A Unique high natural background radiation area; Dose assessment and perspectives

Hosoda, Masahiro*; Nugraha, E. D.*; Akata, Naofumi*; Yamada, Ryohei; Tamakuma, Yuki*; Sasaki, Michiya*; Kelleher, K.*; Yoshinaga, Shinji*; Suzuki, Takahito*; Rattanapongs, C. P.*; et al.

Science of the Total Environment, 750, p.142346_1 - 142346_11, 2021/01

https://doi.org/10.1016/j.scitotenv.2020.142346

The biological effects of low dose-rate radiation exposures on humans remains unknown. In fact, the Japanese nation still struggles with this issue after the Fukushima Dai-ichi Nuclear Power Plant accident. Recently, we have found a unique area in Indonesia where naturally high radiation levels are present, resulting in chronic low dose-rate radiation exposures. We aimed to estimate the comprehensive dose due to internal and external exposures at the particularly high natural radiation area, and to discuss the enhancement mechanism of radon. A car-borne survey was conducted to estimate the external doses from terrestrial radiation. Indoor radon measurements were made in 47 dwellings over three to five months, covering the two typical seasons, to estimate the internal doses. Atmospheric radon gases were simultaneously collected at several heights to evaluate the vertical distribution. The absorbed dose rates in air in the study area vary widely between 50 nGy h and 1109 nGy h. Indoor radon concentrations ranged from 124 Bq m to 1015 Bq m. That is, the indoor radon concentrations measured exceed the reference levels of 100 Bq m recommended by the World Health Organization. Furthermore, the outdoor radon concentrations measured were comparable to the high indoor radon concentrations. The annual effective dose due to external and internal exposures in the study area was estimated to be 27 mSv using the median values. It was found that many residents are receiving radiation exposure from natural radionuclides over the dose limit for occupational exposure to radiation workers. This enhanced outdoor radon concentration might be as a result of the stable atmospheric conditions generated at an exceptionally low altitude. Our findings suggest that this area provides a unique opportunity to conduct an epidemiological study related to health effects due to chronic low dose-rate radiation exposure.

A Possible breakthrough of power handling by plasma shaping in tokamak

Kikuchi, Mitsuru; Fasoli, A.*; Takizuka, Tomonori*; Diamond, P. H.*; Medvedev, S.*; Wu, Y.*; Duan, X.*; Kishimoto, Yasuaki*; Hanada, Kazuaki*; Pueschel, M. J.*; et al.

Proceedings of 8th IAEA Technical Meeting on Steady State Operation of Magnetic Fusion Devices (CD-ROM), 20 Pages, 2015/05

The standard D shaped H-mode operation showed excellent plasma confinement ut has important issues of transient and steady state heat flux. To solbe this issues, we proposed new scenario using plasma shaping as one of possible scenario of future tokamak reactor.

MHD stability and control

Matsunaga, Go; Furukawa, Masaru*

Purazuma, Kaku Yugo Gakkai-Shi, 88(11), p.660 - 662, 2012/11

http://ci.nii.ac.jp/naid/110009554632

no abstracts in English

Mechanisms of plasma rotation effects on the stability of type-I edge-localized mode in tokamaks

Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Oyama, Naoyuki; Kojima, Atsushi; Tokuda, Shinji*; Yagi, Masatoshi

Nuclear Fusion, 51(7), p.073012_1 - 073012_9, 2011/07

https://doi.org/10.1088/0029-5515/51/7/073012

Mechanisms of plasma rotation on edge MHD stability is investigated numerically by introducing energies that are distinguished by physics. By comparing them, it is found that an edge localized MHD mode is destabilized by the difference between an eigenmode frequency and an equilibrium toroidal rotation frequency, which is induced by rotation shear. In addition, this destabilizing effect becomes effective in the shorter wavelength region. The effect of poloidal rotation on the edge MHD stability is also investigated. Under the assumption that the change of an equilibrium by poloidal rotation is negligible, it is identified numerically that poloidal rotation can have both the stabilizing effect and the destabilizing effect on the edge MHD stability, which depends on the direction of poloidal rotation. Numerical analysis demonstrates that these effects of plasma rotation in both toroidal and poloidal directions can play important roles on type-I ELM phenomena in JT-60U H-mode plasmas.

A Numerical matching technique for linear resistive magnetohydrodynamics modes

Furukawa, Masaru*; Tokuda, Shinji; Zheng, L. J.*

Physics of Plasmas, 17(5), p.052502_1 - 052502_15, 2010/05

https://doi.org/10.1063/1.3420244

Destabilization mechanism of edge localized MHD mode by a toroidal rotation in tokamaks

Aiba, Nobuyuki; Furukawa, Masaru*; Hirota, Makoto; Tokuda, Shinji

Nuclear Fusion, 50(4), p.045002_1 - 045002_13, 2010/04

https://doi.org/10.1088/0029-5515/50/4/045002

In this paper, we investigate numerically the destabilizing effect of a toroidal rotation on the edge localized MHD mode, which induces the large amplitude edge localized mode (ELM). As the results of this analysis, we reveal that the toroidal rotation with shear can destabilize this MHD mode, and the destabilization is caused by the difference between the plasma rotation frequency and the frequency of the unstable mode, which mainly affects the pressure-driven component of the unstable mode. This destabilizing effect becomes more effective as the wave length of the mode becomes shorter, but such a MHD mode with short wave length is also stabilized by the sheared toroidal rotation due to the Doppler-shift at each flux surfaces. We clarify that the stability of the edge localized MHD mode, whose wave length is typically intermediate, is determined by the balance between these stabilizing and destabilizing effects.

MINERVA; Ideal MHD stability code for toroidally rotating tokamak plasmas

Aiba, Nobuyuki; Tokuda, Shinji; Furukawa, Masaru*; Snyder, P. B.*; Chu, M. S.*

Computer Physics Communications, 180(8), p.1282 - 1304, 2009/08

https://doi.org/10.1016/j.cpc.2009.02.008

A new linear MHD stability code MINERVA is developed for investigating a toroidal rotation effect on the stability of ideal MHD modes in tokamak plasmas. This code solves the Frieman-Rotenberg equation as not only the generalized eigenvalue problem but also the initial value problem. The parallel computing method used in this code realizes the stability analysis of both long and short wavelength MHD modes in short time. The results of some benchmarking tests show the validity of this MINERVA code. The numerical study with MINERVA about the toroidal rotation effect on the edge MHD stability shows that the rotational shear destabilizes the long/intermediate wavelength modes but stabilizes the short wavelength edge localized MHD modes, though the rotation frequency destabilizes both the long and the short wavelength MHD modes.

Topological transition from accretion to ejection in a disk-jet system; Singular perturbation of the Hall effect in a weakly ionized plasma

Shiraishi, Junya; Yoshida, Zensho*; Furukawa, Masaru*

Astrophysical Journal, 697(1), p.100 - 105, 2009/03

https://doi.org/10.1088/0004-637X/697/1/100

A thin disk accompanied by spindle-like jet, created commonly near massive central objects, exhibits a topologically singular aspect when viewed from an ideal macroscopic theory. The accreting inflow and jet's outflow are "singular perturbation" on the ambient Keplerian rotation, which are generated by some non-ideal higher-order (in the order of derivatives) effect. The Hall effect can generate such a structure in a weakly ionized plasma of a protostellar disk. Numerical estimate of the characteristic length scale defined by the singular perturbation justifies the precedence of the Hall effect.

Effects of a toroidal rotation on the stability boundary of the MHD modes in the tokamak edge pedestal

Aiba, Nobuyuki; Tokuda, Shinji; Furukawa, Masaru*; Oyama, Naoyuki; Ozeki, Takahisa

Proceedings of 22nd IAEA Fusion Energy Conference (FEC 2008) (CD-ROM), 8 Pages, 2008/10

Effects of a toroidal rotation are investigated numerically on the stability of the MHD modes in the edge pedestal, which relate to the type-I edge-localized mode (ELM). A new linear MHD stability code MINERVA is developed for solving the Frieman-Rotenberg equation, which is the linear ideal MHD equation with flow. As the result of the stability analysis, it is revealed that the sheared toroidal rotation destabilizes the edge localized MHD modes. The change of the safety factor profile affects this destabilizing effect. This is because the rotation effect on the edge MHD stability becomes stronger as the toroidal mode number of the unstable MHD mode increases, and this toroidal mode number strongly depends on the safety factor profile.

Stabilization mechanism of ballooning modes by toroidal rotation shear in tokamaks

Furukawa, Masaru; Tokuda, Shinji

Nuclear Fusion, 45(5), p.377 - 383, 2005/05

https://doi.org/10.1088/0029-5515/45/5/008

A ballooning perturbation in a toroidally rotating tokamak is expanded by square-integrable eigenfunctions of an eigenvalue problem associated with ballooning modes in a static plasma. Especially a weight function is chosen such that the eigenvalue problem has only the discrete spectrum. The eigenvalues evolve in time owing to toroidal rotation shear, resulting in countably infinite number of crossings among them. The crossings cause energy transfer from an unstable mode to the infinite number of stable modes; such transfer works as the stabilization mechanism of the ballooning mode. A simple analytic formula is derived for estimating the toroidal rotation shear required to stabilize the ballooning mode.