects of the FIREX‐I project will be reported together with activities on target designing, laser development, and plasma diagnostics.AIP Conference Proceedings. 02/2010; 1209(1):83-86. -
Article: Plasma physics and laser development for the Fast-Ignition Realization Experiment (FIREX) Project
[show abstract] [hide abstract]
ABSTRACT: Since the approval of the first phase of the Fast-Ignition Realization Experiment (FIREX-I), we have devoted our efforts to designing advanced targets and constructing a petawatt laser, which will be the most energetic petawatt laser in the world. Scientific and technological improvements are required to efficiently heat the core plasma. There are two methods that can be used to enhance the coupling efficiency of the heating laser to the thermal energy of the compressed core plasma: adding a low-Z foam layer to the inner surface of the cone and employing a double cone. The implosion performance can be improved in three ways: adding a low-Z plastic layer to the outer surface of the cone, using a Br-doped plastic ablator and evacuating the target centre. An advanced target for FIREX-I was introduced to suit these requirements. A new heating laser (LFEX) has been constructed that is capable of delivering an energy of 10 kJ in 10 ps with a 1 ps rise time. A fully integrated fast-ignition experiment is scheduled for 2009.Nuclear Fusion 09/2009; 49(10):104024. · 4.09 Impact Factor -
Article: Fabrication of aerogel capsule, bromine-doped capsule, and modified gold cone in modified target for the Fast Ignition Realization Experiment (FIREX) Project
[show abstract] [hide abstract]
ABSTRACT: The development of target fabrication for the Fast Ignition Realization EXperiment (FIREX) Project is described in this paper. For the first stage of the FIREX Project (FIREX-I), the previously designed target has been modified by using a bromine-doped ablator and coating the inner gold cone with a low-density material. A high-quality bromine-doped capsule without vacuoles was fabricated from bromine-doped deuterated polystyrene. The gold surface was coated with a low-density material by electrochemical plating. For the cryogenic fuel target, a brand new type of aerogel material, phloroglucinol/formaldehyde (PF), was investigated and encapsulated to meet the specifications of 500 µm diameter and 20 µm thickness, with 30 nm nanopores. Polystyrene-based low-density materials were investigated and the relationship between the crosslinker content and the nanopore structure was observed.Nuclear Fusion 09/2009; 49(9):095028. · 4.09 Impact Factor -
Article: Shock Hugoniot and temperature data for polystyrene obtained with quartz standard
[show abstract] [hide abstract]
ABSTRACT: Equation-of-state data, not only pressure and density but also temperature, for polystyrene (CH) are obtained up to 510 GPa. The region investigated in this work corresponds to an intermediate region, bridging a large gap between available gas-gun data below 60 GPa and laser shock data above 500 GPa. The Hugoniot parameters and shock temperature were simultaneously determined by using optical velocimeters and pyrometers as the diagnostic tools and the α-quartz as a new standard material. The CH Hugoniot obtained tends to become stiffer than a semiempirical chemical theoretical model predictions at ultrahigh pressures but is consistent with other models and available experimental data.Physics of Plasmas 06/2009; 16(6):062702-062702-6. · 2.15 Impact Factor -
Article: Study on a fuel layering sequence of the foam target for the FIREX project
[show abstract] [hide abstract]
ABSTRACT: To develop the fuel layering sequence for the FIREX cryogenic target, redistribution of surrogate fuel, solid H2 in a shell with cooling duration has been studied. Two kinds of dummy targets with a foam and a polystyrene shells (~800 μm and 2 mm in diameter, respectively) were tested. The solid H2 layer in the polystyrene shell was accumulated on the shell bottom as time elapsed. On the other hand, the foam shell had less elapsed time dependence than the polystyrene shell. Furthermore, elapsed time appeared to make the solid H2 layer uniform.Journal of Physics Conference Series 06/2008; 112(3):032067. -
Article: Developments of characterization of the foam shell target for fast ignition realization experiment-I (FIREX-I)
[show abstract] [hide abstract]
ABSTRACT: Equipments and techniques have been developed for characterization of the foam shell target for the FIREX-I. An interference measurement technique is planned to use to measure the quantity of fuel in a foam shell. A preliminary experiment of the interference measurement technique was carried out. Experimental results indicate the refractive index of RF foam is near 1.08 and that of vacant RF foam containing liquid H2 is near 1.22. Calculations indicate the refractive index of vacant RF foam is 1.07 and that of RF foam containing H2 is 1.19. Some causes of these differences were discussed.Journal of Physics Conference Series 06/2008; 112(3):032066. -
Conference Proceeding: Encapsulation of Low Density Materials for the First Stage of Fast Ignition Realization Experiment (FIREX-I) - Control of Microstructure and Gelation Process using a Phase-Transfer Catalyst and Tailored Polymers
[show abstract] [hide abstract]
ABSTRACT: Development of foam capsule fabrication for cryogenically cooled fuel targets is overviewed in the present paper. The fabrication development was initiated as a part of the Fast Ignition Realization Experiment (FIREX) project at the ILE, Osaka University in the way of bilateral collaboration between Osaka University and national institute for fusion science (NIFS). For the first stage of FIREX (FIREX-1), a foam cryogenic target was designed where low-density foam shells with a conical light guide will be cooled down to the cryogenic temperature and will be fueled through a narrow pipe. The required diameter and thickness of the capsule are 500 mum and 20 mum, respectively. The material should be low-density plastics foam. We have prepared such capsules using 1) new material of (phloroglucinolcarboxylic acid)/formalin resin to control kinematic viscosity of the precursor, 2) phase-transfer-catalyzed gelation process to keep density matching of three phases of the emulsion. 3) non-volatile silicone oil as outer oil of emulsion in order to prevent hazard halogenated hydrocarbon and flammable mineral oil. The obtained foam capsule had fine structure of 180 nm (outer surface) to 220 nm (inner surface) and uniform thickness reaching to resolution limit of optical analysis (~0.5 mum). A small hole was made before the solvent exchange and the drying process to prevent distortion due to volume changes. The density of dried foam was 0.29 g/cm . After attaching the petawatt laser guiding cone and fueling glass tube, poly([2,2]paracyclophane) was coated on the foam surface and supplied for a fueling test of cryogenic hydrogen.Fusion Engineering, 2007. SOFE 2007. 2007 IEEE 22nd Symposium on; 07/2007 -
Article: Achievement of high availability in long-term operation and upgrading plan of the LHD superconducting system
[show abstract] [hide abstract]
ABSTRACT: The Large Helical Device (LHD) is not only the largest stellarator for the research of fusion plasma near a reactor region but also the largest superconducting system. Availability higher than 98% has been achieved in the long-term continuous operation both in the cryogenic system and in the power supply system. It is due to the robustness of the systems and efforts of maintenance and operation. One big problem is the shortage of cryogenic stability of a pair of pool-cooled helical coils. Composite conductors had been developed to attain sufficient stability at high current density. However, it was revealed that a normal-zone could propagate below the cold-end recovery current by additional heat generation due to the slow current diffusion into a thick pure aluminium stabilizer. Besides, a novel detection system with pick-up coils along the helical coils revealed that normal-zones were initiated near the bottom of the coil where the field is not the highest. Therefore, the cooling condition around the innermost layers, the high field area, will be deteriorated at the bottom of the coil by bubbles gathered by buoyancy. In order to raise the operating currents, methods for improving the cryogenic stability have been examined and stability tests have been carried out with a model coil and small coil samples. We selected a method to lower temperatures of the coil and an additional cooler has been installed at the inlet of the coil. The outlet temperatures of the coil have been successfully lowered to 3.8 from 4.4 K of the saturated temperature, as planned.Nuclear Fusion 03/2007; 47(4):353. · 4.09 Impact Factor -
Article: Improvement in Cryogenic Stability of the Model Coil of the LHD Helical Coil by Lowering the Temperature
[show abstract] [hide abstract]
ABSTRACT: Helical coils of the Large Helical Device are pool-cooled superconducting magnets, in which propagation of a normal-zone has been observed several times at about 86% of the nominal current of 13.0 kA. It is planned to improve the cryogenic stability by lowering the inlet temperature. In order to estimate the effect, the cryogenic stability of a model coil of the helical coil was examined in saturated and subcooled helium. Liquid helium is supplied from the bottom of the model coil, and it is exhausted through the winding to the current-leads tank. The inlet helium is subcooled by a pre-cooler. A normal zone was initiated by a heater on the conductor at the bottom of the coil. In saturated helium of 4.4 K and 0.12 MPa, the minimum current to propagate over the next turn varies from 10.7 to 11.2 kA in the four cases that are without or with additional thermal shields, and before or after being subcooled. The difference is considered to be caused by the change of quality of saturated helium inside the winding or by the change of the wetted condition of the conductor surface. The minimum currents are higher at the lower temperatures in subcooled helium. It is raised up to 11.7 kA at 3.5 K of the temperature inside the winding. The propagation velocity at each minimum current is almost same. Namely, the propagation velocities at the same current are slower at the lower temperature in subcooled heliumIEEE Transactions on Appiled Superconductivity 07/2006; · 1.04 Impact Factor -
Article: Temperature dependence of the mechanical properties of melt-processed Dy–Ba–Cu–O bulk superconductors evaluated by three point bending tests
[show abstract] [hide abstract]
ABSTRACT: Dy–Ba–Cu–O bulk superconductor has an excellent capability of trapping magnetic flux and lower heat conductivity at cryogenic temperatures as compared with Y–Ba–Cu–O bulk superconductor. The Young's modulus and the bending strength in the range from room temperature to 7 K were measured by the three-point bending tests using specimens cut from a melt-processed Dy–Ba–Cu–O bulk superconductor. They were tested in a helium gas flow type cryostat at Forschungszentrum Karlsruhe and in a liquid nitrogen bath at Iwate University. The Young's modulus was calculated by either the slope of stress–strain curve or that of the load–deflection curve of the specimen. Although the bending strength measured in the two institutes coincided well, there was a significant discrepancy in the Young's modulus. The Young's modulus and bending strength increased with decrease of temperature down to 7 K. The amount of increase in the Young's modulus and the bending strength were about 32% and 36% of those at room temperature, respectively. The scatter of data for each run was significant and did not depend on temperature. The temperature dependence of the Young's modulus coincided with that in Y–Ba–Cu–O obtained by ultrasonic velocity. The temperature dependence of the Young's modulus and the bending strength was discussed from the view point of interatomic distance of the bulk crystal.Superconductor Science and Technology 05/2006; 19(7):S545. · 2.66 Impact Factor -
Article: Foam materials for cryogenic targets of fast ignition realization experiment (FIREX)
[show abstract] [hide abstract]
ABSTRACT: Development of foam materials for cryogenically cooled fuel targets is described in this paper. The fabrication development was initiated as a part of the fast ignition realization experiment (FIREX) project at the ILE, Osaka University under a bilateral collaboration between Osaka University and National Institute for Fusion Science (NIFS). For the first stage of FIREX (FIREX-I), a foam cryogenic target was designed in which low-density foam shells with a conical light guide will be fuelled through a narrow pipe and will be cooled down to the cryogenic temperature. Acrylic polymer, resorcinol–formaldehyde (RF) resin, poly(4-methyl-1-pentene) (PMP), and polystyrene-based crosslinking polymer have been investigated as supporting materials for cryogenic fuel. The properties of the material and the present status of the material development are summarized.Nuclear Fusion 10/2005; 45(11):1277. · 4.09 Impact Factor -
Article: Asymmetrical normal-zone propagation observed in the aluminum-stabilized superconductor for the LHD helical coils
[show abstract] [hide abstract]
ABSTRACT: Transient normal-transitions have been observed in the superconducting helical coils of the Large Helical Device (LHD). Stability tests have been performed for an R&D coil as an upgrading program of LHD, and we observed asymmetrical propagation of an initiated normal-zone. In some conditions, a normal-zone propagates only in one direction along the conductor and it hence forms a traveling normal-zone. The Hall electric field generated in the longitudinal direction in the aluminum stabilizer is a plausible candidate to explain the observed asymmetrical normal-zone propagation.IEEE Transactions on Appiled Superconductivity 07/2004; · 1.04 Impact Factor -
Article: Development of 1.8 K HTS current feedthrough using large-sized YBCO bulk conductors
[show abstract] [hide abstract]
ABSTRACT: In Phase II experiment of a large helical device (LHD) of the National Institute for Fusion Science (NIFS), the helical coils are planned to be operated at 1.8 K by employing pressurized superfluid cooling to raise the magnetic field up to 4 T using a current of 17.3 kA. It is important to develop a 20 kA-class current feedthrough into the 1.8 K region with high current capacity and low heat leakage in the maximum leakage magnetic field of 1 T. The YBCO bulk conductors of 20 mm in width, 140 mm in length and 10 mm in thickness were assembled into a prototype 1.8 K current feedthrough. The current transport tests of the prototype 1.8 K current feedthrough were carried out successfully for currents up to 20 kA with liquid helium bath cooling at 4.2 K. The transport current was held at 20 kA for longer than 300 seconds. During the 20 kA operation, the current transport section of the YBCO bulk conductor remained in the superconducting state and the voltage drop between the YBCO bulk conductors and the copper electrode was constant. The contact resistance and the Joule heat generation in the joint region between the YBCO bulk conductors and the copper electrode were 1.8 nΩ and 0.72 W, respectively when operated at 20 kA. We demonstrated the feasibility of a 1.8 K HTS current feedthrough using large-sized YBCO bulk conductors for the Phase II experiment of the LHD.IEEE Transactions on Appiled Superconductivity 07/2004; · 1.04 Impact Factor -
Article: Measurement of superconductor motion in R&D coil for supercooling of the LHD helical coil
[show abstract] [hide abstract]
ABSTRACT: A superconducting solenoid coil was constructed using a large-scale superconductor to investigate the stability of helical coil in the Large Helical Device. The coil was cooled down to 3.2-4.4 K and current of 13 kA was put in. Superconductor motion was detected directly with a high sensitivity displacement gage. At the center of the magnet, the conductor expanded to outside stably, but the conductor at the corner showed contrary and incomprehensible behavior expected the conductor rotation due to mismatching to the magnetic field.IEEE Transactions on Appiled Superconductivity 07/2004; · 1.04 Impact Factor -
Article: Experimental apparatus for measuring the characteristics of HTS coils under controllable magnetic field, orientation and temperature
[show abstract] [hide abstract]
ABSTRACT: The electric field vs. current density (E-J) characteristics of high temperature superconducting (HTS) tapes strongly depend on the magnetic field, its orientation and operation temperature. In order to investigate the current distribution and electromagnetic phenomena in HTS tapes, we have developed an experimental apparatus which can measure the characteristics of HTS tapes under various conditions of magnetic field (0-5 T), its orientation and temperature (10-150 K). The magnetic field is generated by cryocooler-cooled superconducting split coils. The field strength as well as its orientation can be freely varied in the sample space (diameter 150 mm, height 30 mm) by controlling the current and its direction of each coil. By applying HTS current-leads with Au-doped Ag-sheathed Bi-2223 tapes for the split coils (100 A) as well as for the sample coil (500 A), the heat in-leak is sufficiently reduced, and hence a flexible experiment without using liquid helium is enabled.IEEE Transactions on Appiled Superconductivity 07/2004; · 1.04 Impact Factor -
Article: Sawtooth oscillation in current-carrying plasma in the large helical device.
[show abstract] [hide abstract]
ABSTRACT: Sawtooth oscillations have been observed in current-carrying helical plasmas by using electron-cyclotron-emission diagnostics in the Large Helical Device. The plasma current, which is driven by neutral beam injection, reduces the beta threshold of the sawtooth oscillation. When the central q value is increased due to the plasma current, the core region crashes, and, when it is decreased, the edge region crashes annularly. Observed rapid mixture of the plasma in the limited region suggests that these sawtooth crashes are reconnection phenomena. Unlike previous experiments, no precursor oscillation has been observed.Physical Review Letters 06/2003; 90(20):205001. · 7.37 Impact Factor
Top co-authors
Top Journals
Institutions
-
1997–2011
-
National Institute for Fusion Science
Toki, Gifu-ken, Japan
-
-
2007
-
Osaka University
- Institute of Laser Engineering
Ōsaka-shi, Osaka-fu, Japan
-
-
2000–2002
-
Tokai University
- School of Engineering
Hiratsuka, Kanagawa-ken, Japan -
Kyushu University
Fukuoka-shi, Fukuoka-ken, Japan
-
-
1999
-
Kagoshima University
Kagoshima-shi, Kagoshima-ken, Japan
-
