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Observation of significant Doppler shift in deuterium-deuterium neutron energy caused by neutral beam injection in the large helical device
No full text0000-0002-0160-0468The compact neutron emission spectrometer (CNES) having a tangential sightline was installed to observe a significant Doppler shift of the neutron energy due to the high-energy tangential neutral beam (NB) injections in the Large Helical Device (LHD) for understanding of the energy distribution of fast-ion. The CNES is based on a 1-inch diameter and 1-inch height EJ301 liquid scintillator coupled with a conventional 1-inch photomultiplier tube. The histogram of the integrated pulse signal (Qtotal) during different NBs heating phases measured by the CNES shows that the edge of Qtotal changes depending on NB directions. Using the simple derivative unfolding technique, the neutron energy spectra were unfolded from the measured Qtotal histogram. Peaks of the neutron energy shift to 2.0 MeV, 2.42 MeV, and 3.0 MeV according to the injection direction of NBs. The obtained neutron energy is almost consistent with the virgin deuterium-deuterium neutron energy evaluated by the simple two-body kinematics considering the sightline of CNES, NB injection angle, and NB injection energy.journal articl
Collective Thomson scattering diagnostic with in situ calibration system for velocity space analysis in large helical device
Get PDF0000-0002-2752-3333A collective Thomson scattering (CTS) diagnostic with a ±3 GHz band around a 77 GHz gyrotron probe beam was developed to measure the velocity distribution of bulk and fast ions in high-temperature plasmas. We propose a new in situ calibration method for a CTS diagnostic system combined with a raytracing code. The method is applied in two situations for electron cyclotron emission in plasmas and in a CTS diagnostic with a modulated probe beam. Experimental results highlight the importance of refraction correction in probe and receive beams. The CTS spectrum is measured with the in situ calibrated CTS receiver and responds to fast ions originating from a tangential neutral beam with an energy of 170 keV and from a perpendicular beam with an energy of 60 keV, both in the large helical device. From a velocity space analysis model, the results elucidate the measured anisotropic CTS spectrum caused by fast ions. The calibration methods and analyses demonstrated here are essential for CTS, millimeter-wave diagnostics, and electron cyclotron heating required under fusion reactor conditions.journal articl
小特集：先進燃料核融合研究の現状と展開 ２．先進燃料核融合プラズマ及びその核燃焼
Get PDF0000-0002-7498-4191先進燃料プラズマとして従来検討が進められてきたcat-D，scat-D，DD3He，D3He プラズマ，及びDT プラ
ズマについて，簡単な炉心パワーバランス解析を介した比較を通して特徴を概説する．先進燃料プラズマ中で特
に重要となる，（１）燃料イオン速度分布関数のマックスウェル分布からの歪みとその核融合反応率係数への影響，
（２）高速イオン挙動やイオン加熱に対する核弾性散乱効果を例示する．先進燃料プラズマ研究は，核融合燃料制
御・燃料サイクルの研究に直結する．先進燃燃料プラズマ研究を通した稀少核融合燃料である3He，T の消費・供
給バランス研究の一面を紹介する．journal articl
Development of off-axis spiral phase mirrors for generating optical vortices in a range of millimeter waves
Get PDF0000-0002-2983-5920In this paper, we report the development of off-axis spiral phase mirrors that can be used to generate optical vortices from a range of millimeter waves. An obliquely incident Gaussian beam is reflected from a spiral phase mirror and is converted into an optical vortex beam with a desired topological charge. The mirrors were fabricated by mechanical machining. The designed vortex properties of reflected waves were investigated experimentally by using a low-power test, where the designed topological charge was verified based on the interference pattern between a vortex beam and a Gaussian-like beam. The designed topological charge was also estimated by using a phase retrieval method specialized for a vortex beam. These off-axis spiral phase mirrors can be used for propagation experiments of radio frequency waves with helical wavefronts in magnetized plasma.journal articl
Cyogenic Thermal Conductivity Measurements of Yb:YAG Ceramics
Get PDF0000-0002-9217-8812Thermal conductivity of 9.8 at% Ytterbium-doped Yttrium Aluminum Garnet (Yb:YAG) ceramics has been measured by three systems at Commissariat à l'Énergie Atomique et aux énergies alternatives (CEA Paris-Saclay) and at the National Institute for Fusion Science (NIFS). For accurate measurements, thermal impedances in thermal systems should be negligibly small. However, each system includes some thermal impedance in a heat flow path. This paper describes that thermal conductivity of the 9.8% doped Yb:YAG ceramics and discusses the compensation method for thermal impedance in each system.journal articl
Prediction of the energetic particle redistribution by an improved critical gradient model and analysis of the transport threshold
Get PDF0000-0003-3311-5931Based on the theory of critical gradient model (CGM) and following the simulation method proposed by Waltz et al. [Nucl. Fusion 55, 123012 (2015)], a combination of TGLFEP and EPtran code is employed to predict the energetic particle (EP) transport induced by Alfvén eigenmodes (AEs). To be consistent with the experiment, recent improvements to the simulation method include consideration of threshold evolution and orbit loss due to finite orbit width. The revised CGM is applied to simulate two DIII-D experimental discharges (#142111 and #153071). It well reproduces the experimental profiles with multiple unstable AEs and large-scale EP transport. Discharge #142111 had previously been simulated using a nonlinear MHD-kinetic code MEGA [Todo et al., Nucl. Fusion 55, 073020 (2015)] with a transport mechanism based on stochasticity induced by overlapping AE. By comparing the simulated EP profiles, we find that the AE transport threshold is approximated by both the MEGA nonlinear stability threshold and the proposed CGM threshold (error <5% for single n and <17% for multiple n simulation). Both of them are larger than the linear stability threshold of the most unstable AE mode by a quantity of the order of the flux needed to sustain EP transport by the background turbulence. We have also applied the improved CGM to simulate the α particle redistribution for a China Fusion Engineering Test Reactor steady state scenario. Because of the clear separation between the AE unstable region and the loss cone, only a moderate α particle loss of ∼9.6% is predicted.journal articl
Electromagnetic-Structural Analysis of a Superconducting Magnet With Active Shielding for a Rotating Gantry
Get PDF0000-0002-1989-867XAs a magnet utilized for a rotating gantry in heavy particle radiotherapy, a superconducting magnet with active shielding has been proposed to reduce the magnet weight. The magnet is composed of a dipole coil and an active shielding coil wound with NbTi wires. In this study, an electromagnetic-structural analysis of the magnet with active shielding was conducted using an FEM model. The results of the analysis indicate that the coil deformation, due to an electromagnetic force, slightly affects the field quality but negligible for the operation. The design concept of superconducting magnets with active shielding is valid in terms of magnetic field and the support structure for a rotating gantry. In addition, based on the previous study, the weight of the superconducting magnet with active shielding was revaluated. As a result, the superconducting magnet with active shielding can be one-third lighter than a superconducting magnet surrounded with an iron yoke, in terms of the magnet weight per unit length.journal articl
Simulation of Non-Uniform Current Distribution in Stacked HTS Tapes
Get PDF0000-0002-0687-7191Low-Temperature Superconductors (LTS) are sensitive to non-uniform current distribution, which produces quenching. So, transposition of strands is indispensable in LTS cables to help current redistribution. In contrast, High-Temperature Superconductors (HTS) have higher thermal stability, which is expected to help current redistribution among strands (tapes) without quenching. Generally, HTS cable designs consider transposition to reduce quench likelihood and better handling AC operation. However, transposition causes mechanical strain in the tapes, reducing their performance. Recently, a 20-kA-class Stacked Tapes Assembled in Rigid Structure (STARS) conductor is being developed at NIFS, for the next-generation helical devices. To weigh the simple stacking feasibility of HTS tapes, a previous experiment confirmed, that 5 non-transposed HTS tapes can stably conduct a worst-case non-uniform current distribution without quenching. This further suggests that when using HTS tapes for DC HTS cables, transposition may be optional, but not strictly required. A numerical simulation was developed, dealing with the current distribution among the HTS tapes in a worst-case scenario, reproducing the previous experimental observation, and a second experiment was performed to give insights into the contact resistance between HTS tapes. The self-magnetic field effect and temperature fluctuations are to be explored for quench scenarios.journal articl
Gyrokinetic Turbulent Transport Simulations on Steady Burning Condition in D-T-He Plasmas
Get PDF0000-0003-2693-4859Ion temperature gradient (ITG) and trapped electron modes (TEM) driven turbulent transport in an ITER-like plasma is investigated by means of multi-species gyrokinetic Vlasov simulations with D, T, He, and real-mass kinetic electrons including their inter-species collisions. Beyond the conventional zero-dimensional power balance analysis presuming the global energy and particle confinement times, gyrokinetic-simulation-based evaluation of a steady burning condition with He-ash exhaust and D-T fuel inward pinch is demonstrated. It is clarified that a significant imbalance appears in the turbulent particle flux for the fuel ions of D and T, depending on the D-T density ratio and the He-ash accumulation. Then several profile regimes to satisfy Reiter's steady burning condition are, for the first time, identified by the gyrokinetic simulation. Also, the impacts of zonal flows and nonthermal He-ash on the optimal profile regimes are examined.journal articl