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Stable operation characteristics and perspectives of the large-current HTS STARS conductor
Get PDFORCID 0000-0002-4489-8241The High-Temperature Superconducting (HTS) magnet option has been explored for fusion reactors as well as for next-generation fusion experimental devices. The Stacked Tapes Assembled in Rigid Structure (STARS) conductor uses HTS tapes with simple stacking without twisting and transposition. A practically applicable STARS conductor is presently being developed with an operating current of 18 kA at 20 K temperature and ~15 T magnetic field. The conductor is required to have a high current density of 80 A/mm2. For the second stage of the conductor development, internal electrical insulation is applied between the copper stabilizer casing and the outer stainless-steel jacket, and a 6-m conductor sample was fabricated in a solenoid coil shape with a 600-mm diameter and three turns. The coiled sample was tested in 8 T, 20 K using a facility equipped with a maximum 13-T, 700-mm bore solenoid coil. Excitation up to the rated current of 18 kA was successfully attained with stable operation. The characteristics of the conductor observed during the excitation test are discussed.journal articl
Fast-sampling fast-ion D-alpha measurement using multi-anode photomultiplier tube in large helical device
Get PDFORCID 0000-0002-5222-6082A fast-sampling fast-ion D-alpha (F-FIDA) measurement has been developed in the large helical device in order to investigate fast ion dynamics associated with helically trapped fast-ion-driven Magnetohydrodynamic (MHD) bursts. F-FIDA consists of a multi-anode photomultiplier tube (PMT) and achieves a sampling rate of 10 kHz. During the deuterium experiment campaign in 2022, F-FIDA measured the spectrum of perpendicular fast ions, using perpendicular lines of sight. We compared F-FIDA with conventional FIDA, using an electron multiplying charge coupled device, and confirmed that the time-averaged images were generally consistent between the two. The statistical properties of the temporal evolution associated with MHD bursts were analyzed using a conditional sampling technique. The results showed that the PMT signal varied in different spatial and wavelength channels. Although the signal-to-noise ratio was poor and there was room for improvement, it could provide useful information for studies on the phase-space dynamics of fast ions.journal articl
Tungsten nanostructure growth by sputtering and redeposition in BCA-MD-KMC hybrid simulation
Get PDFORCID 0000-0003-2345-0146The formation mechanism of fibrous tungsten nanostructures, fuzz, induced by helium plasma irradiation on tungsten materials has been investigated. We have developed a BCA-MD-KMC hybrid simulation, which solves the injection process of helium atoms by the Binary Collision Approximation (BCA) method, the diffusion process of helium atoms in tungsten materials by the Kinetic Monte-Carlo (KMC) method, and the deformation of tungsten materials due to helium bubbles by the Molecular Dynamics (MD) method. In addition, the model used to calculate the recoiling of tungsten atoms in BCA was improved to account for the reduced binding energy of tungsten atoms on rough surfaces. Using the hybrid simulation, the height of the nanostructures reached about 50 nm. The main mechanism of nanostructure growth was that sputtering and redeposition caused transport of tungsten atoms perpendicular to the surface. The present simulation was able to represent not only the dependence that the nanostructure height increases in proportion to the square root of the helium fluence, but also the existence of incubation fluence before the growth starts.journal articl
Theory and simulations of field strengths in magnetosonic shock waves in finite beta plasmas
Get PDF0000-0003-2691-5068Field strengths in an oblique magnetosonic shock wave in a collisionless, finite beta plasma are studied with theory and simulations. With the use of the warm, two-fluid model, the maximum values of the magnetic field, the transverse electric field, and the electric potential in a shock wave are analytically obtained as functions of the shock speed. One-dimensional, electromagnetic particle simulations are then carried out to measure the field strengths in shock waves. The theory and the simulation results are found to be consistent.journal articl
Spatial Profiles of NeVI-NeX Emission in ECR-Heated Discharges of the Large Helical Device with Divertor Detachment Induced by RMP Application and Ne Impurity Seeding
Get PDF0000-0002-1171-8603In the Large Helical Device, the divertor detachment has been attempted by application of resonant magnetic perturbation (RMP) field and Ne gas puffing in electron cyclotron resonance- heated discharges for compatibility of high central electron temperature and low divertor heat load. Two kinds of divertor detachment phases were observed. The first one appeared transiently just after the Ne gas puffing (1st detachment), and the second one appeared steadily in the latter half of the discharge (2nd detachment). Space-resolved extreme ultraviolet spectroscopy revealed that NeVI-NeVIII emissions increased slightly outside the last closed flux surface (LCFS), while NeIX and NeX emissions increased inside the LCFS in the 1st detachment phase. Although in the 1st detachment the divertor heat load was significantly reduced, the central electron temperature also decreased because the Ne ions were penetrated inside the LCFS as a radiation source. In the 2nd detachment phase, NeVI-NeVIII emissions increased outside the LCFS while NeIX and NeX emissions kept low intensity inside the LCFS. In this phase, low divertor heat load and high central electron temperature were obtained simultaneously because the Ne ions were localized outside the LCFS as a radiation source. The profile measurements of Ne emission show that the edge island structure created by the RMP application impacts on the impurity emission distribution, where the peak of the emission shifts radially stepwise as the detachment proceeds.journal articl
小特集：先進燃料核融合研究の現状と展開 ３．D-3He，D-D 先進燃料核融合炉の探究
Get PDF0000-0002-6111-6790より安全なD-3He，D-D 先進燃料核融合炉の実現可能性について概説する．高アスペクト比のトカマクでは
ベータ値が低いので自己点火は困難であるが，ベータ値を高くとれる球状トカマク（Spherical tokamak，ST）で
は自己点火が可能なことを示す．しかしこれらの炉のプラズマ電流は１００MA 程度と大きく，ディスラプションが
大きな問題である．そこでディスラプションを起こさずにすみそうな逆転磁場ピンチ（reversed-field pinch，
RFP）を用いてD-３He 炉ができないかも考える．さらにプロトン・ボロン（p-B）炉についても議論し，これらの
先進炉にまつわる様々な問題点，その研究の魅力についても触れる．journal articl
Non-local transport nature revealed by the research in transient phenomena of toroidal plasma
Get PDF0000-0002-0585-4561The non-local transport nature revealed by the research in transient phenomena of toroidal plasma is reviewed. The following non-local phenomena are described: core temperature rise in the cold pulse, hysteresis gradient–flux relation in the modulation ECH experiment, and see-saw phenomena at the internal transport barrier (ITB) formation. There are two mechanisms for the non-local transport which cause non-local phenomena. One is the radial propagation of gradient and turbulence. The other is a mediator of radial coupling of turbulence such as macro/mesoscale turbulence, MHD instability, and zonal flow. Non-local transport has a substantial impact on structure formations in a steady state. The turbulence spreading into the ITB region, magnetic island, and SOL are discussed.journal articl
Recent Progress of Neutron Spectrometer Development for LHD Deuterium Plasmas
Get PDFThe commissioning of three different types of D-D neutron energy spectrometer has been performed in the Large Helical Device (LHD) to accelerate energetic-ion physics studies in a non-axisymmetric system. Because the LHD is equipped with negative-ion-source-based tangential neutral beam injectors (N-NBs) characterized by high energy up to 180∼190 keV, a significant Doppler shift of D-D neutron energy from 2.45 MeV is expected. Two different compact neutron energy spectrometers, i.e., a conventional liquid organic scintillator, designated as EJ-301, and a newly developed Cs2LiYCl6:Ce with 7Li-enrichment called CLYC7, having tangential sightlines, have shown up- and/or down-shifted D-D neutron energy, as expected according to the direction of N-NB injection. In addition, with the aim of study on a perpendicular energetic ion tail, created by wave heating with ion cyclotron resonance frequency, a neutron energy spectrometer named the Time of Flight Enhanced Diagnostic (TOFED) is being developed. The TOFED is based on a time-of-flight technique and is characterized by high-energy-resolution and a high-counting-rate capability. Commissioning of the TOFED is now ongoing. Recent advances of neutron energy spectrometer development for LHD deuterium plasmas are described.journal articl
Evaluation of Alpha Particle Emission Rate Due to the p-11B Fusion Reaction in the Large Helical Device
Get PDF0000-0003-4555-1837A numerical study of the alpha particle emission rate due to the p-11B fusion reaction based on the respectively obtained Large Helical Device (LHD) plasma parameters in an experiment is performed. First, the total alpha particle emission rate is estimated by employing the beam ion distribution calculation code FIT3D and the fusion reaction rate calculation code FBURN based on the classic confinement of beam ions. Then, the calculation is performed using hydrogen-beam-heated hydrogen plasma parameters and the radial boron density profile obtained from boron drop discharge. The result shows that the total alpha particle emission rate reaches approximately 1014 s−1. Then, based on the radial profile of the alpha particle emission calculated by the FBURN code, the distribution of the first orbit loss of5.78-MeV alpha particles created by the p-11B reaction on the vacuum vessel and the divertor plate is calculated by the collisionless Lorentz orbit code LORBIT. Although most of the alpha particles are lost to the divertor plate, some of the alpha particles are lost on the vacuum vessel. Finally, a feasibility study of alpha particle detection by the existing manipulators and fast ion loss detector position is performed. The number of particles as a function of position shows that a substantial number of alpha particles can be detected. Alpha particles with a pitch angle of ~130 deg can reach manipulator positions. In contrast, particles with pitch angles of ~50 and ~110 deg can reach the fast ion loss detector position. The calculation shows that measurement of alpha particles due to p-11B is thought to be possible using charged particle detectors.journal articl
Results of ITER DMS Pellet Material (Neon) Injection into Large Helical Device
Get PDF0000-0002-6634-2025Cryogenic neon pellets of 3 mm in diameter were injected into neutral beam injection (NBI) heated discharges on the Large Helical Device (LHD). The time response of far infrared (FIR) interferometer has pointed out a relatively slow assimilation of the ablated materials compared to the cases of hydrogen injection. This is consistent with the neutral gas and plasma shielding (NGPS) model prediction, showing that strong line emission inside the ablation cloud limits the cloud temperature and the expansion velocity along the magnetic field line. Measured penetration depths were also compared, being well reproduced by the code prediction when the contribution from 180 keV fast ions produced by tangential NBI is taken into account.journal articl