Seikichi Matsuoka

Extension of the high-ion-temperature regime in the Large Helical Device

High-ion-temperature (exceeding 5keV) hydrogen plasmas have been successfully produced in the Large Helical Device [Iiyoshi et al., Nucl. Fusion 39, 1245 (1999); Motojima et al., Nucl. Fusion 47, S668 (2007)] with the ion heat confinement improvement in the core region. The experimental ion heat diffusivity at the core region is found to be almost independent of the ion temperature, Ti (even decreasing as Ti increases). The neoclassical (NC) ripple transport is suppressed by the ambipolar radial electric field, Er (<0) predicted by NC transport fluxes. The temperature ratio, Ti∕Te, is one of the key parameters to reduce the NC ambipolar particle and heat fluxes. Thus, it is suggested that the selective ion heating (making Ti∕Te larger) is a plausible approach to further increase Ti. Spontaneous rotation is evaluated in these high-Ti plasmas, in which a co-directed component is recognized at the radial location with a large Ti gradient, in addition to the tokamak-like counter-directed component expected fo...

Neoclassical electron transport calculation by using delta f Monte Carlo method

High electron temperature plasmas with steep temperature gradient in the core are obtained in recent experiments in the Large Helical Device [A. Komori et al., Fusion Sci. Technol. 58, 1 (2010)]. Such plasmas are called core electron-root confinement (CERC) and have attracted much attention. In typical CERC plasmas, the radial electric field shows a transition phenomenon from a small negative value (ion root) to a large positive value (electron root) and the radial electric field in helical plasmas are determined dominantly by the ambipolar condition of neoclassical particle flux. To investigate such plasmas’ neoclassical transport precisely, the numerical neoclassical transport code, FORTEC-3D [S. Satake et al., J. Plasma Fusion Res. 1, 002 (2006)], which solves drift kinetic equation based on δf Monte Carlo method and has been applied for ion species so far, is extended to treat electron neoclassical transport. To check the validity of our new FORTEC-3D code, benchmark calculations are carried out with ...

Control of non-inductive current in Heliotron J

Non-inductive currents of electron cyclotron heated plasmas have been examined in the helical-axis heliotron device, Heliotron J. The bootstrap and EC currents were separated by comparing experiments with positive and negative magnetic field. The estimated bootstrap current was found to be affected by the magnetic field configuration. It increases with an increase in the bumpy component of the magnetic field spectrum, which agrees well with a neoclassical prediction calculated using the SPBSC code. The EC current driven by oblique launch with respect to the magnetic field strongly depends on the field configuration and the location of the EC power deposition. The EC current is enhanced when the EC power is deposited on the magnetic axis. The maximum EC current is IEC = ?4.6?kA and the current drive efficiency is ? = neRIp/PEC = 8.4 ? 1016?A?W?1?m?2. The flow direction of the EC current depends on the magnetic field ripple structure where the EC power is deposited.

Effects of magnetic drift tangential to magnetic surfaces on neoclassical transport in non-axisymmetric plasmas

In evaluating neoclassical transport by radially local simulations, the magnetic drift tangential to a flux surface is usually ignored in order to keep the phase-space volume conservation. In this paper, effect of the tangential magnetic drift on the local neoclassical transport is investigated. To retain the effect of the tangential magnetic drift in the local treatment of neoclassical transport, a new local formulation for the drift kinetic simulation is developed. The compressibility of the phase-space volume caused by the tangential magnetic drift is regarded as a source term for the drift kinetic equation, which is solved by using a two-weight δf Monte Carlo method for non-Hamiltonian system [G. Hu and J. A. Krommes, Phys. Plasmas 1, 863 (1994)]. It is demonstrated that the effect of the drift is negligible for the neoclassical transport in tokamaks. In non-axisymmetric systems, however, the tangential magnetic drift substantially changes the dependence of the neoclassical transport on the radial ele...

Investigation of ion and electron heat transport of high-Te ECH heated discharges in the large helical device

An analysis of the radial electric field and heat transport, both for ions and electrons, is presented for a high-

Neoclassical transport benchmark of global full-f gyrokinetic simulation in stellarator configurations

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Benchmark of the local drift-kinetic models for neoclassical transport simulation in helical plasmas

electron cyclotron heated (ECH) discharge on the large helical device (LHD). Transport analysis is done using the task3d transport suite utilizing experimentally measured profiles for both ions and electrons. Ion temperature and perpendicular flow profiles are measured using the recently installed x-ray imaging crystal spectrometer diagnostic (XICS), while electron temperature and density profiles are measured using Thomson scattering. The analysis also includes calculated ECH power deposition profiles as determined through the travis ray-tracing code. This is the first time on LHD that this type of integrated transport analysis with measured ion temperature profiles has been performed without NBI, allowing the heat transport properties of plasmas with only ECH heating to be more clearly examined. For this study, a plasma discharge is chosen which develops a high central electron temperature (