ゾーナルフロー研究の現状と展望 ４．運動論によるゾーナルフローの解析, ４．２ ゾーナルフローとGAM 振動

This article introduces the fundamental principles governing zonal flows for researchers who are engaged in experiments. The mechanism of the Geodesic Acoustic Mode (GAM) is first introduced for a simple tokamak having a circular cross section. The theoretical basis of which was described a rather long time ago. The theory is then extended to include helical systems based on the perspective that the geodesic curvature of the confining magneticfield plays an essential role. It is found that a short connection length in helical systems lends GAM oscillations different features from those in tokamaks. Special attention is paid to the low frequency range and a new branch is analyzed, which is referred to in this article as low frequency GAM. The zonal flow in the lowest frequency range is known as stationary zonal flow and known to have weak damping. Finally, an attempt is made to unify the theories of these two different frequency ranges

High Energy Particle Measurements during Long Discharge in LHD

The spatial resolved energy spectra can be observed during a long discharge of NBI plasma bycontinuously scanning the neutral particle analyzer. In these discharges, the plasmas are initiated by the ECH heating, after that NBI#2 (Co-injection) sustains the plasma during 40-60 seconds. The scanned pitch angle is from 44 degrees to 74 degrees. The injected neutral beam (hydrogen) energy of NBI#2 is only 130 keV because the original ion source polarity is negative. The shape of spectra is almost similar from 44 degrees to 53 degrees. However the spectra from 55 degrees are strongly varied. It reflects the injection pitch angle of the beam according to the simulation (53 degrees ot R* = 3.75 m in simulation). The beam keeps the pitch angle at incidence until the beam energy becomes to the energy, which the pitch angle scattering is occurred by the energy loss due to the electron collision. The low flux region can be observed around 10-15 keV, which is 15 times of the electron temperature. The energy region may be equal to the energy at which the pitch angle scattering is occurred. At the energy, the particle is scattered by the collision with the plasma ions and some of particles may run away from the plasma because they have a possibility to enter the loss cone. According to the simulation, the loss cone can be expected at the 10 keV with the small angular dependence. The depth of the loss cone is deep at the small pitch angle. The hollow in the spectrum may be concluded to be the loss cone as the tendency is almost agreed with the experimental result

Impurity emission characteristics of long pulse discharges in Large Helical Device

Line spectra from intrinsic impurity ions have been monitored during the three kinds of long-pulse discharges (ICH, ECH, NBI). Constant emission from the iron impurity shows no preferential accumulation of iron ion during the long-pulse operations. Stable Doppler ion temperature has been also measured from Fe XX, C V and C III spectra

Recent Results from LHD Experiment with Emphasis on Relation to Theory from Experimentalist’s View

he Large Helical Device (LHD) has been extending an operational regime of net-current free plasmas towardsthe fusion relevant condition with taking advantage of a net current-free heliotron concept and employing a superconducting coil system. Heating capability has exceeded 10 MW and the central ion and electron temperatureshave reached 7 and 10 keV, respectively. The maximum value of β and pulse length have been extended to 3.2% and 150 s, respectively. Many encouraging physical findings have been obtained. Topics from recent experiments, which should be emphasized from the aspect of theoretical approaches, are reviewed. Those are (1) Prominent features in the inward shifted configuration, i.e., mitigation of an ideal interchange mode in the configuration with magnetic hill, and confinement improvement due to suppression of both anomalous and neoclassical transport, (2) Demonstration ofbifurcation of radial electric field and associated formation of an internal transport barrier, and (3) Dynamics of magnetic islands and clarification of the role of separatrix

Analysis of Potential for Critical Metal Resource Constraints in the International Energy Agency’s Long-Term Low-Carbon Energy Scenarios

As environmental problems associated with energy systems become more serious, it is necessary to address them with consideration of their interconnections—for example, the energy-mineral nexus. Specifically, it is unclear whether long-term energy scenarios assuming the expansion of low carbon energy technology are sustainable in terms of resource constraints. However, there are few studies that comprehensively analyze the possibility of resource constraints in the process of introducing low carbon energy technology from a long-term perspective. Hence, to provide guidelines for technological development and policy-making toward realizing the low carbon society, this paper undertakes the following: (1) Estimation of the impact of the expansion of low carbon energy technology on future metal demand based, on the International Energy Agency (IEA)’s scenarios; (2) estimation of the potential effects of low carbon energy technology recycling on the future supply-demand balance; (3) identification of critical metals that require priority measures. Results indicated that the introduction of solar power and next-generation vehicles may be hindered by resource depletion. Among the metals examined, indium, tellurium, silver, lithium, nickel and platinum were identified as critical metals that require specific measures. As recycling can reduce primary demand by 20%~70% for low carbon energy technology, countermeasures including recycling need to be considered

Geodesic Acoustic Eigenmodes

The eigenmode of a geodesic acoustic mode in the presence of a temperature gradient is discussed. Eigenmodes are obtained and the characteristic wavelength scales as ρ2/3i L1/3 T (ρi: ion gyroradius, LT: temperature gradient scale length). The direction of propagation is discussed

A Calculation of the Distribution Function of ICRF Heated Plasma in LHD using a Bounce-Averaged Fokker-Planck Equation

Abstract High-energy ions produced by the ion cyclotron range of frequency (ICRF) heating were observed on the Large Helical Device (LHD). The dependence of the count number of high-energy particles on pitch-angle was studied using the time-of-flight neutral particle analyzer (TOF-NPA) in the LHD. The angle of the line-of-sight was scanned at five successive discharges sustained by ICRF heating only. A unique "rabbit-ear" structure with a large population of high-energy ions at a certain pitch-angle, was observed. A bounce-averaged Fokker-Planck equation was applied to the LHD plasma in the helical magnetic configuration in order to explain the structure of the measured distribution function. The calculation successfully reproduced the "rabbit-ear" structure