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小特集：磁場閉じ込め核融合装置における水素原子分子輸送研究の新展開 ２．要素モデルの統合が実現する壁から プラズマまでを含めた中性粒子輸送研究
Get PDF非接触をはじめとするダイバータプラズマの諸現象を理解するため，壁での粒子リサイクリング，荷電粒
子，中性粒子を扱うコードの統合を進めている．水素分子には，電子状態のほか，回転および振動の内部自由度
があり，分子活性化再結合をはじめとするプラズマ中の水素分子の各種の反応速度係数は，水素分子の始状態の
振動・回転量子数により，数桁にわたって変化する．また，低温のプラズマでは，プラズマ中の電子やプロトン
衝突による水素分子の振動・回転励起がプラズマのエネルギー損失チャンネルとして重要と考えられる．このた
め，水素分子の振動・回転状態を中性粒子やプラズマの輸送と組み合わせて解く統合モデルを開発した．journal articl
小特集：磁場閉じ込め核融合装置における水素原子分子輸送研究の新展開 ３．表面分析と分光計測によって明らかになった 水素原子分子の炉内分布と輸送
Get PDF0000-0001-5045-9782プラズマ対向壁の水素吸蔵・放出を評価するための表面・再堆積層・バルクの水素輸送モデルとその
QUESTプラズマ対向壁への適用，およびその結果から構築した炉内粒子循環モデルとQUEST長時間放電に対す
る解析を紹介する．水素分子の発光スペクトル計測によるQUEST 第一壁近傍やLHD ダイバータ領域における水
素分子回転温度計測を紹介する．水素原子の発光スペクトル計測による周辺から炉心までの水素原子輸送ダイナ
ミクスの計測およびそのプラズマ閉じ込めとの関連について紹介する．journal articl
小特集：先進燃料核融合研究の現状と展開 ４．慣性核融合における先進燃料研究
Get PDF0000-0002-5738-4661慣性核融合における点火条件・燃焼率の簡易モデルによる評価に基づいて，DT 燃料と先進燃料（DD，
D3He，p11B）の比較を行い，先進燃料の特徴を概説する．また，近年，特に注目を集めているp11B 燃料について
は，従来の熱核融合反応だけでなく，非熱的核融合反応に着目したレーザー加速粒子を用いたレーザー実験や，
この反応を積極的に用いる点火方式などを紹介する．journal articl
Estimation of the Tritium Yields in Deuterium Fusion Plasmas Considering the Fast-Ion Velocity Distribution Function
Get PDF0000-0003-3293-488XTritium yields due to the deuterium-deuterium fusion reaction during the 22nd LHD experiment campaign are numerically estimated. As usual, the total tritium yields are assumed to be the same total neutron yields. In the Large Helical Device (LHD), however, it is considered that fusion reactivity of the D(d,p)T branch is lower than that of the D(d,n)3He one because the fusion reaction between a fast-deuteron and a thermal deuteron is dominant. By integrated simulation, considering the velocity distribution function of fast-deuteron, the ratio of the tritium yields to the neutron yields is estimated to be Yt/Yn ∼ 0.936. From the assumptions applied in the simulation, it is expected that this value should be still an over-estimation rather than the actual value.journal articl
Electro-optic Bdot probe measurement of magnetic fluctuations in plasma
Get PDF0000-0001-8457-5570We propose a combined use of a Pockels electro-optic sensor with a pickup loop coil (Bdot probe) for the measurement of magnetic fluctuations in plasmas. In this method, induced fluctuating voltage on the coil loop is converted into an optical signal by a compact electro-optic sensor in the vicinity of the measurement point and is transferred across optical fiber that is unaffected by electric noise or capacitive load issues. Compared with conventional Bdot probes, the electro-optic Bdot probe (1) is electrically isolated and free from noise pickup caused by the metallic transmission line and (2) can be operated at a higher-frequency range because of the smaller capacitance of the operation circuit, both of which are suitable for many plasma experiments. Conversely, the sensitivity of the current electro-optic Bdot probe arrangement is still significantly lower than that of conventional Bdot probes. A preliminary measurement result with the electro-optic Bdot probe showed the detection of a magnetic fluctuation signal around the cyclotron frequency range in the RT-1 magnetospheric plasma experiment.journal articl
磁場閉じ込めプラズマの乱流シミュレーション・データに対する画像を用いた解析
Get PDF0000-0002-1953-530X核融合研究は、持続可能な人類社会を支え得る究極のエネルギー源の実現を目指し、世界規模で進められている。磁場を用いた核融合炉では、約1 億度に熱せられた高温のプラズマをトーラス状の磁場で閉じ込めて、燃料となる重水素と三重水素の核融合反応によって生成するアルファ粒子によって燃料プラズマを自己加熱し、高温状態を維持しながら炉心の核融合反応を持続させる。核融合研究における数値シミュレーションは、高温プラズマ物理から装置壁との相互作用の物理まで多岐にわたる現象がその対象となるが、その中でも、炉心プラズマの輸送シミュレーションは最大規模の計算量を必要とする。これは、炉心プラズマが強い非平衡性を有するために、熱平衡分布ではなく位相空間上に複雑に分布した系を扱わねばならず、その第一原理モデルが、位相空間上の分布関数に対する発展方程式（ボルツマン方程式）に基づいているためである。磁場閉じ込め系では特に、異方性を持った強磁場の環境下であることを利用したジャイロ運動論[1]（粒子速度空間を3次元から磁場に垂直方向と平行方向の2次元に簡約した計5 次元の位相空間上の運動論モデル）と呼ばれるモデルが、大型計算機を用いたシミュレーション研究で広く利用されている。ジャイロ運動論シミュレーションでは、3 次元の実空間のみで記述される従来の流体モデルに比べて2 次元速度空間の分だけ自由度が増大し、1002 倍程度大きな計算量を必要とする。このシミュレーションが対象とする物理問題として、炉心プラズマ乱流に起因する熱輸送や燃料粒子輸送が挙げられるが、これらはプラズマ閉じ込め性能を左右するため、核融合炉の成立性に直結する最重要課題の一つとなっている。一方で近年では、スーパーコンピュータ「富岳」を始めとした大型計算機と計算技術の進歩によって、核融合プラズマの理論研究や定性的な物理研究のみならず、実験データ解析、乱流輸送モデル開発、さらには、炉心プラズマ設計など、具体的な核融合炉を見据えた定量的なシミュレーション研究が幅広く展開されている。本稿では、ジャイロ運動論シミュレーションから得られる5 次元位相空間の分布関数という巨大なデータに対する新しい解析手法として、特に可視化の観点から議論し、これまで見えてこなかったプラズマ乱流の側面を明らかにすべく、我々が進行している取り組みについて紹介する。journal articl
Data-Driven Control for Radiative Collapse Avoidance in Large Helical Device
Get PDFA radiative collapse predictor has been developed using a machine-learning model with high-density plasma experiments in the Large Helical Device (LHD). The model is based on the collapse likelihood, which is quantified by the parameters selected by the sparse modeling, including ne, CIV, OV, and Te,edge. The control system implementing this model has been constructed with a single-board computer to apply this predictor model to the LHD experiment. The controller calculates the collapse likelihood and regulates gas-puff fueling and boosts electron cyclotron resonance heating in real-time. In density ramp-up experiments with hydrogen plasma, high-density plasma has been maintained by the control system while avoiding radiative collapse. This result has shown that the predictor based on the collapse likelihood has the capability to predict a radiative collapse in real-time.journal articl
Inward diffusion driven by low frequency fluctuations in self-organizing magnetospheric plasma
Get PDF0000-0003-1088-8237The new findings for dynamic process of inward diffusion in the magnetospheric plasma are reported on the Ring Trap 1 (RT-1) experiment: (i) the evolution of local density profile in the self-organized process has been analyzed by the newly developed tomographic reconstruction applying a deep learning method; (ii) the impact of neutral-gas injection excites low-frequency fluctuations, which continues until the peaked density profile recovers. The fluctuations have magnetic components (suggesting the high-beta effect) which have two different frequencies and propagation directions. The phase velocities are of the order of magnetization drifts, and both the velocities and the intensities increase in proportion to the electron density. The self-regulating mechanism of density profile works most apparently in the naturally made confinement system, magnetosphere, which teaches the basic physics of long-lived structures underlying every stationary confinement scheme.journal articl
Linear-System Solver for EFG-Type Saddle-Point Problem without Using QR Decomposition
Get PDFA novel method is proposed for solving an EFG-type Saddle-Point (EFG-SP) problem. Although the null-space method and the variable-reduction method (VRM) were developed as a solver of a saddle-point problem, both methods are extremely time-consuming in solving an EFG-SP problem. This is attributable to the QR decomposition that is indispensable for both methods. For the purpose of resolving this problem, the improved Variable-Reduction Method (iVRM) is formulated without using the QR decomposition. A numerical code has been developed for solving an EFG-SP problem with the iVRM, the VRM and the ICCG method. By means of the code, the performance of the three methods is investigated numerically. The results of computations show that, from the standpoint of convergence property and computational speed, the iVRM is even superior to either of the VRM and the ICCG method.journal articl
Test of 10 kA-Class HTS WISE Conductor in High Magnetic Field Facility
Get PDF0000-0002-3541-6298High-temperature superconducting (HTS) conductor is a feasible candidate to make magnets for the next generation fusion devices because of its higher temperature margins and higher critical current in a high magnetic field in comparison to low-temperature superconducting (LTS) conductors. The recently proposed concept of the HTS-WISE (Wound and Impregnated Stacked Elastic tapes) conductor was studied to clarify its characteristics under certain magnetic fields. The WISE conductor, including 30-stacked REBCO (Rare-Earth Barium Copper Oxide) tapes, was fabricated and energized in a 9-T test facility which produced the condition of magnetic field B = 5 - 8 T and a temperature T = 30 - 50 K. Obtained critical currents (5.4 - 10.8 kA) increased with a decreasing magnetic field and/or temperature under the condition of T > 40 K. The maximum current of 16.9 kA was obtained at T = 30 K, which corresponded to the engineering current density jE = 60 A/mm2. Experimental results showed qualitative agreement with numerical calculations of the critical current. We confirmed the operation of the WISE conductor under a high magnetic field and low temperature.journal articl