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A hybrid quantum cascade laser/Fe:ZnSe amplifier system for power scaling of CW lasers at 4.0–4.6 µm
Get PDF0000-0001-6930-0843A hybrid continuous-wave Fe:ZnSe laser amplifier seeded with a mid-infrared quantum cascade laser is demonstrated. A maximum output power of 870 mW with an extraction efficiency of 30 % was achieved from the Fe:ZnSe amplifier seeded by a 200-mW laser at 4.0 µm, corresponding to a gain of approximately 4.4. When the amplifier was seeded by a 150-mW laser at 4.6 µm, an effective gain of approximately 1.4 was obtained. Additionally, we present a theoretical analysis to provide possible routes for further optimization of this Fe:ZnSe amplifier system.journal articl
Behavior of geodesic acoustic mode and limit-cycle oscillation approaching L-H transition in JFT-2M tokamak
Get PDF0000-0001-5669-1937In this paper, a phenomenology of competing behavior between the geodesic acoustic mode (GAM) and the limit-cycle oscillation (LCO) is presented. Before the LCO occurs, the GAM can grow to the observable amplitude via the turbulent Reynolds stress force. Approaching the L-H transition, the LCO is excited and the GAM decays. In the LCO phase, the GAM driving force is possibly suppressed by the nonlocal turbulence amplitude modulation by the LCO.journal articl
多要素認証の認証コード通知を偽ったSMSの調査と対応
No full text0000-0001-5888-8901核融合科学研究所ではMicrosoft 365 for Education A3を契約し，認証方式にSMSなどを用いた多要素認証を必須としている．2021年12月に利用者からNIFS-CSIRTに対し中国語の意図せぬマイクロソフトの認証コード通知のSMSが着信したとの報告があり，研究所全域に情報提供を呼びかけた結果，認証方式にSMSを設定している利用者の2割以上が意図せぬSMSを受信していたことが判明した．その後，Azure ADログの確認とマイクロソフト社へ問合せの結果，利用者情報の漏洩はないことを確認した．同社からはあわせて，長期的にはSMSなど公衆交換電話網を介在させる認証方式は避けた方がよい旨の助言があった．未だに根本的な原因は不明であるが，本稿では本事案の調査と対応について考察する．journal articl
Explosive boiling of liquid nitrogen in a long thin tube and its application to the detection of a local temperature rise
Get PDFTo promote the commercial use of high-temperature superconducting devices, the ability to detect temperature anomalies easily and reliably and thereby protect the devices is important. In particular, a sudden local temperature increase due to a superconducting-to-normal transition can damage a device. In the present study, we propose a method to detect explosive boiling of superheated liquid nitrogen sealed in a long thin tube using a pressure gauge connected to the end of the tube. Experiments using a stainless-steel tube with an inner diameter of 1 mm and a maximum length of 50 m under various conditions showed that the local temperature rise caused explosive boiling at a temperature slightly below the superheat limit of 110 K for liquid nitrogen; the results also showed that the rapid pressure increase was transmitted to the end of the tube at approximately the speed of sound (∼830 m/s). The proposed method of placing a thin tube along high-temperature superconducting conductors or cryogenic structures can be used to easily detect a local temperature rise.journal articl
Development of the Q-band ECE imaging system in the large helical device
Get PDFIn this study, we developed the Electron Cyclotron Emission Imaging (ECEI) system with the Q-band in the Large Helical Device (LHD). ECEI measurement makes it possible to obtain the spatiotemporal structure of magnetohydrodynamics (MHD) instabilities in the high-β plasma. Although there were several difficulties for realizing the multi-channelization, such as local oscillator (LO) optics and an expensive high-power LO source, we have solved these problems by developing a Local Integrated Antenna array (LIA) which has an internal LO supply, using a frequency doubler integrated circuit on each channel, instead of a conventional Horn-antenna Mixer Array (HMA) with common LOs. In addition, we have made some improvements to enhance the quality of the measurement signal. First, we developed and introduced notch filters that prevent the strong Electron Cyclotron Resonance Heating (ECRH) stray signal from being mixed into the measurement circuit. Second, the position of the doubler built in the printed circuit board was reconsidered to prevent the mixing of higher harmonic components into the mixer. Also, we have adopted the Logarithmic detector (LOG detector) to deal with the wide dynamic range of the plasma fluctuation. After these improvements, for the first time, we could successfully obtain the initial results of the two-dimensional temperature distribution and its fluctuation distribution in the LHD.journal articl
Recent results from deuterium experiments on the large helical device and their contribution to fusion reactor development
Get PDF0000-0001-5220-947XIn recent deuterium experiments on the large helical device (LHD), we succeeded in expanding the temperature domain to higher regions for both electron and ion temperatures. Suppression of the energetic particle driven resistive interchange mode (EIC) by a moderate electron temperature increase is a key technique to extend the high temperature domain of LHD plasmas. We found a clear isotope effect in the formation of the internal transport barrier in high temperature plasmas. A new technique to measure the hydrogen isotope fraction was developed in the LHD in order to investigate the behavior of the isotope mixing state. The technique revealed that the non-mixing and the mixing states of hydrogen isotopes can be realized in plasmas. In deuterium plasmas, we also succeeded in simultaneously realizing the formation of the edge transport barrier (ETB) and the divertor detachment. It is found that resonant magnetic perturbation plays an important role in the simultaneous formation of the ETB and the detachment. Contributions to fusion reactor development from the engineering point of view, i.e. negative-ion based neutral beam injector research and the mass balance study of tritium, are also discussed.journal articl
小特集：先進燃料核融合研究の現状と展開 ５．直線開放端磁場プラズマによる先進燃料核融合炉の研究例 ～ARTEMIS を振り返って～
Get PDF高ベータFRC を炉心プラズマに採用したD-3He 概念設計炉ARTEMIS について概説する．D-3He 炉はD-T
炉に本質的に備わる中性子の問題を根本から回避できる．その反面，プラズマ温度やプラズマ閉じ込めに課され
る厳しい条件を乗り越える必要があり，高ベータプラズマ閉じ込めが現実的な解となる．荷電粒子の高エネル
ギーを直接電気エネルギーへ変換する技術も高経済性を獲得するには必須であり，直接エネルギー変換器の導入
には直線型で開放端磁場構造を有する閉じ込め概念が適している．FRC や非断熱トラップがこれに該当する．
ARTEMIS とともに，現在検討を進めている連結非断熱トラップによるD-3He 核融合発電システムについても述
べる．journal articl
Clebsch representation of relativistic plasma and generalized enstrophy
Get PDF0000-0002-9344-4713The theory of relativistic plasmas is attracting interest as a model of high-energy astronomical objects. The topological constraints, built in the governing equations, play an essential role in characterizing the structures of plasmas. Among various invariants of ideal models, the circulation is one of the most fundamental quantities, being included in other invariants like the helicity. The conventional enstrophy, known to be constant in a two-dimensional flow, can be generalized, by invoking Clebsch variables, to the topological charge of a three-dimensional fluid element, which essentially measures circulations. Since the relativistic effect imparts space-time coupling into the metric, such invariants must be modified. The non-relativistic generalized enstrophy is no longer conserved in a relativistic plasma, implying that the conservation of circulation is violated. In this work, we extend the generalized enstrophy to a Lorentz covariant form. We formulate the Clebsch representation in relativity using the principle of least action and derive a relativistically modified generalized enstrophy that is conserved in the relativistic model.journal articl
Beam instability in the vicinity of beam extraction region of negative ion source
Get PDF0000-0002-5892-6047Beam instability in the presheath region of negative ion beam extraction is investigated in theoretically and experimentally. The linear stability analysis shows that the beam instability is unstable due to coupling between positive ion flow and negative ion flow. On the other hand, no clear activity can be seen in the experiment in the frequency range predicted by the theory. The beam instability in the presheath region of negative ion beam extraction may not cause the degradation of the beam focusing because of collisional damping and/or Landau damping.journal articl
Study on development policy for new cryogenic structural material for superconducting magnet of fusion reactor
Get PDFA fusion DEMO will require large-scale cryogenic structure including TF coil cases. Because of huge electromagnetic forces, extra thick plates and/or wrought products will be supplied. Since the midsection of the huge block is weaker than the block surface region, the design yield stress must be determined taking account of this lower strength part. To search the manufacturing process to improve the midsection strength, the crystal refinement strengthening and the precipitation strengthening are considered together with the carbon and nitrogen solid solution strengthening. XM-19 was focused based on the variation of the yield stress and the fracture toughness, a 100 mm thick block and a 30 mm thick plate were trial produced, and strength and the fracture toughness at the midsection were evaluated. This study will present the experimental data and discuss the development policy for a new cryogenic structural material for a fusion reactor.journal articl