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Numerical investigation of Fe-doped chalcogenide chirped pulse amplifier
Full text linkWe have theoretically investigated the amplification dynamics in an Fe-doped chalcogenide chirped pulse amplifier based on an effective two-level model. The effects of the extraction-during-pumping technique, pump fluence and seed center wavelength on the output performances are thoroughly analyzed. The simulation results show that the gain narrowing and gain shifting effects are serious during the amplification process, while spectral pre-shaping of the seed pulses and the combination of different Fe-doped crystals can effectively suppress the gain narrowing effect. In particular, with appropriate crystal combination, ultra-broadband amplification can be realized, allowing for the generation of few-cycle mid-infrared laser pulses. The investigations conducted in this paper can provide a guideline for the design of Fe-doped chalcogenide chirped pulse amplifiers.journal articl
Isotope effects in linear and saturated ohmic confinement of TCV tokamak and gyrokinetic validation
Full text linkORCID 0000-0002-1606-3204We investigated isotope effects during the tokamak à configuration variable (TCV) ohmic discharge of a diverted positive triangular shape configuration of deuterium (D) and hydrogen (H) plasmas. The transition from the linear ohmic confinement (LOC) regime to the saturated ohmic confinement (SOC) regime was clearly identified from the shot-by-shot density scan experiments. The transport characteristics were almost identical in the H and D plasmas in the LOC regime, and clear improvements were observed in the heat and particle transports in the D plasma compared with the H plasma in the SOC regime. In the SOC regime, the global energy confinement was higher in the D plasma than in the H plasma. Improvements in the SOC regime were evident in the ion channel of the heat transport and the diffusion term of the particle transport. Intrinsic toroidal rotation was found. Its profiles were identical in the H and D plasma in the LOC regime. However, the steeper gradient of toroidal rotation was found in the D plasma than in the H plasma in the SOC regime. The gyrokinetic modeling of switching ion species and keeping identical input profiles showed no difference of the heat flux in the LOC regime and a clear reduction in the D plasma heat flux in the SOC regime. Additionally, collisionality is shown to play an important role in in the heat flux reduction in D plasmas relative to H plasmas. The gyrokinetic validation of the heat transport against the experimental profiles showed a qualitative agreement regarding the heat and particle fluxes. Quantitative agreement was better for the ion heat channel than for the other transport channels.journal articl
Construction progress of the Chinese First Quasi-axisymmetric Stellarator (CFQS) and preliminary experimental results on the CFQS-Test device
No full textThe Chinese First Quasi-axisymmetric Stellarator (CFQS) is being constructed as an international joint project between Southwest Jiaotong University (China) and the National Institute for Fusion Science (Japan), aiming to prove the inherent advantages of the quasi-axisymmetric (QA) magnetic configuration in confining plasmas. The CFQS project is divided into two stages. The first one focuses on testing the feasibility and accuracy of modular coils for realization of the QA topology, which is conducted on the CFQS-Test (CFQS-T) device and operated at low magnetic field strength of 0.1 T. The second stage is scheduled to delve into plasma properties of high parameters at relatively high magnetic field (1 T) in a QA stellarator. The latter stage will involve installation of dedicated support structures, such as coil cases, central poles and pillars, to withstand the strong electromagnetic force of 1 T operation. By the end of July 2024, the assembly of CFQS-T was completed with a maximum deviation of ∼2.96 mm, meeting the design requirement. Auxiliary systems, including power supply, vacuum pumping, magnetron, central control, water cooling and diagnostic systems, have also been installed and commissioned accordingly. In August 2024, the first QA magnetic configuration was successfully achieved in CFQS-T. This paper outlines the construction progress of CFQS and the preliminary experimental results attained with the CFQS-T device.journal articl
Design and simulation study of scintillation fiber detector for deuterium-tritium fusion neutron measurement on the HL-3 tokamak
No full textIn experimental devices of magnetic confinement fusion with deuterium plasmas, secondary tritons can be exploited to study fast ion physics. This work uses numerical tools to investigate the performance and edge effect of scintillating fiber neutron detectors that enables easy separation of scarce DT neutron signals from gamma signals. Geant4 particle transportation simulations show the relationship of intrinsic detection efficiency and neutron/gamma signal amplitude ratio with four geometrical parameters: fiber length, thickness, distance, and numbers. To understand the fiber edge effect, two simple numerical models concerning recoil protons and gamma induced electrons are established. They can provide good estimation of the detector, consistent with Geant4 simulation results. Two detectors are manufactured based on these results, whose characteristics have been tested by an Am-Be radioactive source.journal articl
Enhancement to gas puffing control system towards precise control of electron density in LHD
No full textA gas puffing system in Large Helical Device (LHD) has been largely enhanced in terms of its functionality. One of the most significant expansions is the enhancement of electron density controllability. In LHD, the precise control of electron density is often required according to the plasma experiment scenario. The electron density is controlled by supplying the appropriate amount of fuel gas through a piezo valve. To improve the performance of electron density control in LHD, we have developed a gas puffing control system (GPCS) including a feedback control system based on proportional-integral-control (PI-control). As a result of applying the PI-control, the target electron density can now be obtained in almost all cases in a single shot. To build the GPCS, a commercial CompactRIO with a field-programmable gate array (FPGA) is newly employed. The GPCS FPGA and the GPCS operating graphical user interface (GUI) are programmed in LabVIEW. This has resulted in easy modification of the GPCS' plasma control performance, and in easy GPCS operation for everyone. The ease of the plasma control performance modification has enabled GPCS to meet a variety of requirements, such as sustaining detachment, in addition to density control.journal articl
Digitalization of Fusion Archive Materials and Development of their Database System
No full textORCID 0000-0001-8170-7531自然科学研究機構 核融合科学研究所 核融合アーカイブ室では，文部科学省のオープンアクセス加速化事業の下，保有する核融合アーカイブ資料のうち約27,000点の電子化作業を行った．また，その画像データおよび目録データ（メタデータ）・管理データを管理・公開するためのアーカイブ資料データベースシステムを構築した．journal articl
Laser spectroscopy of the QED-sensitive transition in Ar14+
Full text linkWe experimentally study the magnetic-dipole 1s22s2p 3P1−3P2 transition in Be-like Ar14+. The
wavelength of this transition is known to be sensitive to the quantum electrodynamics effect and
has been measured many times by emission spectroscopy using an electron beam ion trap (EBIT).
However, there is a significant discrepancy among the previously measured values. Here, we report
the first experimental verification of the transition wavelength by laser spectroscopy. The present
result is 594.5495(21) nm, which is in reasonable agreement (<1.5σ) with the latest value
measured by emission spectroscopy by the Heidelberg EBIT group.journal articl
Kinetic effects of thermal ions on internal kink modes in tokamak plasmas
Full text linkLinear growth of internal kink mode is investigated using a kinetic-MHD hybrid simulation model under realistic tokamak conditions. By comparing purely fluid (single-fluid MHD) simulations with kinetic thermal ion simulations using various coupling schemes, it is demonstrated that thermal-ion effects—including finite orbit width and ion pressure anisotropy—can significantly stabilize the internal kink mode. The maximum perturbation of distribution function aligns with resonance regions and near the passing-trapped boundary, indicating outward transport and redistribution of thermal ions. The net positive energy transfer from the mode to thermal ions leads to a reduction in growth rate. These results underscore the importance of incorporating thermal ion kinetics when modeling internal kink instabilities in fusion plasmas.journal articl
Fiber-in-line infrared spectrometer fabricated by femtosecond laser structuring of microchannels in fluoride glass fiber
Full text linkIn this study, we developed a fiber-in-line infrared spectrometer using fluoride-glass fiber and evaluated its measurement performance. In the fabrication process, a sensor structure functioning as a sample cell for spectroscopic measurements was created in the fiber waveguide by femtosecond laser processing. Measurements of water–glucose samples confirmed the sensor’s ability to obtain transmission spectra, allowing the absorption characteristics of the samples to be determined. The decrease in transmittance at the absorption wavelength of water and glucose confirms the feasibility of an optical fiber in-line infrared absorption spectroscopy measurement system.journal articl
Three-dimensional modelling of plasma structure with generating algorithm of optimal starting points for magnetic field line tracing
Full text linkThe magnetic fields confining plasma in fusion reactors are analyzed using Poincaré plots, which show intersections of magnetic field lines on a poloidal crosssection. Traditional methods for designing vacuum vessels and related structures involve slicing the reactor vertically and analyzing these plots, but this approach is inefficient for understanding plasma shapes globally. Key challenges include the computational cost of magnetic field line tracing and the difficulty in constructing continuous surfaces for the divertor legs due to the limited number of magnetic field lines reaching this area. To address these issues, a new and automatic method has been proposed to increase the number of magnetic field lines constituting the divertor legs by predicting optimal starting points for tracing. The proposed method involves placing starting points on orthogonal lines through the magnetic axis, resulting in a better representation of divertor legs. This new algorithm enhances the efficiency of generating Poincaré plots that depict divertor leg regions more clearly than previous methods. Neural Networks predict voxel data representing the shape of magnetic field lines. Considering the Larmor radius, we calculate an envelope surface that encompasses the region where plasma exists and create 3D modeling data.journal articl