Synergy of turbulent and neoclassical transport through poloidal convective cells

Asahi, Yuichi*; Grandgirard, V.*; Sarazin, Y.*; Donnel, P.*; Garbet, X.*; Idomura, Yasuhiro; Dif-Pradalier, G.*; Latu, G.*

Plasma Physics and Controlled Fusion, 61(6), p.065015_1 - 065015_15, 2019/05

https://doi.org/10.1088/1361-6587/ab0972

The role of poloidal convective cells on transport processes is studied with the full-F gyrokinetic code GYSELA. For this purpose, we apply a numerical filter to convective cells and compare the simulation results with and without the filter. The energy flux driven by the magnetic drifts turns out to be reduced by a factor of about 2 once the numerical filter is applied. A careful analysis reveals that the frequency spectrum of the convective cells is well-correlated with that of the turbulent Reynolds stress tensor, giving credit to their turbulence-driven origin. The impact of convective cells can be interpreted as a synergy between turbulence and neoclassical dynamics.

The Precise energy spectra measurement of laser-accelerated MeV/n-class high-Z ions and protons using CR-39 detectors

Kanasaki, Masato; Jinno, Satoshi*; Sakaki, Hironao; Kondo, Kiminori; Oda, Keiji*; Yamauchi, Tomoya*; Fukuda, Yuji

Plasma Physics and Controlled Fusion, 58(3), p.034013_1 - 034013_6, 2016/03

https://doi.org/10.1088/0741-3335/58/3/034013

In order to understand the synergetic interplay between the Coulomb explosion of clusters and the background gas dynamics, we have conducted ion acceleration experiments using CO clusters (250 nm in dia.) embedded in background H gas with the J-KAREN laser (1 J, 40 fs, 10 contrast) at JAEA-KPSI. By a careful analysis of etch pit positions on CR-39 and their structures including the etch pit growth behavior analysis with the multi-step etching technique, energy spectra for protons from the background gas and carbon/oxygen ions from the clusters are obtained separately. The maximum energies of protons and carbon/oxygen ions are determined as 1.6 MeV and 1.1 MeV/u, respectively. Based on the experimental results, the acceleration mechanism of the background gas ions induced by Coulomb explosion of clusters is discussed with the help from numerical simulations which employ a particle-in-cell (PIC) method including relaxation and ionization processes of plasma particles.

Integrated tokamak modelling with the fast-ion Fokker-Planck solver adapted for transient analyses

Toma, Mitsunori; Hamamatsu, Kiyotaka; Hayashi, Nobuhiko; Honda, Mitsuru; Ide, Shunsuke

Plasma Physics and Controlled Fusion, 57(9), p.095007_1 - 095007_9, 2015/09

https://doi.org/10.1088/0741-3335/57/9/095007

Integrated tokamak modelling that enables the simulation of an entire discharge periodis indispensable for designing advanced tokamak plasmas. For this purpose, we extend the integrated code TOPICS to make it more suitable for transient analyses in the fast-ion part. The fast-ion Fokker-Planck solver is integrated into TOPICS at the same level as the bulk transport solver so that the time evolutions of the fast ion and the bulk plasma are consistent with each other as well as with the equilibrium magnetic field. The integrated code is applied to ramp-up simulations for JT-60SA and ITER to confirm its capability and effectiveness in transient analyses. In the integrated simulations, the coupled evolution of the fast ions, plasma profiles, and equilibrium magnetic fields are presented.

Simulation of plasma current ramp-up with reduced magnetic flux consumption in JT-60SA

Wakatsuki, Takuma; Suzuki, Takahiro; Hayashi, Nobuhiko; Shiraishi, Junya; Ide, Shunsuke; Takase, Yuichi*

Plasma Physics and Controlled Fusion, 57(6), p.065005_1 - 065005_12, 2015/06

https://doi.org/10.1088/0741-3335/57/6/065005

Projection imaging with directional electron and proton beams emitted from an ultrashort intense laser-driven thin foil target

Nishiuchi, Mamiko; Choi, I. W.*; Daido, Hiroyuki; Nakamura, Tatsufumi*; Pirozhkov, A. S.; Yogo, Akifumi*; Ogura, Koichi; Sagisaka, Akito; Orimo, Satoshi; Daito, Izuru*; et al.

Plasma Physics and Controlled Fusion, 57(2), p.025001_1 - 025001_9, 2015/02

https://doi.org/10.1088/0741-3335/57/2/025001

Projection images of a metal mesh produced by directional MeV electron beam together with directional proton beam, emitted simultaneously from a thin foil target irradiated by an ultrashort intense laser. The mesh patterns are projected to each detector by the electron beam and the proton beam originated from tiny virtual sources of 20 micron meter and 10 micron meter diameters, respectively. Based on the observed quality and magnification of the projection images, we estimate sizes and locations of the virtual sources for both beams and characterize their directionalities. To carry out physical interpretation of the directional electron beam qualitatively, we perform 2D particle-in-cell simulation which reproduces a directional escaping electron component, together with a non-directional dragged-back electron component, the latter mainly contributes to building a sheath electric field for proton acceleration.

The Effect of the electron temperature and current density profiles on the plasma current decay in JT-60U disruptions

Shibata, Yoshihide; Isayama, Akihiko; Miyamoto, Seiji*; Kawakami, Sho*; Watanabe, Kiyomasa*; Matsunaga, Go; Kawano, Yasunori; Lukash, V.*; Khayrutdinov, R.*; JT-60 Team

Plasma Physics and Controlled Fusion, 56(4), p.045008_1 - 045008_8, 2014/04

https://doi.org/10.1088/0741-3335/56/4/045008

In JT-60U disruption, the plasma current decay during the initial phase of current quench has been calculated by a disruption simulation code (DINA) using the measured electron temperature profile. In the case of fast plasma current decay, has a peaked profile just after thermal quench and the profile doesn't change significantly during the initial phase of current quench. On the other hand, in the case of the slow plasma current decay, the profile is border just after the thermal quench, and the profile shrinks. The results of DINA simulation show that plasma internal inductance increases during the initial phase of current quench, while plasma external inductance does not change in time. The increase of is caused by current diffusion toward the core plasma due to the decrease of in intermediate and edge regions. It is suggested that an additional heating in the plasma periphery region has the effect of slowing down plasma current decay.

Impact of plasma rotation on the linear physics of resistive wall modes in tokamaks

Aiba, Nobuyuki; Shiraishi, Junya; Hirota, Makoto

Plasma Physics and Controlled Fusion, 55(7), p.074002_1 - 074002_7, 2013/00

https://doi.org/10.1088/0741-3335/55/7/074002

The authors identified that plasma poloidal rotation sometimes plays an important role for ideal MHD stability due to changing the Doppler-shift frequency. As the result, the stability of edge localized MHD mode can depends on the direction of toroidal rotation; this dependence is qualitatively consistent with the experimental results observed in JT-60U. Plasma rotation is also responsible for the stability of resistive wall mode (RWM). In reversed shear plasmas, plasma rotation once stabilize this RWM but destabilize this again when rotation frequency reaches to certain frequency. This re-destabilization is thought to be related to the coupling between RWM and a stable MHD wave; this coupling is one of the destabilizing mechanisms discussed in previous theoretical papers. This re-destabilized RWM can become unstable in the plasma whose beta value is below no-wall beta limit.

Innovation on high-power long-pulse gyrotrons

Litak, A.*; Sakamoto, Keishi; Thumm, M.*

Plasma Physics and Controlled Fusion, 53(12), p.124002_1 - 124002_14, 2011/12

https://doi.org/10.1088/0741-3335/53/12/124002

Extreme field science

Bulanov, S. V.; Esirkepov, T. Z.; Hayashi, Yukio; Kando, Masaki; Kiriyama, Hiromitsu; Koga, J. K.; Kondo, Kiminori; Kotaki, Hideyuki; Pirozhkov, A. S.; Bulanov, S. S.*; et al.

Plasma Physics and Controlled Fusion, 53(12), p.124025_1 - 124025_13, 2011/12

https://doi.org/10.1088/0741-3335/53/12/124025

Linear response model of the vertical electromagnetic force on a vessel applicable to ITER and future tokamaks

Miyamoto, Seiji

Plasma Physics and Controlled Fusion, 53(8), p.082001_1 - 082001_7, 2011/08

https://doi.org/10.1088/0741-3335/53/8/082001

Vertical displacement events (VDEs) and a subsequent plasma disruption cause severe electromagnetic force on the vacuum vessel of axisymmetric magnetic confinement fusion devices like tokamaks and spherical tokamaks. This force is a dominant factor for the supporting system of the vacuum vessel and in-vessel components and a lot of efforts have been devoted to predict the possible force in future machines such as ITER. The eddy and halo currents induced in the vessel accompanying VDE and current quench complicate the analysis of the electromagnetic force and usually, computer simulations are required to employ for the analysis. So far, a database of vertical force for ITER has been created based on DINA simulation. However, no theory has been developed for systematic explanation of the simulation data. The problem of calculating vertical electromagnetic force on the vessel is reformulated to a linear response problem. First, it is shown that a burdensome task of calculating in-vessel halo and eddy currents is reduced to the calculation of the source term of the vertical force, or a force exerted on the plasma by poloidal field (PF) coils. The calculation is carried out without relying on the knowledge of currents in the vessel. The vertical force then emerges as a result of linear response, or electromagnetic shielding by the vessel. The model provides an analytical way of calculating vertical force. As an example of application, dependence of vertical force on current quench rate is derived analytically. The obtained formula well reproduces the simulation result of DINA.