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The gyrokinetic-based turbulent transport models are essential to predict density and temperature profiles, but introducing detailed descriptions of turbulence physics tends to increase the computational cost. To accelerate the profile predictions, a neural-network (NN) based approach has been undertaken. Our study is also developing a NN-based turbulent transport model DeKANIS. A turbulent saturation rule employed in DeKANIS was based on experimental particle fluxes estimated for JT-60U H-mode plasmas, and it was apt to overestimate temperatures. To reduce the overestimation, a different saturation rule is built including experimental heat fluxes.

Ion- and electron-scale microinstabilities and the linear zonal-flow response in mixture plasmas with the medium-Z impurity and He-ash are investigated by means of a multi-species gyrokinetic model. In addition to the charge and dilution effects, stabilization/destabilization by nonthermal He-ash ions is clarified.

準線形乱流輸送モデルDeKANISはニューラルネットワーク(NN)を用いることで、ジャイロ運動論コードが予測する拡散・ピンチ過程の輸送量への寄与を高速に再現できる。NNの学習に用いるデータの拡張などの改良によって、統合コードにおける輸送シミュレーションが可能になった。また、乱流揺動の飽和レベルは半経験的な手法で評価していたが、混合長理論に基づく手法を導入し、汎用性が以前よりも向上する可能性を示した。

Isotope effects are one of the most important issues for predicting future reactor operations. Large helical device (LHD) is the presently working largest stellarator/helical device using super conducting helical coils. In LHD, deuterium experiments started in 2017. Extensive studies regarding isotope effects on transport have been carried out. In this paper, the results of isotope effect studies in LHD are reported. The systematic studies were performed adjusting operational parameters and nondimensional parameters. In L mode like normal confinement plasma, where internal and edge transport barriers are not formed, the scaling of global energy confinement time (τ E) with operational parameters shows positive mass dependence (M 0.27; where M is effective ion mass) in electron cyclotron heating plasma and no mass dependence (M 0.0) in neutral beam injection heating plasma. The non-negative ion mass dependence is anti-gyro-Bohm scaling. The role of the turbulence in isotope effects was also found by turbulence measurements and gyrokinetic simulation. Better accessibility to electron and ion internal transport barrier (ITB) plasma is found in deuterium (D) plasma than in hydrogen (H). Gyro kinetic non-linear simulation shows reduced ion heat flux due to the larger generation of zonal flow in deuterium plasma. Peaked carbon density profile plays a prominent role in reducing ion energy transport in ITB plasma. This is evident only in plasma with deuterium ions. New findings on the mixing and non-mixing states of D and H particle transports are reported. In the mixing state, ion particle diffusivities are higher than electron particle diffusivities and D and H ion density profiles are almost identical. In the non-mixing state, ion particle diffusivity is much lower than electron diffusivity. Deuterium and hydrogen ion profiles are clearly different. Different turbulence structures were found in the mixing and non-mixing states suggesting different turbulence modes play a role.

In recent deuterium experiments on the large helical device (LHD), we succeeded in expanding the temperature domain to higher regions for both electron and ion temperatures. Suppression of the energetic particle driven resistive interchange mode (EIC) by a moderate electron temperature increase is a key technique to extend the high temperature domain of LHD plasmas. We found a clear isotope effect in the formation of the internal transport barrier in high temperature plasmas. A new technique to measure the hydrogen isotope fraction was developed in the LHD in order to investigate the behavior of the isotope mixing state. The technique revealed that the non-mixing and the mixing states of hydrogen isotopes can be realized in plasmas. In deuterium plasmas, we also succeeded in simultaneously realizing the formation of the edge transport barrier (ETB) and the divertor detachment. It is found that resonant magnetic perturbation plays an important role in the simultaneous formation of the ETB and the detachment. Contributions to fusion reactor development from the engineering point of view, i.e. negative-ion based neutral beam injector research and the mass balance study of tritium, are also discussed.

The dynamics in the photosphere is governed by the multi-scale turbulent convection termed as granulation and supergranulation. It is important to derive 3-dimensional velocity vectors to understand the nature of the turbulent convection. However, it is difficult to obtain the velocity component perpendicular to the line-of-sight, which corresponds to the horizontal velocity in disk center observations. We developed a convolutional neural network model with a multi-scale deep learning architecture. The method consists of multiple convolutional kernels with various sizes of the receptive fields, and it performs convolution for spatial and temporal axes. The network is trained with data from three different numerical simulations of turbulent convection, and we introduced a coherence spectrum to assess the horizontal velocity fields that were derived at each spatial scale. The multi-scale deep learning method successfully predicts the horizontal velocities for each convection simulation in terms of the global-correlation-coefficient, which is often used for evaluating the prediction accuracy of the methods. The coherence spectrum reveals the strong dependence of the correlation coefficients on the spatial scales. Although coherence spectra are higher than 0.9 for large-scale structures, they drastically decrease to less than 0.3 for small-scale structures wherein the global-correlation-coefficient indicates a high value of approximately 0.95. We determined that this decrease in the coherence spectrum occurs around the energy injection scales. The accuracy for the small-scale structures is not guaranteed solely by the global-correlation-coefficient. To improve the accuracy in small-scales, it is important to improve the loss function for enhancing the small-scale structures and to utilize other physical quantities related to the non-linear cascade of convective eddies as input data., Comment: 9 pages, 5 figures, accepted for publication in A&A

Recently, the validity range of the approximations commonly used in neoclassical calculation has been reconsidered. One of the primary motivations behind this trend is observation of an impurity hole in LHD (Large Helical Device), i.e. the formation of an extremely hollow density profile of an impurity ion species, such as carbon $\text{C}^{6+}$ , in the plasma core region where a negative radial electric field ( $E_{r}$ ) is expected to exist. Recent studies have shown that the variation of electrostatic potential on the flux surface, $\unicode[STIX]{x1D6F7}_{1}$ , has significant impact on neoclassical impurity transport. Nevertheless, the effect of $\unicode[STIX]{x1D6F7}_{1}$ has been studied with radially local codes and the necessity of global calculation has been suggested. Thus, we have extended a global neoclassical code, FORTEC-3D, to simulate impurity transport in an impurity hole plasma including $\unicode[STIX]{x1D6F7}_{1}$ globally. Independently of the $\unicode[STIX]{x1D6F7}_{1}$ effect, an electron root of the ambipolar condition for the impurity hole plasma has been found by global simulation. Hence, we have considered two different cases, each with a positive (global) and a negative (local) solution of the ambipolar condition, respectively. Our result provides another support that $\unicode[STIX]{x1D6F7}_{1}$ has non-negligible impact on impurity transport. However, for the ion-root case, the radial $\text{C}^{6+}$ flux is driven further inwardly by $\unicode[STIX]{x1D6F7}_{1}$ . For the electron-root case, on the other hand, the radial particle $\text{C}^{6+}$ flux is outwardly enhanced by $\unicode[STIX]{x1D6F7}_{1}$ . These results indicate that how $\unicode[STIX]{x1D6F7}_{1}$ affects the radial particle transport crucially depends on the profile of the ambipolar- $E_{r}$ , which is found to be susceptible to $\unicode[STIX]{x1D6F7}_{1}$ itself and the global effects.

The transition between isotope-mixing and nonmixing states in hydrogen-deuterium mixture plasmas is observed in the isotope (hydrogen and deuterium) mixture plasma in the Large Helical Device. In the nonmixing state, the isotope density ratio profile is nonuniform when the beam fueling isotope species differs from the recycling isotope species and the profile varies significantly depending on the ratio of the recycling isotope species, although the electron density profile shape is unchanged. The fast transition from nonmixing state to isotope-mixing state (nearly uniform profile of isotope ion density ratio) is observed associated with the change of electron density profile from peaked to hollow profile by the pellet injection near the plasma periphery. The transition from nonmixing to isotope-mixing state strongly correlates with the increase of turbulence measurements and the transition of turbulence state from TEM to ion temperature gradient is predicted by gyrokinetic simulation.

In the quiet regions on the solar surface, turbulent convective motions of granulation play an important role in creating small-scale magnetic structures, as well as in energy injection into the upper atmosphere. The turbulent nature of granulation can be studied using spectral line profiles, especially line broadening, which contains information on the flow field smaller than the spatial resolution of an instrument. Moreover, the Doppler velocity gradient along a line-of-sight (LOS) causes line broadening as well. However, the quantitative relationship between velocity gradient and line broadening has not been understood well. In this study, we perform bisector analyses using the spectral profiles obtained using the Spectro-Polarimeter of the Hinode/Solar Optical Telescope to investigate the relationship of line broadening and bisector velocities with the granulation flows. The results indicate that line broadening has a positive correlation with the Doppler velocity gradients along the LOS. We found excessive line broadening in fading granules, that cannot be explained only by the LOS velocity gradient, although the velocity gradient is enhanced in the process of fading. If this excessive line broadening is attributed to small-scale turbulent motions, the averaged turbulent velocity is obtained as 0.9 km/s., Comment: Accepted for publication in ApJ

Isotope effects of ECRH plasma in LHD were investigated in detail. A clear difference of transport and turbulence characteristics in H and D plasmas was found in the core region, with normalized radius ρ < 0.8 in high collisionality regime. On the other hand, differences of transport and turbulence were relatively small in low collisionality regime. Power balance analysis and neoclassical calculation showed a reduction of the anomalous contribution to electron and ion transport in D plasma compared with H plasma in the high collisionality regime. In core region, density modulation experiments also showed more reduced particle diffusion in D plasma than in H plasma, in the high collisionality regime. Ion scale turbulence was clearly reduced at ρ < 0.8 in high collisionality regime in D plasma compared with H plasma. The gyrokinetic linear analyses showed that the dominant instability ρ = 0.5 and 0.8 were ion temperature gradient mode (ITG). The linear growth rate of ITG was reduced in D plasma than in H plasma in high collisionality regime. This is due to the lower normalized ITG and density gradient. More hollowed density profile in D plasma is likely to be the key control parameter. Present analyses suggest that anomalous process play a role to make hollower density profiles in D plasma rather than neoclassical process. Electron scale turbulence were also investigated from the measurements and linear gyrokinetic simulations.

The isotope effect, which has been a long-standing mystery in the turbulent magnetically confined plasmas, is the phenomena that the plasma generated with heavier hydrogen isotope show a mitigated transport. This is on the contrary to what is predicted with the simple scaling theory, in which the heavier ions easily diffuse because of its larger gyro-radius. Thanks to the newly developed analysis method and a comprehensive parameter scan experiment in the steady-state plasmas in the Large Helical Device (LHD), the isotope effect was clearly observed in the self-organized internal transport barrier (ITB) structure for the first time. Comparing the ITB intensity in deuterium (D) and hydrogen (H) plasmas, two distinct hydrogen isotope effects are found: stronger ITB is formed in D plasmas and a significant edge confinement degradation accompanied by the ITB formation emerges in H plasmas. This observation sheds light on a new aspect of the turbulent plasmas regarding how the basic properties of the fluid material affect the turbulent structure formation in the open-system.

A quasi-axisymmetric stellarator, the CFQS, has been designed as a joint project of the National Institute for Fusion Science and Southwest Jiaotong University to prove intrinsic advantages of quasi-axisymmetry. Principal parameters of the CFQS are as follows: the major radius is 1 m, the magnetic field strength is 1 T, the aspect ratio is 4, and the toroidal periodic number is 2. The magnetic field configuration is designed based on that of the CHS-qa. Enhanced confinement properties within the context of neoclassical theory are achieved by its quasi-axisymmetric configuration. In the entire radial range, the magnetic well is retained to keep favourable stability features in the magnetohydrodynamic equilibrium. A magnetic field coil system was designed for the CFQS, which consists of 16 modular coils, 12 toroidal field coils, and 4 poloidal field coils. The supporting structure is designed to withstand strong electromagnetic force under 1 T operation, maintaining enough space for heating and diagnostic systems. The mock-up modular coil with the most complicated shape was constructed by Hefei Keye Electro Physical Equipment Manufacturing Co., Ltd. to check manufacturability and the achieved accuracy. A heat-run test was performed to check the temperature rise of conductors, and the capability of 1 T operation was confirmed. After various tests for the mock-up coil, construction of actual modular coils and the vacuum vessel has begun.

In this paper, the background physics of the isotope effects in the ion internal transport barrier (ITB) are discussed in detail. An heuristic criterion for the ITB strength is defined based on the nonlinear dependence of the ion thermal diffusivity on the local ion temperature in the L-mode phase. Comparing deuterium plasmas and hydrogen plasmas, two isotope effects on the ion ITB are clarified: stronger ITBs formed in the deuterium plasmas and an ITB concomitant edge confinement degradation in the hydrogen plasmas. Principal component analysis reveals that the ion ITB becomes strong when a high input power normalized by the line averaged electron density is applied and electron density profile is peaked. A gyrokinetic simulation suggests that the ITB profile is determined by the ion temperature gradient driven turbulence, while the way the profile saturates in L-mode plasmas is unknown. In the electron density turbulence behavior, a branch transition is observed, where the increasing trend in turbulence amplitude against the ITB strength is flipped to a decreasing trend across the ITB formation. The radial electric field structure is measured by the charge exchange recombination spectroscopy system. It is found that the radial electric field shear plays a minor role in determining the ITB strength.

A novel quasilinear turbulent transport model DeKANIS has been constructed founded on the gyrokinetic analysis of JT-60U plasmas. DeKANIS predicts particle and heat fluxes fast with a neural network (NN) based approach and distinguishes diffusive and non-diffusive transport processes. The original model only considered particle transport, but its capability has been extended to cover multi-channel turbulent transport. To solve a set of particle and heat transport equations stably in integrated codes with DeKANIS, the NN model embedded in DeKANIS has been modified. DeKANIS originally determined turbulent saturation levels semi-empirically based on JT-60U experimental data, but now it can also estimate them using a theory-based saturation rule. The new saturation model is still partly connected to experimental data, but it offers the potential for applying DeKANIS independently of the device.

A new numerical method for designing the external coils of a stellarator is presented. In this method, the shape of filamentary coils is expressed using fully three-dimensional B-spline curves that are not necessarily constrained on a winding surface. The control points of B-spline curves are optimized together with the coil position and current to minimize an objective function, which is defined using normal field components and engineering constraints. The genetic algorithm is employed to minimize the objective function for arbitrary combinations of modular, helical, and circular poloidal field coils without giving any specific initial guess of coil shapes. A new numerical code genetic optimizer using sequence of points for external coil is developed on the basis of this method, and successfully found optimized modular coils for the stellarators CFQS and Wendelstein 7-X. We also found a specific pattern of helical coil arrangement that can reproduce these optimized stellarators while creating divertor legs outside of the closed magnetic surfaces.

The isotope effect on impurities and bulk ion particle transport is investigated by using the deuterium, hydrogen, and isotope mixture plasma in the Large Helical Device (LHD). A clear isotope effect is observed in the impurity transport but not the bulk ion transport. The isotope effects on impurity transport and ion heat transport are observed as a primary and a secondary effect, respectively, in the plasma with an internal transport barrier (ITB). In the LHD, an ion ITB is always transient because the impurity hole triggered by the increase of ion temperature gradient causes the enhancement of ion heat transport and gradually terminates the ion ITB. The formation of an impurity hole becomes slower in the deuterium (D) plasma than the hydrogen (H) plasma. This primary isotope effect on impurity transport contributes the longer sustainment of the ion ITB state because the low ion thermal diffusivity can be sustained as long as the normalized carbon impurity gradient R/L n,c, where L c =-(∇n c/n c) -1 is above the critical value (∼-5). Therefore, the longer sustainment of the ITB state in the deuterium plasma is considered to be a secondary isotope effect due to the mitigation of the impurity hole. The radial profile of H and D ion density is measured using bulk charge exchange spectroscopy inside the isotope mixture plasma. The decay time of H ion density after the H-pellet injection and the decay time of D ion density after D-pellet injection are almost identical, which demonstrates that there is no significant isotope effect on ion particle transport.

Transport and confinement characteristics, and microinstabilities for high- and high- isotope plasmas in Large Helical Device are explored by using the gyrokinetic Vlasov simulation GKV with hydrogen isotope ions and real-mass kinetic electrons. The experimental data indicate that the thermal diffusivity is reduced in the deuterium-dominated plasmas, where the deviation from the gyro-Bohm scaling in the overall tendency and the strong anomaly of the electron heat transport are identified. Linear gyrokinetic analyses identify that the growth rates of the ion temperature gradient and trapped electron mode (TEM) instabilities in the deuterium plasmas are reduced due to the change in the profile gradients and/or the isotope ion mass, and the radial dependence of the mixing-length diffusivity is qualitatively consistent with the experimental tendency. Also, TEM-like turbulent fluctuations are examined by the using the phase contrast imaging measurement and the linear gyrokinetic calculation for the high- deuterium plasma.

The effect of magnetic shear on plasma transport for an electron to ion temperature ratio (T e/T i) near unity has been explored in DIII-D utilizing electron cyclotron heating (ECH). Previous reports showed that significant confinement degradation occurred at T e/T i ∼ 1 in positive shear (PS) plasmas in DIII-D, whereas reduced confinement degradation was observed in negative central shear (NCS) plasmas. In this study, plasma transport in weak magnetic shear (WS) plasmas with ECH is investigated and compared with that in NCS and PS plasmas. Here the magnetic shears ( s ˆ ) are s ˆ > 0.5, ∼0 and ρ∼ 0.3–0.4) of PS, WS and NCS plasmas, respectively, and flat or negative inside ρ∼ 0.4 in the WS and NCS plasmas. Weak magnetic shear is found to be effective in minimizing degradation of ion thermal confinement as T e/T i increases through ECH application, and an improved confinement factor of H 98y2 ∼ 1.2 is maintained, similar to NCS plasmas. At T e/T i ∼ 1, the ion thermal diffusivity around an internal transport barrier decreases when changing the magnetic shear from positive to weak or negative shear. Also, reduced local particle and momentum transport was indicated by steeper density and toroidal rotation profiles in the weak and negative shear regimes. Linear gyrokinetic simulations predict little change in growth rates of low-k turbulence with ECH application in the WS and NCS plasmas, which is consistent with the transport and profile analyses.

Characteristics of plasma parameters and turbulence in the isotope-mixing and the non-mixing states in hydrogen-deuterium mixture plasmas in the large helical device are discussed. The isotope mixing state is characterized by the uniform isotope ratio profile regardless of the location of the particle source of each species in the isotope mixture plasma. The isotope non-mixing state is identified by the non-uniform isotope ratio profile measured with bulk charge exchange spectroscopy when the beam fueling isotope species differs from the recycling isotope species. The effect of collisionality, T e / T i ratio, sign of density gradient on transition between isotope mixing and non-mixing is discussed. The plasma parameters preferable for the non-mixing state are found to be lower collisionality, higher T e / T i , and negative or zero density gradient (peaked or flat density profile). The time scale of transition from non-mixing to mixing is evaluated by the hydrogen and deuterium pellet injection near the plasma edge and is found to be less than 5 ms, which is much shorter than the particle confinement time. The strong correlation between isotope mixing and turbulence characteristics is observed. This strong correlation suggests the change in turbulence is a strong candidate for the mechanism causing the transition between uniform and non-uniform isotope density ratio profiles.

A linearized collision operator, which preserves the conservation properties of particles, momentum, and energy, and the self-adjointness relation (H-theorem) for arbitrary particle species, is applied to Eulerian kinetic simulations of multi-species ions and electrons. Velocity-space grid number scans clarify that numerical errors in like-particle and unlike-ion collisions are sufficiently small under turbulence-simulation relevant resolutions. For electron–ion/ion–electron collisions, it is identified that highly steep and localized nature in the velocity-space leads to relatively larger conservation errors in the standard implementation without error corrections. In order to resolve such numerical difficulties, a modified field-particle operator based on the original one is newly constructed, so that the conservation properties are improved to achieve the round-off error levels. It is confirmed that the modified collision operator successfully reproduces the collisional relaxation of multi-species ions and electrons towards their equilibrium distributions satisfying the H-theorem.

The turbulent transport of magnetic confinement plasmas including multi-ion-particle-species in helical systems such as the Large Helical Device (LHD) [Takeiri et al., Nucl. Fusion 57, 102023 (2017)] and their plasma profile sensitivities are investigated by local flux-tube gyrokinetic simulations. In the multi-ion-species plasmas, while the heat transport of each particle species has slightly different sensitivity towards the plasma temperature gradients and the density gradients, there exist quite different dependencies in the particle transport on the radial gradient profiles of the plasma temperatures and densities between each particle species. Furthermore, in the LHD plasma with the carbon impurity hole structure [Ida et al., Plasma Phys. 16, 056111 (2009)], the turbulent particle transport flux of the impurity carbon ion remains radially inward-directed robustly within the wide ranges of radial gradient profiles of the plasma temperatures and densities.

Positive isotope effects have been found in electron cyclotron resonant heating plasma of the Large Helical Device (LHD). The global energy confinement time (τE) in deuterium (D) plasma is 16% better than in hydrogen (H) plasma for the same line-averaged density and absorption power. The power balance analyses showed a clear reduction in ion energy transport, while electron energy transport does not change dramatically. The global particle confinement time (τp) is degraded in D plasma; τp in D plasma is 20% worse than in H plasma for the same line-averaged density and absorption power. The difference in the density profile was not due to the neutral or impurity sources, but rather was due to the difference in the transport. Ion scale turbulence levels show isotope effects. The core turbulence (ρ = 0.5–0.8) level is higher in D plasma than in H plasma in the low collisionality regime and is lower in D plasma than in H plasma. The density gradient and collisionality play a role in the core turbulence level.

The deuterium (D) operation was initiated in the LHD in 2017. In the first campaign of the D experiments, we successfully extended the high temperature regime in the LHD. The new record of the ion temperature (Ti) of 10 keV associated with the ion internal transport barrier (ITB) was achieved due to several operational optimization. The thermal confinement characteristics of ITB plasmas were compared between hydrogen and D discharges. The effective ion thermal diffusivity of the ion-ITB plasmas was found to be smaller in the D discharges than that in the H discharges. The profiles of the Ti, the electron density, and the impurity of the high Ti plasmas strongly depended on the magnetic configuration and these profiles tended to peaked in the inward-shifted configuration. It was also found that the electron thermal confinement of the electron-ITB plasmas was clearly improved in the deuterium case. The GKV simulation showed the linear growth rate of TEM/ITG reduced in the plasmas with D both for the ion ITB and the electron ITB plasmas and qualitatively agreed with the tendency of the change in the thermal diffusivity obtained from the power balance analysis.

Impacts of isotope ion mass on trapped-electron-mode (TEM)-driven turbulence and zonal flows in magnetically confined fusion plasmas are investigated. Gyrokinetic simulations of TEM-driven turbulence in three-dimensional magnetic configuration of helical plasmas with hydrogen isotope ions and real-mass kinetic electrons are realized for the first time, and the linear and the nonlinear nature of the isotope and collisional effects on the turbulent transport and zonal-flow generation are clarified. It is newly found that combined effects of the collisional TEM stabilization by the isotope ions and the associated increase in the impacts of the steady zonal flows at the near-marginal linear stability lead to the significant transport reduction with the opposite ion mass dependence in comparison to the conventional gyro-Bohm scaling. The universal nature of the isotope effects on the TEM-driven turbulence and zonal flows is verified for a wide variety of toroidal plasmas, e.g., axisymmetric tokamak and non-axisymmetric helical or stellarator systems.

Transport studies of pellet fuelling experiments on LHD are reported. Spatio-temporal evolutions after pellet injection into LHD discharges show cases where central density increases on the time scale of particle transport processes. Both the temperature gradient and the density gradient change during the density relaxation, the latter even in sign. The resulting thermodynamic forces influence radial electric fields - both as a driving term but also by, e.g. affecting the E r dependence of ion transport. Magnetic fluctuations have been found to be induced by pellet injection but die out with the relaxation of the pressure profile.

The effects of misalignment of modular coils on various physical properties in the Chinese first quasi-axisymmetric Stellarator (CFQS) are discussed in this study. To estimate the effects quantitatively, simple assumptions are made regarding the structure of coil displacement. We consider the following three cases: displacement in radial direction (Case A), displacement in the vertical direction (Case B), and displacement by tilting (Case C). In all cases, we assume that the displacement structure has a stellarator symmetry. These assumptions are employed to calculate the change in the magnetic surfaces, rotational transform profile, magnetic well depth profile, and the effective helical ripple. Calculation results show that if the magnitude of displacement is less than 10 mm, the effects on these physical properties are small, and the good neoclassical transport property is retained.

The transfer rate of the entropy variable in the wavenumber space perpendicular to the equilibrium magnetic field is evaluated by means of the gyrokinetic simulations of the toroidal ion temperature gradient turbulence. Fluctuations of the perturbed gyrocenter distribution function of the linearly unstable mode are transferred to those with higher radial wavenumbers through interactions with zonal flows driven by turbulence. The entropy transfer rate coincides with the zonal flow shearing rate in cases with weak ion temperature gradient where the zonal flows effectively regulate the turbulent transport. The obtained result verifies a correlation between the entropy transfer and the zonal flow shearing processes.

Since the observation of impurity hole in LHD, which contradicts the prediction of the conventional neoclassical transport theory, several attempts have been made to explain the mechanism behind the phenomenon. Consideration of the impact of electrostatic potential variation within the flux surface, Φ1, is one of those attempts. However, all of the numerical studies that have investigated the effect of Φ1 to date have been conducted with local simulation codes, and no global calculation has been performed yet. Here, a global neoclassical simulation code FORTEC-3D is applied to evaluate Φ1, including the global effects, for the first time. The global simulation result for a high-temperature low-density plasma, which corresponds to an impurity hole plasma, shows significant difference from the local simulation results in the Φ1 profile. This indicates that consideration of the global effects is essential for quantitative evaluation of impurity neoclassical transport in an impurity hole plasma.

The world's newest quasi-axisymmetric stellarator CFQS is constructed as a joint project of the National Institute for Fusion Science, Japan and Southwest Jiaotong University, the People's Republic of China. The project is named “NSJP for CFQS”. The CFQS has a major radius of 1 m, toroidal periods of 2, and aspect ratio of 4. The toroidal magnetic field strength will be increased up to 1 T. The CFQS equilibrium is characterized by low-aspect ratio and quasi-axisymmetry, having both natures of two-dimensional tokamak and three-dimensional stellarator. The CFQS offers new opportunities and fields to increase understanding of toroidal fusion plasmas.

Transport simulation for the electron and ion temperature profiles is performed in helical plasmas by using the heat diffusivity models and the quasilinear flux models [S. Toda et al., Phys. Plasmas 26, 012510 (2019)] for the electron and ion heat turbulent transport. The turbulent transport for the nonlinear simulation results can be evaluated by these models. The high-Ti and low-Ti plasmas for the discharge in the Large Helical Device (LHD) are studied, where the ion temperature gradient mode is unstable. The electron and the ion temperature profiles of the dynamical simulation results do not contradict with those of the experimental results in the LHD. For the plasmas of the LHD in this study, the transport simulation results by the diffusivity models and the quasilinear flux models for the heat transport to reproduce the nonlinear simulation results in the allowable errors are found to explain the experimental results for the temperature profiles.

The particle and heat transport driven by the ion temperature gradient instability in helical plasmas is investigated by the gyrokinetic analysis taking into account the kinetic electron response. High and low ion temperature plasma cases for the discharge in the Large Helical Device (LHD) are studied. Two types of transport models with a lower computational cost to reproduce the nonlinear gyrokinetic simulation results within allowable errors are presented for application in quick transport analyses. The turbulent electron and ion heat diffusivity models are given in terms of the linear growth rate and the characteristic quantity for the linear response of zonal flows, while the model of the effective particle diffusivity is not obtained for the flattened density profile observed in the LHD. The quasilinear flux model is also shown for the heat transport. The quasilinear flux models for the energy fluxes are found to reproduce the nonlinear simulation results at the accuracy similar to that of the heat diffusivity models. In addition, the quasilinear particle flux model, which is applicable to the transport analysis for LHD plasmas, is constructed. These turbulent reduced models enable coupling to the other simulation in the integrated codes for the LHD.

Neutral endopeptidase (NEP) is present on various epithelial cells and inactivates numerous physiologically active peptides. Neutral endopeptidase may regulate proinflammatory signals in oral mucosal epithelium. However, the function of NEP in oral mucosal epithelium is unknown. The present study investigated the action of NEP upon proinflammatory signals on human oral keratinocytes and the influence of endothelin-converting enzyme (ECE)-1, an enzyme similar to NEP, on the functions of NEP. Oral keratinocytes were cultured in medium containing inflammatory inducers [lipopolysaccharide (LPS) and nicotine], NEP inhibitors, and ECE-1/NEP inhibitors, either alone or in combination. The concentrations of substance P (SP) and interleukin-1β (IL-1β) were measured in the supernatant. Additionally, the concentrations of SP and IL-1β were measured in the supernatant of cells incubated with LPS or nicotine after transfection with NEP small interfering RNA (siRNA). The concentrations of SP and IL-1β were significantly increased in cells incubated with NEP inhibitors and, to a lesser extent, in cells incubated with ECE-1/NEP inhibitors, compared with controls (cells incubated with LPS or nicotine alone). The concentrations of SP and IL-1β in cells transfected with NEP siRNA were significantly augmented compared with controls. In conclusion, the present study demonstrated that NEP down-regulated the levels of SP and IL-1β produced from human oral keratinocytes, although ECE-1 may be partly related to the down-regulation.

Plasma turbulence research based on five-dimensional (5D) gyrokinetic simulations is one of the most critical and demanding issues in fusion science. To pioneer new physics regimes both in problem sizes and in timescales, an improvement of strong scaling is essential. Overlap of computations and communications using non-blocking MPI communication schemes is a promising approach to improving strong scaling, but it often fails on practical applications with conventional MPI libraries. In this work, this classical issue is resolved by developing communication-overlap techniques with additional MPI support for non-blocking communication routines and with heterogeneous OpenMP threads, which work even on conventional MPI libraries and network hardware. These techniques dramatically improved the parallel efficiency of a gyrokinetic toroidal 5D Eulerian code GT5D on the K-computer, which has a dedicated network, and on the Helios system which has a commodity network. On the K-computer, excellent strong scaling was achieved beyond 100k cores whilst keeping a sustained performance of [Formula: see text]10% ([Formula: see text]307 TFlops using 196,608 cores), and simulations for next-generation large-scale fusion experiments are significantly accelerated. This performance is 16[Formula: see text] sped up compared with the maximum performance reported at the 2011 International Conference for High Performance Computing, Networking, Storage and Analysis ([Formula: see text]19 TFlops using 16,384 cores of the BX900 cluster) (Idomura, 2011).

Benchmark between electromagnetic gyrokinetic codes GKV and GENE based on the flux tube model has been carried out by employing the high performance tokamak experiment data. The constructed flux coordinates, linear dispersion relation, and nonlinear turbulent transport show good agreements. Utilizing these codes, linear mode structures of micro-tearing modes have been examined. It is found that the current density is highly localized in the radial direction and peaks on the inner board side of the torus, while the broaden O-shape structure is observed on the torus outer board side. This broadening originates from the magnetic drift, that is, the finite orbit width of passing particles.

A neutron emission rate analysis code called FBURN, based on the classical energetic ion confinement assumption with radial diffusion, is developed for the time-dependent analysis of the total neutron emission rate (Sn) in neutral beam (NB) heated deuterium plasmas. The time trend of Sn evaluated by FBURN shows good agreement with the Sn measured by the neutron flux monitor on the deuterium operation of the Large Helical Device. The dependence of Sn on line-averaged electron density (ne_avg) has a peak at ne_avg of around 2.5 × 1019 m−3 in both experiment and calculation. Here, the absolute value of Sn evaluated by calculation agrees with that obtained in experiments within a factor of two. A time trend analysis of Sn in an electron cyclotron heated plasma with a short pulse NB injection is performed. The analysis shows that the diffusion coefficient of co-going transit beam ions is 0.2 to 0.3 m2 s−1. In addition, the diffusion coefficient of helically trapped beam ions decreases from 5 to 3 m2 s−1 with the inward shift of the magnetic axis position. Time-resolved analysis of the triton burnup experiment shows that the diffusion coefficient of tritons is around 0.15 m2 s−1. It is found that the diffusion coefficients of the beam and tritons are of a similar value as obtained in JT-60U. The trend of the triton burnup ratio on the ne_avg calculated by the FBURN agrees with the experiments. The results suggest that the decrease of the triton burnup ratio with the increase of ne_avg is due to the shorter slowing down time of tritons by the decrease of the electron temperature, and the increase of the triton burnup ratio with the increase of ne_avg is due to the diffusion of tritons. Time trend analysis of Sn in the Korea Superconducting Tokamak Advanced Research and the Experimental Advanced Superconducting Tokamak plasmas with a short pulse NB injection is performed. The time trend of Sn is successfully reproduced by FBURN.

In the framework of the flux-matching method, which is a useful way for the validation of the gyrokinetic turbulence simulations, it is strongly demanded to evaluate the plasma profile sensitivity of the transport coefficients obtained in the employed simulation model within the profile gradient ranges estimated from the experimental observations. The sensitivity causes the plasma profile stiffness for wide ranges of the transport fluxes. In the nonlinear gyrokinetic simulations for the ion temperature gradient (ITG) turbulence in the Large Helical Device (LHD) [Takeiri et al., Nucl. Fusion 57, 102023 (2017)], it is found that the temperature gradients around the experimental nominal observations are slightly larger than the threshold of the instability, and the ion heat diffusivities are quite sensitive to the temperature gradient. The growth rates of the instability, the generations of the zonal flows, and the sensitivities of the transport coefficients to the temperature profiles depend on the radial locations, the employed simulation models, and the field configurations. Specifically, in the optimized LHD field configuration, the sensitivities are relaxed in the outer radial region due to the enhancement of the zonal flows and the reduction of the ITG instability. In order to estimate the range of the temperature gradients possible given the experimentally obtained data of the temperature with errorbars, the statistical technique, Akaike's Information Criterion [H. Akaike, in Proceedings of the 2nd International Symposium on Information Theory, edited by B. N. Petrov and F. Caski (Akadimiai Kiado, Budapest, 1973), pp. 267–281] is applied. Against the range of the temperature gradients, the flux-matching method to predict the temperature gradient in helical plasmas is demonstrated.In the framework of the flux-matching method, which is a useful way for the validation of the gyrokinetic turbulence simulations, it is strongly demanded to evaluate the plasma profile sensitivity of the transport coefficients obtained in the employed simulation model within the profile gradient ranges estimated from the experimental observations. The sensitivity causes the plasma profile stiffness for wide ranges of the transport fluxes. In the nonlinear gyrokinetic simulations for the ion temperature gradient (ITG) turbulence in the Large Helical Device (LHD) [Takeiri et al., Nucl. Fusion 57, 102023 (2017)], it is found that the temperature gradients around the experimental nominal observations are slightly larger than the threshold of the instability, and the ion heat diffusivities are quite sensitive to the temperature gradient. The growth rates of the instability, the generations of the zonal flows, and the sensitivities of the transport coefficients to the temperature profiles depend on the radial l...

Time-resolved measurement of triton burnup is performed with a scintillating fiber detector system in the deuterium operation of the large helical device. The scintillating fiber detector system is composed of the detector head consisting of 109 scintillating fibers having a diameter of 1 mm and a length of 100 mm embedded in the aluminum substrate, the magnetic registrant photomultiplier tube, and the data acquisition system equipped with 1 GHz sampling rate analogies to digital converter and the field programmable gate array. The discrimination level of 150 mV was set to extract the pulse signal induced by 14 MeV neutrons according to the pulse height spectra obtained in the experiment. The decay time of 14 MeV neutron emission rate after neutral beam is turned off measured by the scintillating fiber detector. The decay time is consistent with the decay time of total neutron emission rate corresponding to the 14 MeV neutrons measured by the neutron flux monitor as expected. Evaluation of the diffusion coefficient is conducted using a simple classical slowing-down model FBURN code. It is found that the diffusion coefficient of triton is evaluated to be less than 0.2 m2 s−1.