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A transition from an interchange mode to a non-resonant mode is found in the nonlinear magnetohydrodynamic simulation for the partial collapse in a large helical device (LHD) plasma with a net toroidal current. This transition can occur when the magnetic shear is weak and the rotational transform is close to unity in the core region. In this transition, the mode number of the dominant Fourier component is reduced. As a result of the nonlinear evolution, the (m, n) = (1, 1) component can be dominant, where m and n are the poloidal and the toroidal mode numbers, respectively. This transition is considered to be a candidate to explain the observation in the LHD experiments with the net toroidal current that show partial collapses are caused by the (1, 1) mode., source:Citation K. Ichiguchi et al 2021 Nucl. Fusion 61 126056, source:https://doi.org/10.1088/1741-4326/ac3292, identifier:0000-0002-7698-0223

Particle transport processes of impurity ions in a multi-ion-species plasma in the Large Helical Device are investigated by neoclassical transport simulations. While the quasi-linear gyrokinetic analyses indicate that the anomalous contribution of the impurity particle transport is radially inward-directed, it is found that the external momentum sources can cause the existence of the electron root with positive radial electric field and outward-directed neoclassical particle flux of the impurity ion., source:https://doi.org/10.1585/pfr.12.1203039, identifier:0000-0002-2459-2392

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 Large Helical Device experiments, independent low-order magnetic fluctuations due to the resistive interchange mode are commonly observed; investigating the characteristics of this instability is our ultimate goal. Two new methods for analyzing the single low-order instability in the stochastic region are developed. One method investigates it by constructing the initial single-mode perturbation. The other method investigates it by constructing a reference surface outside the last closed flux surface. The reference surface is necessary for constructing the coordinates that are used to extract the Fourier mode in the stochastic field line structure., source:https://doi.org/10.1585/pfr.8.2403157

In this study, the integrated transport analysis suite, TASK3D-a, was developed to enhance the physics understanding and accurate discussion of the Large Helical Device (LHD) experiment toward facilitating transport model validation. Steady-state and dynamic (transient) transport analyses of NBI (neutral-beam-injection)-heated LHD plasmas have been greatly facilitated by this suite. This will increase the predictability of the transport properties of LHD plasmas toward reactor-relevant regimes and reactor-scale plasmas., source:https://doi.org/10.1585/pfr.8.2403016, identifier:0000-0001-8856-1483

In a deuterium operation on the Large Helical Device, the measurement and control equipment placed in the torus hall must survive under an environment of radiation. To study the effects of gamma-ray irradiation on the equipment, an irradiation experiment is performed at the Cobalt-60 irradiation facility of Nagoya University. Transient and permanent effects on a personal computer, media converters, programmable logic controllers, isolation amplifiers, a web camera, optical flow meters, and water sealing gaskets are experimentally surveyed. Transient noise appears on the web camera. Offset of the signal increases with an increase of the integrated dose on the programmable logic controller. The DeviceNet module on the programmable logic controller is broken at the integrated dose of 72 Gy, which is the expected range of the integrated dose of the torus hall. The other equipment can survive under the gamma-ray field in the torus hall., source:Ogawa K, Nishitani T, Isobe M, Sato M, Yokota M, Hayashi H, Kobuchi T and Nishimura T 2017 Effects of gamma-ray irradiation on electronic and non-electronic equipment of Large Helical Device Plasma Sci. Technology 19 025601., source:https://doi.org/10.1088/2058-6272/19/2/025601, identifier:0000-0003-4555-1837