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Rotating magnetization method for inspection of local defect in HTS conductor
No full textHigh temperature superconducting (HTS) magnet used for a accelerator for high energy physics or a large-scale magnetic confinement system for nuclear fusion requires large current capacity HTS conductor in order to dump the stored magnetic energy quickly to protect the coil when quench has been occurred. To realize the HTS conductor, superimposed or stacked HTS tapes conductors are invented. However, local degradation of the critical current has been observed in the production of HTS conductors. Therefore, to confirm the soundness of the HTS conductor, it is necessary to establish the non-destructive detection method for the observation of degraded HTS tapes. In this study, we have investigated to inspect the degradation position in stacked HTS tapes by adopting rotating magnetization measurement method. This measurement method is measuring magnetization signal by rotating and transporting stacked HTS tapes in a static magnetic field. As a result, intentionally introduced buckling defect positions were detected by this measurement method.journal articl
Upgrading LHDGauss Code by Including Obliquely Propagating Wave Absorption Effect for ECH
Get PDF0000-0002-4501-1956LHDGauss is a multi-ray tracing code to calculate microwave beam propagation and power deposition of electron cyclotron heating (ECH) using the electron density and electron temperature profiles in the Large Helical Device (LHD) plasma. LHDGauss also takes into account the injected wave polarization purity. LHDGauss uses the cold plasma dispersion to calculate ray propagation and derives the power absorption profile of ECH by using the absorption coefficient based on weakly relativistic plasmas and the wave propagating perpendicularly to the magnetic field. However, the ECH beam propagation is mainly oblique to the magnetic field in the LHD and it is necessary to take into account the angular dependence of the absorption coefficient in order to derive more accurate ECH power deposition profiles. We upgraded LHDGauss and were able to calculate the absorption coefficient using the weakly relativistic dielectric tensor which considers the influence of the angle between the magnetic field and the wave vector. We compared the power deposition profiles calculated by previous and upgraded LHDGauss with the changes of the electron temperature profile of the LHD plasma in the oblique and the perpendicular O1-mode ECH injection cases. We have obtained more reasonable power deposition profiles by using the upgraded LHDGauss in both the perpendicular and the oblique injection cases.journal articl
Neutron energy spectrum measurement using CLYC7-based compact neutron emission spectrometer in the Large Helical Device
Get PDF0000-0002-0160-0468angential compact neutron emission spectrometer (CNES) based on the Cs2LiYCl6:Ce with 7Li-enrichment (CLYC7) scintillator is newly installed in the Large Helical Device (LHD). Measurement of neutron energy spectrum was performed using CNES in tangential neutral beam (NB) heated deuterium plasma discharges. The Doppler shift of neutron energy according to the direction of tangential NB injection has been obtained. When the fast ions moving away from the CNES, lower shifted neutron energy is obtained, whereas the upper shifted neutron energy is obtained when the fast ions moving toward the CNES. The obtained neutron energy is almost consistent with the virgin deuterium-deuterium neutron energy evaluated by the simple two-body kinematic calculation.journal articl
Neutron and gamma-ray transport calculations in support of the design of the radiation shielding for the TOFED neutron spectrometer at LHD
Get PDFThe neutron emission spectrometer (NES) has been commissioned at the Large Helical Device (LHD) with a new Time-Of-Flight-Enhanced-Diagnostics (TOFED). The aim of the TOFED is to measure the neutron energy spectrum to study the fast-ions behavior such as high-energy ions created by ion cyclotron resonance heating, beam ions, and D-D fusion born 1 MeV tritons in LHD. The instrument is assembled of the first detector S1 and the second detector S2. In 2019, TOFED was installed at Z = 13.5 m below midplane without the radiation shielding and was initially commissioned. Due to neutrons streaming through a considerable number of holes in the LHD torus hall, the ambient background radiation at the TOFED was higher than expected, which causes the large number of coincidental events on the detectors. The obtained time difference between S1 and S2 provides the strong suggestion of TOFED relocation and of TOFED shielding development. In 2020, TOFED was relocated to the basement at Z = 18.5 m below midplane. In this work, a dedicated radiation shielding design is investigated using the Monte Carlo N-Particle code (MCNP6). The shielding design fulfills the design criteria on the radiation moderation capability and engineering constraints. Due to the design criteria, borated polyethylene with thickness of 20 cm is being considered as a neutron shielding and lead with thickness of 5 cm is being considered as a gamma-ray shielding. The shielding is suggested to be a rectangular polyhedron shaped roof. With the designed shielding, neutron flux is reduced by approximately two orders of magnitude at S1 and by approximately more than two orders of magnitude at S2 while prompt gamma-ray fluence is reduced by approximately two orders of magnitude. Here, the detailed design of radiations shielding for the TOFED at LHD is presented. The appropriate radiation shielding from this work will be installed at TOFED.journal articl
Prediction of unusual plasma discharge by using Support Vector Machine
Get PDFThis paper proposes a method for predicting an unusual emission of visible light inside the plasma vessel by using a Support Vector Machine (SVM) because the unusual emission of visible light can be caused by unexpected heating on the vessel surface. This emission must be predicted to avoid unexpected situations in which it causes some damage to the vessel. The light reflected from the divertor tiles is used as the unusual emission light. This study aims to predict such unusual emission through pictures before the start of the unusual emission, regardless of the plasma physics. This study experimentally confirms that the unusual emission of visible light inside the plasma vessel can be predicted with an accuracy rate of 96.4%, and approximately 0.3 s before the start of an unusual emission.journal articl
Effects of core stochastization on particle and momentum transport
Get PDF0000-0003-3646-5427The effects of the stochastic magnetic field in a plasma center produced by electron cyclotron current drive (ECCD) on transport have been revealed. Because the electron temperature profile is flat in the core region, in the case of counter-directed ECCD (ctr-ECCD) against the toroidal magnetic field, the magnetic field is stochastic in the core region with rotational transform ᵼ ∼ 1/3. The particle diffusion coefficient of the ctr-ECCD plasma is approximately 20 times as large as that of the plasma without the stochastic magnetic field produced by co-directed ECCD (co-ECCD) at the maximum. Furthermore, in the stochastic magnetic field with ctr-ECCD, counter-directed intrinsic rotation is observed in the plasma with balanced NBI discharge.journal articl
Coherent cyclotron emission with a helical wavefront from multi-electron system accelerated by the circularly polarized wave
Get PDF0000-0001-6636-8500In this paper, we calculated the radiation from the state where an electron in cyclotron motion under the uniform magnetic field Bex was accelerated by the externally applied circularly polarized wave with strong Ein and Bin. The electron was accelerated in the parallel direction by the term β⊥ × Bin (β⊥: perpendicular velocity of the electron) as well as in the perpendicular direction by the electric field of the wave Ein. Then, the electron can be resonantly accelerated when the Bex is set to the magnetic field strength which is equivalent to frequency of the externally applied circularly polarized wave. The radiation from such an accelerated electron was confirmed to have helical wavefront at harmonics cyclotron frequency.journal articl
A New Wide-area Monitoring System of Electromagnetic Fields around Megawatt-class Amplifiers for Ion Cyclotron Range of Frequency Heating at a Fusion Test Facility
Get PDFNuclear fusion research requires the production of high-temperature plasma. One of the plasma heating methods is the use of radio frequency (RF) waves. The RF wave heating system uses a high-power amplifier, which poses a concern about the leakage electromagnetic fields. Therefore, a new wide-area multipoint electromagnetic monitoring system using personal RF monitors has been developed. The developed monitoring system was applied to the megawatt-class amplifiers for the “ion cyclotron range of frequency” (ICRF) heating system in the frequency range of ion cyclotron resonance from 30 to 40 MHz. As a result, the leakage magnetic field was less than the measurement sensitivity during the plasma experiment, in which the leakage electric field was detected with sufficient sensitivity. The leakage electric field becomes larger as the RF forward power increases, and thus the electric field would be radiated through the stub and/or high voltage supply line connected to the anode of tetrode in the ICRF amplifier. The electric field around the ICRF amplifiers did not exceed the reference level of International Commission on Non-Ionizing Radiation Protection (ICNIRP). The developed wide-area multipoint monitoring system will be useful for monitoring the leakage RF electromagnetic fields around the ICRF heating system at the future fusion devices.journal articl
Effect of tantalum addition on the tensile properties of V-Ta-4Cr-4Ti quaternary alloys
Get PDF0000-0001-6564-8922Various V-Ta-4Cr-4Ti quaternary alloys containing different amounts of Ta were investigated to determine the effect of Ta concentration on their tensile properties. Six button-shaped ingots of V-xTa-4Cr-4Ti alloys (x = 4, 8, 15, 22, 24, and 35 wt.%) were fabricated on a laboratory scale by using non-consumable arc-melting in argon atmosphere. The sheet specimens for all the V-Ta-4Cr-4Ti alloys examined herein were obtained by cold-rolling; hot-rolling or intermediate annealing was not required. Although the examined alloys were fabricated on a laboratory scale, the high-Ta alloys, unlike the high-Cr alloys, did not experience crack formation in the cold rolling process. It is possible that V-4Cr-4Ti alloys adopt large amount of Ta and its strengthening effect without negative impact on rolling fabricability. Tensile strength tended to increase with increasing Ta content at both room temperature and high temperatures of 973 K and 1073 K, which can be attributed to the solid solution strengthening by Ta. Thus, addition of Ta to V-4Cr-4Ti alloys can improve their strength without decreasing their rolling fabricabilities. However, an alloy containing excess Ta (V-35Ta-4Cr-4Ti) showed a loss of ductility and a brittle fracture mode due to the formation of a large amount of friable Laves phase. Therefore, it is necessary to limit the amount of Ta to prevent the formation of the Laves phase.journal articl
Effects of Toroidally Distributed Divertor Biasing on Scrape-Off-Layer Plasma in the QUEST Spherical Tokamak
Get PDF0000-0002-8244-8305A novel divertor biasing using four biasing plates that are arranged toroidally every 90° on the upper divertor plate is applied to low-density plasmas of the QUEST spherical tokamak. When some of these plates are biased in-phase by applying a sawtooth waveform voltage of 85-V amplitude and 50-Hz repetition, up to approximately 35% reduction of the particle flux to the divertor is observed during positive biasing. The input power for the flux reduction is approximately 0.2 kW for low-density tokamak plasmas produced by ∼130-kW electron cyclotron wave injection. Additionally, the signal of a plate probe placed in the low-field side of the mid-plane of the vacuum vessel indicates enhanced losses of fast electrons during positive biasing. The enhanced loss is attributed to small resonant magnetic perturbations produced by the bias-driven currents in the scrape-off layer. This novel divertor biasing is expected to provide a new experimental tool for studying divertor heat load control and fast electron confinement in a tokamak device.journal articl