Stability of Externally Driven Magnetic Islands in a Helical Plasma

Influence of external resonant magnetic perturbation (RMP) on a helical plasma is numerically investigated, using a set of reduced magnetohydrodynamic equations. Coexistence of the resistive interchange mode and RMP is simulated. In nonlinear simulations, saturated magnetic islands by the RMP typically show two states: oscillating small islands and locked large islands. In the former state, rotation of magnetic islands by neoclassical transport-driven poloidal flows disturbs growth of islands. On the other hand, in the latter state, locking of poloidal flows due to the RMP and growth of islands occur simultaneously. It is found that the curvature driven current enhances magnetic reconnection, and width of the large islands overcomes that of vacuum islands

Theoretical Analysis of Transport Barriers in Helical Systems

lntroduction The Abstract A set of one-dimensional model equation in helical system is analyzed including the electric field bifurcation. The spatial and temporal evolutions of the temperature and the electric field are examined. A spatial structure which is related with the edge transport barrier is duscussed. A self-generated oscillation of the edge temperature and the heat flux loss takes place under the constant heat flux from the core. The oscillation occurs near the transition boundary. The transport barrier in the inner region is found in the high confinement state

Reduced models of turbulent transport in helical plasmas including effects of zonal flows and trapped electrons

Using transport models, the impacts of trapped electrons on zonal flows and turbulence in helical field configurations are studied. The effect of the trapped electrons on the characteristic quantities of the linear response for zonal flows is investigated for two different field configurations in the Large Helical Device. The turbulent potential fluctuation, zonal flow potential fluctuation and ion energy transport are quickly predicted by the reduced models for which the linear and nonlinear simulation results are used to determine dimensionless parameters related to turbulent saturation levels and typical zonal flow wavenumbers. The effects of zonal flows on the turbulent transport for the case of the kinetic electron response are much smaller than or comparable to those in an adiabatic electron condition for the two different field configurations. It is clarified that the effect of zonal flows on the turbulent transport due to the trapped electrons changes, depending on the field configurations

Improved prediction scheme for ion heat turbulent transport

A novel scheme to predict the turbulent transport of ion heat of magnetic confined plasmas is developed by combining mathematical optimization techniques employed in data analysis approaches and first-principle gyrokinetic simulations. Gyrokinetic simulation, as a first-principle approach, is a reliable way to predict turbulent transport. However, in terms of the flux-matching [Candy et al., Phys. Plasmas 16, 060704 (2009)], quantitative transport estimates by gyrokinetic simulations incur extremely heavy computational costs. In order to reduce the costs of quantitative transport prediction based on the gyrokinetic simulations, we develop a scheme with the aid of a reduced transport model. In the scheme, optimization techniques are applied to find relevant input parameters for nonlinear gyrokinetic simulations, which should be performed to obtain relevant transport fluxes and to optimize the reduced transport model for a target plasma. The developed scheme can reduce the numbers of the gyrokinetic simulations to perform the quantitative estimate of the turbulent transport levels and plasma profiles. Utilizing the scheme, the predictions for the turbulent transport can be realized by performing the first-principle simulations once for each radial position

Gyrokinetic simulations for turbulent transport of multi-ion-species plasmas in helical systems

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

Microinstabilities in hydrogen- and helium-dominated multi-ion-species plasmas in LHD

The ion scale microinstabilities in the large helical device (LHD) are investigated by the gyrokinetic simulations for the multi-ion-species plasmas including hydrogen, helium, and impurity ions. The observations in the LHD experiments show that the ion temperature increases with the decreases of the ratio of hydrogen density to helium density. It is found from the linear gyrokinetic simulations with the multi-ion-species and real-mass kinetic electrons in the LHD discharges that the growth rates of the ion scale microinstabilities are reduced for the helium-dominated multi-species plasma compared with the hydrogen-dominated one. In addition to the differences of the conditions including the temperature, the density profiles, and the temperature ratio between both plasmas, due to the dependence on the mass number and the electric charge of the mixed ion species, the mixing length estimates obtained from the linear simulations predicts smaller ion thermal diffusivity for the helium-dominated plasma than the hydrogen-dominated one in the hydrogen gyro-Bohm unit, which is consistent with the experimental results

Relaxation of Coaxial Nonneutral Magnetized Plasmas

Abstract A variational principle is applied to the relaxation of pure electron plasma in a strong axial magnetic field. The initial cylindrical shell structure of electrons can be unstable against Kelvin Helmholtz instability, and the plasma shape relaxes to its final state having a diffused profile. The shape of the plasma distribution in the final state is given based upon the anzats of the minimum enstrophy, and an experimentally-testable formula is obtained

Simulation studies on temperature profile stiffness in ITG turbulent transport of helical plasmas for flux-matching technique

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\u27s 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

Modeling of turbulent particle and heat transport in helical plasmas based on gyrokinetic analysis

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

The Gravitation of the Moon Plays Pivotal Roles in the Occurrence of the Acute Myocardial Infarction

Acute myocardial infarction (AMI) is a social burden. However, being able to predict AMI could lead to prevention. A previous study showed only the relation between the lunar phase and the occurrence of AMI, but the period it takes for the moon to orbit around the earth and the period of the lunar phase differ. This study investigated the effect of the gravitation of the moon on AMI. Data was comprised of 1369 consecutive patients with first AMI at 5 hospitals from October, 1984 to December, 1997. The universal gravitation of the moon was calculated and compared to the earth onset time of AMI. Universal gravitation of the moon was derived by G*m/d2 (G: universal gravitation constant, m: the mass of the moon, d: the distance between the center of the moon and the center of the earth). The relationship between m/d2 and the cases of AMI was determined. There was an increase in cases, when there is a distance of more than 399864 km from the center of the earth to the center of the moon. The gravitation of more than 399864 km was determined to be weaker gravitation. It is confirmed that the number of AMI patients significantly increases at weaker gravitation periods in this multicenter trial. In conclusion, these results suggest that the gravitation of the moon may have an influence on the occurrence of AMI