Y. Kozaki

National Institute for Fusion Science, Tokitsu-chō, Gifu, Japan

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Publications (38)13.2 Total impact

  • [Show abstract] [Hide abstract] ABSTRACT: We organized a design committee for the laser fusion experimental reactor to show the feasibility to construct it with existing materials and improved technologies. The issue includes the coupling efficiency and target injection.
    No preview · Conference Paper · Jun 2013
  • Masahiro TANAKA · Takuya GOTO · Yasuji KOZAKI · Akio SAGARA
    [Show abstract] [Hide abstract] ABSTRACT: Tritium particle balance in the FFHR DEMO reactor is investigated with consideration of the fueling efficiency by pellet injection system, retention loss in a vacuum vessel and permeation loss from the fuel processing system. In order to satisfy the fuel balance and the tritium safety management, it was necessary to suppress the tritium retention rate to be 10-5 and the DFs in the tritium cycle systems to above 107with the tritium breeding ratio of 1.08. The processing throughput for the tritium processing system is estimated to be about 400 mol/h, which is almost same as the throughput of the fuel stream for the ITER. Therefore, the tritium processing system for vacuum exhaust gas for the DEMO will not be necessary to improve the system for the ITER further. On the other hands, the significant development of the tritium processing system for the effluent disposal and the waste materials from the safety aspect and the social acceptance will be required toward the DEMO reactor. © 2012 The Japan Society of Plasma Science and Nuclear Fusion Research.
    No preview · Article · Jan 2012 · Plasma and Fusion Research
  • [Show abstract] [Hide abstract] ABSTRACT: This paper presents a proposal of the remote participation system for the international thermonuclear experimental reactor (ITER). The object of this paper is to clarify technical issues to analyze the ITER data safely and conveniently. The Japanese case is considered as an example, but technologies presented here can be used worldwide. Major technical issues are as follows: (1) the long distance data transfer; (2) the massive data server; (3) the secure network; (4) the convenient and fast data analysis system. Raw data of ITER can be transferred from France to Japan in a short time by optimizing TCP/IP parameters. The virtual private network (VPN) technology provides a secure environment of the data mirroring and the distributed computation. The analysis server with the WEB user interface enables physicists to analyze the ITER data from the Internet. Streaming data, such as plasma parameters in the steady state, video and sound of the ITER plasma and the status of experiment, which provides feeling of reality, are delivered by using the multi-cast technology. These technologies are being developed in SNET, which is a virtual laboratory for Japanese fusion community. International collaboration is required to develop a global distributed file system and a data analysis system further.
    No preview · Article · Jul 2010 · Fusion Engineering and Design
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    Y. Kozaki · S. Imagawa · A. Sagara
    [Show abstract] [Hide abstract] ABSTRACT: Based on the recent experiment results of LHD and the magnet technology-cost basis developed for ITER construction, the design window of helical reactors are analyzed. For searching design windows and investigating their economical potential, we have developed a mass-cost estimating model linked with system design code (HeliCos). We found that the LHD-type helical reactor has the technically and economically attractive design windows, where the major radius is increased as large as for the sufficient blanket space, but the magnetic stored energy is decreased to reasonable level because of lower magnetic field with the convenient physics basis of H factor near 1.1 to the ISS04 scaling and beta value of 5%.
    Full-text · Article · Sep 2009 · Nuclear Fusion
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    [Show abstract] [Hide abstract] ABSTRACT: Progress of design studies on a heliotron reactor is reported. Recent experimental achievements in large helical device (LHD) are building up the physical basement. Integrated designs on LHD-type energy reactors have improved the base design of force free helical reactor and revealed economical feasibility. Large helical device is exploring a new horizon of net current free helical plasmas. Inherent characteristics demonstrate reactor relevant performances individually; steady state (1 h), high beta (5%), high density (1 × 1021 m−3), etc. In particular, discovery of internal diffusion barrier provides a novel attractive scenario of super high density operation. It greatly facilitates physical requirements as well as mitigates engineering demands. New methods have been proposed to access and operate ignited plasmas; a long rise-up over 300 s to reduce the heating power to 30 MW and a new proportional-integration-derivative (PID) control of the fueling to handle the thermally unstable plasma at high-density operations.
    Full-text · Article · Dec 2008 · Fusion Engineering and Design
  • T Kunugi · T. Nakai · Z. Kawara · T. Norimatsu · Y. Kozaki
    [Show abstract] [Hide abstract] ABSTRACT: To protect the first wall of an inertia fusion reactor from extremely high heat flux, X-rays, alpha particles and fuel debris caused by a nuclear fusion reaction, a “cascade-type” falling liquid-film flow is proposed as a “liquid-wall” concept. The flow visualization experiment to investigate the feasibility of this liquid-wall concept has been conducted. The preliminary numerical simulation results suggest that the current cascade structure design should be improved because less thermal-mixing is expected. The cascade-type structure has, therefore, been redesigned. This new cascade-type first wall consists of a liquid reservoir which has a free-surface to maintain a constant water head in the rear, and connects to a slit composed of two plates, i.e., the first wall is connected to a slit which is partially made up of the first wall to begin with it. The numerical simulations were performed on the new cascade-type first wall and they show the stable liquid-film flow on it. Moreover, the POP (proof-of-principle) flow visualization experiments, which satisfy the Weber number coincident condition, are carried out using water as the working fluid. By comparing the numerical and experimental results, it was found that the liquid-film flow with 3–5mm thickness could be stably established. According to these results for the new cascade-type first wall concept, it was confirmed that the coolant flow rate and the thickness of the liquid-film could be controlled if the Weber number coincident condition was satisfied.
    No preview · Article · Dec 2008 · Fusion Engineering and Design
  • [Show abstract] [Hide abstract] ABSTRACT: Recent activities on optimizing the base design of the large helical device (LHD)-type helical reactor FFHR (force free helical reactor) are presented. Three candidates to secure the blanket space are proposed with the aim of reactor size optimization without deteriorating α-heating efficiency and by taking cost analyses into account. In this way the key engineering aspects are investigated; from 3D blanket designs, it is demonstrated that the peaking factor of the neutron wall loading is 1.2–1.3 and a blanket covering ratio of over 90% is possible by proposing discrete pumping with a semi-closed shield (DPSS) concept. Helical blanket shaping along the divertor field lines is the next big issue. For large superconducting magnet systems under the maximum nuclear heating of 200 W/m3, cable-in-conduit conductor (CICC) and alternative conductor designs are proposed with a robust design of cryogenic support posts. For access to ignited plasmas, new methods are proposed, in which a long rise-up time over 300 s reduces the heating power to 30 MW and a new proportional-integration-derivative (PID) control of the fueling can handle the thermally unstable plasma at high-density operation. This paper focuses on FFHR2m1, which is a modified version of FFHR.
    No preview · Article · Dec 2008 · Fusion Engineering and Design
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    Shinsaku Imagawa · Akio SAGARA · Yasuji KOZAKI
    [Show abstract] [Hide abstract] ABSTRACT: LHD-type reactors have attractive features for fusion power plants, such as no requirement of a current drive and a wide space between the helical coils for the maintenance of in-vessel components. One disadvantage was considered the requirment of a large major radius to attain the self-ignition condition with a sufficient space for blankets. According to the recent reactor studies based on experimental results in LHD, the major radius of plasma is set at 14 to 17 m with the central toroidal field of 6 to 4 T. The stored magnetic energy is estimated at 120 to 130 GJ. Both the major radius and the magnetic energy are about three times as large as those for ITER. We intend to summarize the requirements for superconducting magnets of the LHD-type reactors and propose a conceptual design of the magnets with cable-in-conduit (CIC) conductors based on the technology for ITER.
    Full-text · Article · Jan 2008 · Plasma and Fusion Research
  • [Show abstract] [Hide abstract] ABSTRACT: Recent progress on fast ignition (FI) and cooled Yb:YAG ceramic laser enable us to design an IFE power plant with a 1 MJ-class, compact laser whose output energy is 1/4 of previous central ignition scheme. Basing on the F1 scheme, we conceptually designed a laser fusion power plant driven with cooled-Yb:YAG, ceramic lasers. The cooled Yb-YAG ceramic was newly chosen as the laser material. We found that the heating laser for ignition could be constructed with the cooled Yb: YAG ceramics as well as the compression laser with acceptable electricity-laser conversion efficiencies including the electric power for the cooling system. A new reactor scheme for a liquid wall reactor that has no stagnation point of ablated gas was proposed.
    No preview · Article · Nov 2007 · Fusion Science and Technology
  • K. Tomabechi · Y. Kozaki · T. Norimatsu
    [Show abstract] [Hide abstract] ABSTRACT: A conceptual design of the laser fusion reactor KOYO-F based on the fast ignition scheme is reported including the target design, the laser system and the design for chamber. A Yb-YAG ceramic laser operated at 200K is the primary candidate for the compression laser and an OPCPA system is the one for the ignition laser. The chamber is basically a wet wall type but the fire position is vertically off-set to simplify the protection scheme of the ceiling. The target consists of foam insulated, cryogenic DT shells with a LiPb, reentrant guide-cone.
    No preview · Article · Jun 2006 · Journal de Physique IV (Proceedings)
  • [Show abstract] [Hide abstract] ABSTRACT: We have carried out the design studies of KOYO-Fast laser fusion power plant, using fast ignition cone targets, DPSSL lasers, and LiPb liquid wall chambers. Using fast ignition targets, we could design a middle sized 300 MWe reactor module, with 200 MJ fusion pulse energy and 4 Hz rep-rates, and 1200MWe modular power plants with 4 reactor modules and a 16 Hz laser driver. The liquid wall chambers with free surface cascade flows are proposed for cooling surface quickly enough to a 4 Hz pulse operation. We examined the potential of Yb-YAG ceramic lasers operated at $150\sim 225$ K for both implosion and heating laser systems required for a 16-Hz repetition and 8 % total efficiency.
    No preview · Article · Jun 2006 · Journal de Physique IV (Proceedings)
  • [Show abstract] [Hide abstract] ABSTRACT: We have developed a simulation code to treat behaviors of wall ablation by X-rays, α particles and charged particles from fusion burning targets. The absorption of energy of α particles and charged particles by ablated wall plasmas was estimated using the stopping power obtained by dielectric functions of plasmas and Bethe formulas. We show that ablated wall material (Pb) moves as clump. We clarify that the screening effects of charged particles expanding from fusion burning by ablated wall material (Pb) decrease the ablation depth of liquid Pb compared with that of no screening effects.
    No preview · Article · Oct 2005 · Fusion Engineering and Design
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    [Show abstract] [Hide abstract] ABSTRACT: This is the review on the laser fusion research at Institute of Laser Engineering of Osaka University. Since 1996, we have concentrated our efforts on fast ignition laser fusion research. By constructing 100 TW and 1Peta watt lasers, experiments on relativistic laser plasma interactions related to fast ignition and pellet implosion and heating have been carried out. The results indicate that imploded core plasma is heated with relatively high coupling efficiency. According to the above results, we started the FIREX (Fast Ignition Realization Experiment) project for demonstrating ignition and burn with a multi 10kJ short pulse laser. The future prospects of the project are presented in this paper.
    Preview · Article · Apr 2005 · Fusion Science and Technology
  • [Show abstract] [Hide abstract] ABSTRACT: Various candidate materials were irradiated with intense proton beams at Yokohama campus of Tokyo Institute of Technology (TITech), and some others were irradiated with intense nitrogen beams at Albuquerque site of Sandia National Laboratories (SNL). Intense X-rays of SNL were also used to irradiate other materials. A series of numerical calculations of X-ray ablations was additionally performed at TITech, which results were compared with the experimental ones. Our aims were to supply necessary data for the future design of inertial fusion reactor chambers. One of the key issues in this field was the ablation thickness of the various chamber wall materials with typical inertial fusion reactions. We measured the ablation thickness of various samples, and we also observed the surface conditions of the samples before and after the irradiations with a microscope and an X-ray luminescence composition analyzer. Associated technical issues for the subject including UV-laser ablation, in-situ measurement of ablated thickness and a few new ion sources were also mentioned in short.
    No preview · Article · Jan 2004
  • Akio Sagara · Mikio Enoeda · Satoshi Nishio · Yasuji Kozaki
    [Show abstract] [Hide abstract] ABSTRACT: The main functions of the blanket in fusion power reactors are basically independent of the type of magnetic fusion reactor (tokamak, helical, etc.) and inertia fusion. However, from technical point of view, many candidate designs of blanket have been proposed depending on the particular reactor concepts. Their main features are characterized for the recent typical designs, and key issues are defined.
    No preview · Article · Jan 2003 · Journal of Plasma and Fusion Research
  • [Show abstract] [Hide abstract] ABSTRACT: Simulation studies on evacuation process in liquid wall chamber have been carried out. The evacuation speed in wetted wall concepts is a critical issue for pulse repetition rate. Then we have analyzed the evacuation process in high vacuum region using the DSMC code, which solves the Boltzmann equation. The simulation results of the DSMC code show that the effect of viscosity can't be neglected in the region where the gas pressure goes down to 10−3–10−4 Torr, near the saturated vapor pressure. When the surface temperature of liquid wall is adequately cooled, the evacuation speed from 10−2 to 10−4 Torr is rather fast because of the gas flow to the wall.
    No preview · Article · Jan 2002 · Fusion Engineering and Design
  • Y Kozaki
    [Show abstract] [Hide abstract] ABSTRACT: A brief review is given of the objectives and conditions required to realize inertial fusion energy (IFE) power plants. Using a general system design code, an analysis of design windows for obtaining economically attractive IFE power plants is carried out. There are many options for IFE concepts — target irradiation, target heating, drivers and reaction chamber. In these combinations, the concepts that use laser for direct drive are considered the most promising approach because of the potential for achieving high gain targets and the recent progress of diode pumped solid state lasers. We analyzed the IFE development programs using network analysis methods. The results of the analysis show that the independence and modular characteristic of the IFE key system, such as laser and reaction chamber, could make IFE projects rather small in size and easy to promote with a step by step program. Therefore, the way to the ICF reactor is very flexible in decreasing the risks and selecting the optimum choice from a wide variety of options.
    No preview · Article · Nov 2000 · Fusion Engineering and Design
  • [Show abstract] [Hide abstract] ABSTRACT: Using the theories of photon count statistic and test data of the ultraweak photon emission from biological system, the biophoton field's spectra distribution properties were studied in this paper. An experimental setup for testing UPE in different spectral region were designed. The test data proved UPE of living biological system exists in wide spectra region from UV-visible to IR. Using the test data, we can obtain important conclusions that is UPE almost has nothing to do with wavelength. The conclusion has important significance for proving the bio-photon coherence. In the end of this paper, the medical applications of UPE in 21st century were discussed simply.
    No preview · Article · Jan 2000 · Proceedings of SPIE - The International Society for Optical Engineering
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    [Show abstract] [Hide abstract] ABSTRACT: The progress of implosion physics research and relevant technologies enable us to examine technical and economical feasibility, and to plan the realistic strategy to the commercial power plant. The most important key issue for IFE is the driver technology. The development of the laser fusion driver is opening new industrial technologies based on the photon processes and new fields of high energy physics.
    Full-text · Article · Sep 1998 · Proceedings of SPIE - The International Society for Optical Engineering
  • Y. Kozaki · S. Imagawa · A. Sagara
    No preview · Article ·