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The horse (Equus caballus) varieties from Skyros and Rhodes islands (Greece) in the Aegean archipelago are extremely small, reaching shoulder heights of only about 1 m. Furthermore, the Japanese archipelago is home to eight small, native horse breeds. We investigated the evolutionary morphology and provided a review of historical documentations of these horses of cultural interest in Greece and Japan, thus providing a comparison of the independent evolution of small size in islands. We integrate cranial data from historical literature with data from newly gathered and curated skulls and analyse a measurement dataset featuring various domestic and mainland horse breeds and varieties. We use non-invasive imaging to study and measure 3D models of the bony labyrinth, housing the inner ear, and the braincase endocast. When considering the effects of allometry by regressing each PC1 scores (for each set of measurements) with the cranial geometric mean from linear measurements as a body size proxy, we show that size explains a large amount of the shape variation in horse crania, the bony labyrinths and brain endocasts. We found high intrabreed variation in all the analysed datasets. Globally, there are at least 30 distinct horse populations on islands, offering the chance to further study processes of convergence in morphological divergence and evaluate the effect of drift and the environment.

Proton-boron (p11B) fusion is an attractive potential energy source but technically challenging to implement. Developing techniques to realize its potential requires first developing the experimental capability to produce p11B fusion in the magnetically-confined, thermonuclear plasma environment. Here we report clear experimental measurements supported by simulation of p11B fusion with high-energy neutral beams and boron powder injection in a high-temperature fusion plasma (the Large Helical Device) that have resulted in diagnostically significant levels of alpha particle emission. The injection of boron powder into the plasma edge results in boron accumulation in the core. Three 2 MW, 160 kV hydrogen neutral beam injectors create a large population of well-confined, high -energy protons to react with the boron plasma. The fusion products, MeV alpha particles, are measured with a custom designed particle detector which gives a fusion rate in very good relative agreement with calculations of the global rate. This is the first such realization of p11B fusion in a magnetically confined plasma., source:Magee, R.M., Ogawa, K., Tajima, T. et al. First measurements of p11B fusion in a magnetically confined plasma. Nat Commun 14, 955 (2023). https://doi.org/10.1038/s41467-023-36655-1, source:https://doi.org/10.1038/s41467-023-36655-1, identifier:0000-0001-6697-7891

source:47th EPS Conference on Plasma Physics O2.103, source:https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwik5L6aibX9AhVVBN4KHWeHDQAQFnoECAwQAQ&url=http%3A%2F%2Focs.ciemat.es%2FEPS2021PAP%2Fpdf%2FO2.103.pdf&usg=AOvVaw0rcW0sXbthmLb0nMM-tppr

Effects of low-n magnetohydrodynamic instabilities on plasma performance have been assessed in the regime where an achieved beta value is limited by instabilities. The unstable regime of an ideal interchange mode is characterized by enhanced magnetic hill and reduced magnetic shear. Experiments have clarified that (i) low-n modes are significantly destabilized in the ideal-unstable configurations and lead to degradation of central beta by at most 60%, and (ii) the degree of their damages strongly depends on the mode rotation velocity. The occurrence of the minor collapse is independent of an existence of an error field., source:S. Sakakibara et al 2015 Nucl. Fusion 55 083020, source:https://doi.org/10.1088/0029-5515/55/8/083020, identifier:0000-0002-3306-0531

The internal mode structure of a precursor with the tearing-parity structure of the locked-mode-like instability is investigated. For the first time, the Thomson scattering system with high temporal and spatial resolution enables us to find the non-rotating temperature flattening region in the torus outboard side in addition to the rotating island during the slowing-down phase. Additionally, the width of the flattening region is 10% normalized by the plasma minor radius. Furthermore, the radial profiles of the pressure degradation during the slowing-down phase are evaluated. At the beginning of the slowing-down phase, the pressure degradation area is located slightly inside the resonant surface. After that, the peak location moves to the core region. Finally, the degradation area peaks at the plasma center., source:https://doi.org/10.1585/pfr.16.1402091, identifier:0000-0003-3754-897X

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., source:https://doi.org/10.1088/1741-4326/ac3cda, identifier:0000-0001-5220-947X

A 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., source:To cite this article: K. Ogawa, M. Isobe, H. Nuga, R. Seki, S. Ohdachi & M. Osakabe (2022) Evaluation of Alpha Particle Emission Rate Due to the p-11B Fusion Reaction in the Large Helical Device, Fusion Science and Technology, 78:3, 175-185, DOI: 10.1080/15361055.2021.1973294, source:https://doi.org/10.1080/15361055.2021.1973294, identifier:0000-0003-4555-1837

Imaging diagnostics offers magnetic free information for the plasma emissions and able to define plasma shape and position, impurity distribution, and magnetohydrodynamics (MHD) instabilities. The tomographic reconstruction is one of the powerful tools to analyze imaging diagnostic data. Tomography is employed for a wide range of plasma studies prominently for the soft X-ray (SX). SX tomography allows access to spatiotemporal transient phenomena resulting from the magnetohydrodynamics (MHD) activities, which are important for plasma confinement. Heliotron J (H-J) is an L/M = 1/4 helical axis Heliotron with a low magnetic shear configuration and with a bumpy poloidal plasma shape. An attempt for qualitative evaluation of the tomographic reconstruction capabilities for the Heliotron-J device was made. The tomographic reconstructions were made via Phillips - Tikhonov regularizations from the experimental data set at different locations in the time-space. The results suggests that the diagnostic needs to be improved for a high quality of image reconstruction and possible realization of magnetic axis shift, Shafranov Shift., source:https://doi.org/10.1585/pfr.14.3402056, identifier:0000-0002-1959-0333

In recent years, fusion research has become exceedingly popular in the Asian region. Many toroidal devices are currently operated for fusion research in universities and institutes. The long pulse operation of a high-performance plasma is also possible in four superconducting devices, which are EAST (Institute of Plasma Physics Chinese Academy of Sciences (ASIPP), China), KSTAR (National Fusion Research Institute (NFRI), Korea), LHD (National Institute for Fusion Science (NIFS), Japan) and SST-1 (Institute for Plasma Research (IPR), India). The world's largest superconducting tokamak, JT-60SA (National Institutes for Quantum and Radiological Science and Technology (QST), Japan), and middle-size tokamak, HL-2M (Southwestern Institute of Physics (SWIP), China), have now been constructed for the upcoming operation. Based on the progressive development of fusion research in Asian region an international collaboration on critical physics for the steady state operation of high-performance plasmas has been carried out among China, Japan and Korea during past five years through the A3 foresight program. Recent fusion research activities in the Asian region and the results of the collaboration are briefly reported with future prospects for international collaboration., source:https://doi.org/10.1585/pfr.13.3502046, identifier:0000-0003-4139-7721

Tomographic reconstruction of the emission profile is a typical ill-posed inversion problem. It becomes troublesome in fusion plasma diagnostics because the possible location/direction of the observation is quite limited. In order to overcome the difficulty, many techniques have been developed. Among them, series expansion methods are based on decomposing the emission profile with orthogonal or nearly orthogonal basis patterns. Since it is possible to ignore the surplus components with higher spatial frequency, this type of method is robust against noise issues. Two topics are discussed in this article. The first issue is the comparison of the basis systems themselves. Conventional one of Fourier-Bessel and a new one of the so-called Laplacian eigen function are compared from the viewpoint of the capability of expressing the patterns that appear in the fusion plasma experiment. The second issue is the application to the tangential viewing imaging system. It is shown that, even from the limited information, tomographic reconstruction can be adequately performed with appropriate use of the regularization, especially with the use of the L1 regularization., source:https://doi.org/10.1585/pfr.14.3402087 Details, identifier:0000-0001-6286-8874

Effects of poloidal shear flow on the stability of interchange modes in a Large Helical Device (LHD) configuration are numerically studied. Three-dimensional (3D) numerical codes are utilized for the equilibrium and stability calculations. A static equilibrium is employed and a model poloidal flow as a flux function is incorporated in the initial perturbation. The results show that the initially applied flow can suppress the growth of the interchange mode if the flow is sufficiently large., source:https://doi.org/10.1585/pfr.11.2403035, identifier:0000-0002-7698-0223

In order to clarify the mechanism responsible for slowing down the precursor of an instability in Large Helical Device (LHD), whose behavior is similar to the locked mode instability in tokamaks, the spatial structure of the precursor of the locked-mode-like instability, and the relationship between the rotation of the precursor and the E × B rotation were experimentally investigated. The precursor rotates together with the E × B rotation at the resonant surface, and the precursor rotation slows down because of a decrease of the E × B rotation. The multi-channel fluctuation measurement of the precursor suggests that the precursor has a magnetic island, which may be related to the decrease of the E × B rotation. In addition, the reason for the appearance of the precursor with a magnetic island is discussed. The precursor appears when a magnetic island grows initially without rotation but then shrinks and begins to rotate., source:https://doi.org/10.1585/pfr.12.1402028, identifier:0000-0003-3754-897X

Edge MHD instabilities with pressure collapse are found in relatively high beta and low magnetic Reynolds number regions with a magnetic axis torus outward-shifted configuration of the large helical device (LHD), and characteristics and onset conditions of the instability are investigated. The instability has a radial structure with an odd parity around the resonant surface, which is different from that of the interchange instability typically observed in the LHD. The onset condition dependence on the magnetic axis location shows that the onset beta increases as the magnetic axis location moves more torus inwardly, and the instability appears only in limited configurations where the magnetic axis is located between 3.65 and 3.775 m. In such configurations, the resonant surface location is close to an index of the plasma boundary. This fact suggests that the distance between the resonant surface location and the plasma boundary plays an important role in the onset, and a possibility that the instability is driven by an external mode., source:https://doi.org/10.1063/5.0111360, identifier:0000-0003-3754-897X

The rotation of resistive interchange instabilities excited in the periphery of plasmas compared to plasma flows under various plasma conditions in the Large Helical Device. The observed magnetohydrodynamic modes exhibit nominal rotation in the electron diamagnetic direction in the laboratory frame. We assumed that the ion (electron) flows consist of the E × B and ion (electron) diamagnetic drift flows. These drift flows were individually evaluated and geometrically compensated using a finite beta equilibrium. Experiments with different neutral beam injection conditions and different electron densities show that the frequencies of the observed modes were quantitatively consistent with those of the electron flow., source:https://doi.org/10.1585/pfr.8.1402123, identifier:0000-0003-3754-897X

The magnetic island in the large helical device (LHD) shows the dynamic behaviour of the healing/growth transition withthe hysteretic behaviour. The thresholds of plasma beta and poloidal flow for island healing are larger than that for growth.The threshold of resonant magnetic perturbation (RMP) for healing is smaller than that for growth. Furthermore, thresholds of the amplitude of RMP depend on the magnetic axis position Rax in the LHD. The RMP threshold increases as the magnetic axis position Rax increases. The poloidal viscosity may be considered as a candidate to explain the experimental observation from the viewpoint of the relationship between the electromagnetic torque and the viscous torque., source:https://iopscience.iop.org/article/10.1088/0029-5515/55/7/073004

The mechanism of the partial collapse observed in the experiment with the background magnetic field changing in the Large Helical Device (LHD) is numerically investigated with a nonlinear magnetohydrodynamics (MHD) simulation. Since the different timescales of the perturbations and the background field changing have to be treated simultaneously for the analysisof this plasma, a multi-scale simulation scheme is developed. The effect of the perturbation dynamics on the equilibrium pressure and rotational transform is taken into account in this scheme. The result indicates that the collapse is caused by the destabilization of an infernal-like mode due to the magnetic hill enhanced by the change of the background field. The mechanismof the reduction of the central beta observed after the partial collapse in the experiment is also analysed in relation to the effect of the background field changing., source:Ishiguchi K, Sakakibara S, Ohdachi S and Carreras B.A. 2015 Multi-scale MHD analysis of LHD plasma with background field changing Nuclear Fusion 55 043019., source:https://doi.org/10.1088/0029-5515/55/4/043019, identifier:0000-0002-7698-0223

This paper provides a software application of the sampling scope concept for fusion research. The time evolution of Thomson scattering data is reconstructed with a high temporal resolution during a modulated electron cyclotron resonance heating (MECH) phase. The amplitude profile and the delay time profile of the heat pulse propagation are obtained from the reconstructed signal for discharges having on-axis and off-axis MECH depositions. The results are found to be consistent with the MECH deposition., source:Review of Scientific Instruments 87, 043505 (2016); https://doi.org/10.1063/1.4945258, source:https://doi.org/10.1063/1.4945258, identifier:0000-0001-5669-1937

A remarkable extension of the high-ion-temperature (high-Ti) regime was obtained in deuterium plasma experiments in the Large Helical Device. In order to clarify transport characteristics in the ion internal transport barrier (ITB) formation with an isotope effect, a dataset of pure deuterium (nD/ne > 0.8) and pure hydrogen (nH/ne > 0.8) plasmas in the high-Ti regime were analyzed, and two mechanisms of transport improvement were characterized. A significant reduction of ion heat transport in the core of both deuterium and hydrogen plasmas was observed, indicating ion ITB formation. The dependence of the ion heat diffusivity on temperature ratio (Te/Ti) and normalized Ti-gradient (R/LTi = −(R/Ti)(dTi/dr)) was investigated in the core region, in which gyrokinetic simulations with the GKV code predict the destabilization of ion temperature gradient (ITG) modes. The Te/Ti dependence shows ITG-like property, while a significant deviation from the ITG-like property is found in the R/ dependence, indicating suppression of the ITG mode in the large R/ regime and resultant ion ITB formation. In the comparison between deuterium plasma and hydrogen plasma, the lower transport in the deuterium plasma is observed in both ion and electron heat diffusivities, indicating a significant isotope effect. It was found with the nonlinear turbulent transport simulation with GKV that the zonal flow enhancement contributes to the ITG suppression in the deuterium plasma., source:K. Nagaoka et al 2019 Nucl. Fusion 59 106002, source:https://doi.org/10.1088/1741-4326/ab2d02, identifier:0000-0002-5892-6047

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., source:H. Takahashi et al 2018 Nucl. Fusion 58 106028, source:https://doi.org/10.1088/1741-4326/aad87e

A new type of wavelet-based analysis for the magnetic fluctuations by which toroidal mode number can be resolved is proposed. By using a wavelet, having a different phase toroidally, a spectrogram with a specific toroidal mode number can be obtained. When this analysis is applied to the measurement of the fluctuations observed in the large helical device, MHD activities having similar frequency in the laboratory frame can be separated from the difference of the toroidal mode number. It is useful for the non-stationary MHD activity. This method is usable when the toroidal magnetic probes are not symmetrically distributed., source:Review of Scientific Instruments 87, 11D411 (2016); https://doi.org/10.1063/1.4959943, source:https://doi.org/10.1063/1.4959943

The aim of this study is to perform a theoretical analysis of the magnetohydrodynamic (MHD) stability and energetic particle effects on a LHD equilibria, calculated during a discharge where energetic-ion-driven resistive interchange mode (EIC) events were triggered. We use the reduced MHD equations to describe the linear evolution of the poloidal flux and the toroidal component of the vorticity in a full 3D system, coupled with equations of density and parallel velocity moments for the energetic particles species, including the effect of the acoustic modes, multiple energetic particles (EP) species, helical couplings and helically trapped EP. We add the Landau damping and resonant destabilization effects using a closure relation. The simulations suggest that the helically trapped EP driven by the perpendicular neutral beam injector (NBI) further destabilizes the 1/1 MHD-like mode located at the plasma periphery (r/a = 0.88). If the of the EP driven by the perpendicular NBI is larger than 0.0025 a 1/1 EIC with a frequency around 3 kHz is destabilized. If the effect of the passing EP driven by the tangential NBI is included on the model, any enhancement of the injection intensity of the tangential NBI below leads to a decrease of the instability growth rate. The simulations indicate that the perpendicular NBI EP is the main driver of the EIC events, as it was observed in the experiment. If the effect of the helical couplings are added in the model, an 11/13 EIC is destabilized with a frequency around 9 kHz, inward shifted (r/a = 0.81) compared to the 1/1 EIC. Thus, one possible explanation for the EIC frequency chirping down from 9 to 3 kHz is a transition between the 11/13 to the 1/1 EIC due to a weakening of the destabilizing effect of the high n modes, caused by a decrease of the EP drive due to a loss of helically trapped EP or a change in the EP distribution function after the EIC burst. The experimental data during the EIC bursting phase shows a complex mode, source:J. Varela et al 2019 Nucl. Fusion 59 046008, source:https://doi.org/10.1088/1741-4326/aaff80, identifier:0000-0002-6114-0539

The mode slowing down mechanism of the locked-mode-like instability without a large magnetic island is investigated, based on the LHD experimental analysis. The mode frequency coincides with E × B rotation frequency at the resonant surface and the slowing down is caused by two processes. One is the resonant surface moving to the small E × B rotation frequency region and the other is the slowing down of the E × B rotation frequency near the resonant surface. Both processes are almost the same as those of the locked-mode-like instability with a large magnetic island. The results suggest that the slowing down occurs even though the precursor does not have a large magnetic island. However, when the external RMP is imposed, the mode frequency in the slowing down phase sometimes does not coincide with the E × B rotation frequency. Moreover, the mode amplitude during the slowing down phase increases with the decrease of the mode frequency both with and without the imposed external RMP, which suggests that the instability growth in the slowing down phase is more strongly related to the mode frequency than the E × B rotation frequency because the mode sometimes does not rotate with the E × B rotation., source:Y. Takemura et al 2019 Nucl. Fusion 59 066036, source:https://doi.org/10.1088/1741-4326/ab169f, identifier:0000-0003-3754-897X

The slowing-down mechanism of the locked-mode-like instabilities with and without an island structure is investigated through the effects of an external RMP (resonant magnetic perturbation) on the instabilities. For both instabilities, the slowing-down duration decreases with the increase in the external RMP, and the RMP dependence is consistent with the braking model of the j × B force due to the interaction between the instabilities and the external RMP. Moreover, the relationship between the amplitude and the frequency of both locked-mode-like instabilities during the slowing down is consistent with the force balance model between the j × B force due to the external RMP and a viscous force. These results suggest that the slowing down of both locked-mode-like instabilities with finite external RMP occurs due to the j × B force driven by the external RMP., source:Y. Takemura et al 2021 Nucl. Fusion 61 026011, source:https://doi.org/10.1088/1741-4326/abc935, identifier:0000-0003-3754-897X

The aim of the present study is to perform a theoretical analysis of different strategies to stabilize energetic-ion-driven resistive interchange mode (EIC) in Large Helical Device (LHD) plasma. We use a reduced MHD for the thermal plasma coupled with a gyrofluid model for the energetic particles (EP) species. The hellically trapped EP component is introduced through a modification of the drift frequency to include their precessional drift. The stabilization trends of the 1/1 EIC observed experimentally with respect to the thermal plasma density and temperature are reproduced by the simulations, showing a reasonable agreement with the data. The LHD operation scenarios with stable 1/1 EIC are identified, leading to the stabilization of the 1/1 EIC if the thermal plasma density and temperature are above a given threshold. The 1/1 EIC are also stabilized if the rotational transform is modified in a way that the 1/1 rational surface is located further away than 0.9 times the normalized radius, or the magnetic shear in the plasma periphery is enhanced. Also, LHD discharges with large magnetic fields show a higher EIC destabilization threshold with respect to the thermal plasma density. If the perpendicular NBI deposition region is moved further inward than 0.875 times the normalized radius the 1/1 EIC are also stabilized. In addition, increasing the perpendicular NBI voltage such that the EP energy is higher than 30 keV stabilizes the 1/1 EIC. Moreover, deuterium plasmas show a higher stability threshold for the 1/1 EIC than hydrogen plasmas. The experimental data shows a larger time interval between EIC events as the power of the tangential NBI is increased providing that the perpendicular NBI power is at least 13 MW. This implies a stabilizing effect of the tangential NBI., source:J. Varela et al 2020 Nucl. Fusion 60 046013, source:https://doi.org/10.1088/1741-4326/ab7213, identifier:0000-0002-6114-0539

We investigate the penetration threshold of resonant magnetic perturbation (RMP) by the external coils in the Large Helical Device (LHD) for various plasma aspect ratio configurations. The qualitative dependence on the collisionality is opposite to that in a high plasma aspect configuration; this is a quite unique property first found in the LHD. We also investigate the threshold dependence on the ion species, and find that the threshold in deuterium discharges is much smaller than that in hydrogen discharges. In all cases the thresholds are higher as the poloidal rotation becomes faster, which shows that poloidal rotation is the dominant driver to the RMP shielding. This is qualitatively consistent with the torque balance model between the electromagnetic and poloidal viscous torques. In a configuration of the LHD, the dependence of the threshold on the density is qualitatively similar to that in Ohmic tokamak plasmas, but the beta dependence is opposite to that of tokamaks. The difference arises from the cause of the viscous torque., source:K. Y. Watanabe et al 2019 Nucl. Fusion 59 086049, source:https://doi.org/10.1088/1741-4326/ab2281, identifier:0000-0002-5653-5579