Thermal neutron flux evaluation by a single crystal CVD diamond detector in LHD deuterium experiment

The single crystal CVD diamond detector (SDD) was installed in the torus hall of the Large Helical Device (LHD) to measure neutrons with high time resolution and neutron energy resolution. The LiF foil with 95.62 % of 6Li isotope enrichment pasted on the detector was used as the thermal neutron convertor as the energetic ions of 2.0 MeV alpha and 2.7 MeV triton particles generated in LiF foil and deposited the energy into SDD. SDD were exposed to the neutron field in the torus hall of the LHD during the 2nd campaign of the deuterium experiment. The total pulse height in SDD was linearly propotional to the neutron yield in a plasma operation in LHD over 4 orders of magnitude. The energetic alpha and triton were separately measured by SDD with LiF with the thickness of 1.9 μm, although SDD with LiF with the thickness of 350 μm showed a broadened peak due to the large energy loss of energetic particles generated in the bulk of LiF. The modeling with MCNP and PHITS codes well interpreted the pulse height spectra for SDD with LiF with different thicknesses. The results above demonstrated the sufficient time resolution and energy discrimination of SDD used in this work

Femoral neck fracture with osteoporosis in Tokushima Prefecture

The numbers and features of occurrence, causes, treatments and prognosis of femoral neck fracture with osteoporosis in Tokushima prefecture were investigated in the 10th fiscal year of Heisei. 634 patients (154 males and 480 females) suffered from the femoral neck fracture. Females were 3.1 times as many as males. In females, the occurrence of the fracture had a tendency to increase to 85-years-old population. In fracture types, 253 cases were intracapsular type and 381 cases extracapsular type. Extracapsular type of the femoral neck fracture increased in proportion to aging. 384 cases were treated with osteosynthesis, 207 cases with femoral prosthesis and 43 cases with othermethods. The main cause of the fracture was trivial fall (79%). 288 cases returned to home and 258 cases still admitted in the secondary hospitals. 69 cases entered to the nursing home. Half of the patients who could walk with or without crutch before fracture were able to return to home, on the other hand, the ratio of patients who could return to home among the patients with no ability of walk before injury was less than 10%. Mortality rate was 2.1 % at the discharge

Magnetic configuration effects on TAE-induced losses and a comparison with the orbit-following model in the Large Helical Device

Fast-ion losses from Large Helical Device (LHD) plasmas due to toroidal Alfvén eigenmodes (TAEs) were measured by a scintillator-based lost fast-ion probe (SLIP) to understand the loss processes. TAE-induced losses measured by the SLIP appeared in energy E ranges of around 50–180 keV with pitch angles χ between 35°–45°, and increased with the increase in TAE amplitudes. Position shifts of the magnetic axis due to a finite plasma pressure led not only to an increase in TAE-induced losses but also to a stronger scaling of fast-ion losses on TAE amplitudes. Characteristics of the observed fast-ion losses were compared with a numerical simulation based on orbit-following models in which the TAE fluctuations are taken into account. The calculation indicated that the number of lost fast ions reaching the SLIP increased with the increase in the TAE amplitude at the TAE gap. Moreover, the calculated dependence of fast-ion loss fluxes on the fluctuation amplitude became stronger in the case of large magnetic axis shifts, compared with the case of smaller shifts, as was observed in the experiments. The simulation results agreed qualitatively with the experimental observations in the LHD

Development of Faraday-cup-based Fast Ion Loss Detector in Wendelstein 7-X

A study on fast-ion losses due to magnetic field ripples and fast-ion-drivenmagnetohydrodynamic (MHD) modes is important in terms of view of research on fusion-born alpha losses in fusion devices. To understand fast-ion loss in Wendelstein 7-X (W7-X) plasmas, installation of fast-ion loss diagnostics for W7-X has been planned. For the Op1.2b campaign, the prototype Faraday-cup-based fast-ion loss detector (FILD) has been designed as joint cooperative project between National Institute for Fusion Science and Max Planck Institute for Plasma Physics. The Faraday-cup-based FILD is relatively cost-effective in construction compared with a scintillator-type FILD. The FILD is capable of providing the flux, pitch angle, and Larmor radius of escaping fast ions simultaneously, providing the clear understanding on fast-ion losses induced by MHD mode as well as non-axisymmetric magnetic field ripples.A Lorentz orbit code (LORBIT code and ASCOT code) has been used to find a position suitable for detection of escaping beam ions. It is found that the sufficient beam-ion flux on the head position of the multi-purpose manipulator (MPM) is expected. Therefore, we decided to install the prototype FILD head using the MPM. The detector is mainly composed of a molybdenum head having a set of two apertures restrict the orbits of fast ions that can enter the probe and eight Faraday films as a charge collector. The size and the position of thoseapertures are decided using the grid calculation program. Faraday film is a thin film of aluminum vapor deposited onto one side of the quartz substrate. The thickness of the films is approximately 0.2 μm. Electric current from each Faraday film will be carried to the low input impedance current amplifier (I-76, NF Corporation) and an isolation amplifier. The signal level of the FILD predicted by the ASCOT code is up to 0.5 μA, which is comparable with that of a FILD in the Compact Helical System (CHS)

Energetic ion losses caused by magnetohydrodynamic activity resonant and non-resonant with energetic ions in Large Helical Device

Experiments to reveal energetic ion dynamics associated with magnetohydrodynamic activity are ongoing in the Large Helical Device (LHD). Interactions between beam-driven toroidal Alfvén eigenmodes (TAEs) and energetic ions have been investigated. Energetic ion losses induced by beam-driven burst TAEs have been observed using a scintillator-based lost fast-ion probe (SLIP) in neutral beam-heated high β plasmas. The loss flux of co-going beam ions increases as the TAE amplitude increases. In addition to this, the expulsion of beam ions associated with edge-localized modes (ELMs) has been also recognized in LHD. The SLIP has indicated that beam ions having co-going and barely co-going orbits are affected by ELMs. The relation between ELM amplitude and ELM-induced loss has a dispersed structure. To understand the energetic ion loss process, a numerical simulation based on an orbit-following model, DELTA5D, that incorporates magnetic fluctuations is performed. The calculation result shows that energetic ions confined in the interior region are lost due to TAE instability, with a diffusive process characterizing their loss. For the ELM, energetic ions existing near the confinement/loss boundary are lost through a convective process. We found that the ELM-induced loss flux measured by SLIP changes with the ELM phase. This relation between the ELM amplitude and measured ELM-induced loss results in a more dispersed loss structure

A study on the TAE-induced fast-ion loss process in LHD

Characteristics of fast-ion losses induced by toroidal-Alfv en eigenmodes (TAEs) are investigated over wide parameter ranges of Large Helical Device (LHD) plasmas to reveal the fast-ion loss process. To study fast-ion losses, a scintillator-based lost-fast ion probe is used, and an increment of fast-ion loss flux due to TAEs from the neoclassical orbit loss level (ΔΓfast ion) is measured. The dependence of ΔΓfast ion on the TAE magnetic fluctuation amplitude(bθTAE) changes from a linear to a quadratic and finally a third power with an increase in the magnetic axis shift. It is found that the dependence of fast-ion loss flux on TAE magnetic fluctuation amplitudes changes at a certainfluctuation level in a fixed configuration. Experimental results show that in the small bθTAE regime, ΔΓfast ion is proportional to bθTAE, whereas ΔΓfast ion increases with the square of bθTAE in the larger bθTAE regime. A simulationby orbit-following codes that incorporate magnetic fluctuations with frequency chirping-down due to TAEs suggests the change in the fast-ion loss process from a convective ( ΔΓ ion ∝ bθTAE) to a diffusive (ΔΓfast ion ∝ b2 θTAE) character as bθTAE increases

Laser-driven multi-MeV high-purity proton acceleration via anisotropic ambipolar expansion of micron-scale hydrogen clusters

強力なレーザーを使ってエネルギーがそろった純度100％の陽子ビーム発生に成功 --レーザー駆動陽子ビーム加速器の実現へ向けて大きく前進--. 京都大学プレスリリース. 2022-10-13.Multi-MeV high-purity proton acceleration by using a hydrogen cluster target irradiated with repetitive, relativistic intensity laser pulses has been demonstrated. Statistical analysis of hundreds of data sets highlights the existence of markedly high energy protons produced from the laser-irradiated clusters with micron-scale diameters. The spatial distribution of the accelerated protons is found to be anisotropic, where the higher energy protons are preferentially accelerated along the laser propagation direction due to the relativistic effect. These features are supported by three-dimensional (3D) particle-in-cell (PIC) simulations, which show that directional, higher energy protons are generated via the anisotropic ambipolar expansion of the micron-scale clusters. The number of protons accelerating along the laser propagation direction is found to be as high as 1.6 ±0.3 × 10⁹/MeV/sr/shot with an energy of 2.8 ±1.9 MeV, indicating that laser-driven proton acceleration using the micron-scale hydrogen clusters is promising as a compact, repetitive, multi-MeV high-purity proton source for various applications

Observation of energetic-ion losses induced by various MHD instabilities in the Large Helical Device (LHD)

Energetic-ion losses induced by toroidicity-induced Alfvén eigenmodes (TAEs) and resistive interchange modes (RICs) were observed in neutral-beam heated plasmas of the Large Helical Device (LHD) at a relatively low toroidal magnetic field level (⩽0.75 T). The energy and pitch angle of the lost ions are detected using a scintillator-based lost-fast ion probe. Each instability increases the lost ions having a certain energy/pitch angle. TAE bursts preferentially induce energetic beam ions in co-passing orbits having energy from the injection energy E = 190 keV down to 130 keV, while RICs expel energetic ions of E = 190 keV down to ∼130 keV in passing–toroidally trapped boundary orbits. Loss fluxes induced by these instabilities increase with different dependences on the magnetic fluctuation amplitude: nonlinear and linear dependences for TAEs and RICs, respectively

Indirect energy transfer channel between fast ions via nuclear elastic scattering observed on the large helical device

An energy transfer phenomenon between energetic ions, which cannot be explained only considering the Coulomb scattering process, was observed on a large helical device (LHD). This phenomenon often occurs in fusion reactivity enhancement and fast-ion slowing-down process that can be observed as a delay in the decay time of the D(d,n)3He neutron generation rate. The transferred energy required to induce such a reactivity enhancement or delay in the fast-ion slowing-down time (neutron decay time) was examined based on the Boltzmann−Fokker−Planck analysis in which a discrete energy transfer process, called nuclear elastic scattering (NES), is included. It was shown that even though the cross section of the NES is smaller than that of the Coulomb scattering, enough knock-on population appears in the energetic region in ion distribution function to induce the observable NES effects; thus, enough energy is transferred from beam ions to fast component of bulk ion distribution function indirectly and the transferred energy per unit time via NES is comparable to the Coulomb scattering rate. This study analytically demonstrates that the observed phenomena on LHD can be explained smoothly by considering the alternative indirect energy transfer channel between energetic ions, which can be comparable with the one via Coulomb scattering