Chanho Moon - Academia.edu (original) (raw)

Papers by Chanho Moon

Journal of Applied Physics, Mar 7, 2021

Fourier-rectangular function (FRF) transform [K. Yamasaki et al., J. Appl. Phys. 126, 043304 (201... more Fourier-rectangular function (FRF) transform [K. Yamasaki et al., J. Appl. Phys. 126, 043304 (2019)] is used to analyze the structure and dynamics of plasma with cylindrical symmetry. In this article, a new technique based on FRF transform is proposed to elucidate the polarization characteristics of azimuthal modes and fluctuations. The application results are shown for a two-dimensional tomography image of linear cylindrical plasma. The method successfully resolves the polarization characteristics of azimuthal modes and attributes the intermittent behavior of the m=1 mode to its polarization characteristics.

Plasma and Fusion Research, Jun 18, 2021

Physics of Plasmas, Sep 1, 2019

It is observed that a low-frequency (~2 kHz) density fluctuation is excited in a transition of th... more It is observed that a low-frequency (~2 kHz) density fluctuation is excited in a transition of the poloidal flow velocity (Vθ) in the edge magnetic stochastic region of the Large Helical Device (LHD) plasmas. Furthermore, it is found that the propagation velocity becomes approximately zero in the proximity of the appearance region of the low-frequency fluctuation by using the edge multi-channel microwave Doppler reflectometer system. In particular, the low-frequency fluctuation is considered to be transmitted in both directions (inward and outward) away from the excitation position of the fluctuation, which behaves as the precursor of a magnetic fluctuation burst. Afterward, the edge H α signal intensity is sharply increased.

Meeting abstracts of the Physical Society of Japan, Mar 1, 2010

Journal of Applied Physics, Jul 28, 2019

Japan Geoscience Union, Apr 7, 2014

Scientific Reports, Dec 12, 2022

Nuclear Fusion, Jul 30, 2015

APS Division of Plasma Physics Meeting Abstracts, Oct 1, 2011

ABSTRACT A high-frequency (˜5 MHz) instability is observed when an electron temperature gradient ... more ABSTRACT A high-frequency (˜5 MHz) instability is observed when an electron temperature gradient (ETG) perpendicular to magnetic field lines is formed in an electron cyclotron resonance (ECR) discharge plasma, which is consistent with an ETG mode. On the other hand, ExB velocity shears can be controlled independently of the ETG by changing the bias voltages of concentrically segmented electron emitters. As the result, it is found that the ETG mode amplitudes decrease with increasing the strength of the ExB velocity shears. In addition, the ETG mode is suppressed more effectively in the presence of an electron density gradient, which suggests that the density-gradient driven mode compensates the temperature-gradient driven mode. In conclusion, our experiment clearly demonstrates the suppression of the ETG mode, which is affected by the ExB velocity shears and the electron density gradient.

This article assesses current understanding of hysteresis in transport relations, and its impact ... more This article assesses current understanding of hysteresis in transport relations, and its impact on the field. The rapid changes of fluxes compared to slow changes of plasma parameters are overviewed for both core and edge plasmas. The modulation ECH experiment is explained, in which the heating power cycles on-and-off periodically, revealing hysteresis and fast changes in the gradient-flux relation. The key finding is that hystereses were observed simultaneously in both the the gradient-flux and gradient-fluctuation relations. Hysteresis with rapid timescale exists in the channels of energy, electron and impurity densities, and plausibly in momentum. Advanced methods of data analysis are explained. Transport hysteresis can be studied by observing the higher harmonics of temperature perturbation δT m in heating modulation experiments. The hysteresis introduces the term δT m , which depends on the harmonic number m in an algebraic manner (not exponential decay). Next, the causes of hysteresis and its fast timescale are discussed. The nonlocal-in-space coupling works here, but does not suffice. One mechanism for 'the heating heats turbulence' is that the external source S in phase space for heating has its fluctuation in turbulent plasma. This coupling can induce the direct input of heating power into fluctuations. The height of the jump in transport hysteresis is smaller for heavier hydrogen isotopes, and could be one of the origins of isotope effects on Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Review of Scientific Instruments, Apr 1, 2016

Review of Scientific Instruments, May 1, 2021

Heavy ion beam probe (HIBP) systems have been designed for the new tokamak, PLATO [A. Fujisawa, A... more Heavy ion beam probe (HIBP) systems have been designed for the new tokamak, PLATO [A. Fujisawa, AIP Conf. Proc. 1993, 020011 (2018)]. The designs have been completed, and the installations are in progress. Two HIBPs are being installed in toroidal sections 180° apart to investigate long-range correlations in the toroidal direction. Each HIBP consists of an injection beamline and a detection beamline as usual. Yet, one of the HIBPs is equipped with an additional detection beamline; the measurement positions of its two detection beamlines can be placed on almost the same magnetic surface yet at poloidal angles that differ by ∼180°. The use of three detection beamlines allows us to investigate spatial asymmetry and long-range correlations in both the toroidal and poloidal directions, simultaneously. The detected beam intensity is expected to be enough for turbulence measurements in almost the entire plasma region when the electron density is up to 1 × 1019 m−3 by selecting appropriate ion species for the probe beam. Each detector has three channels 10 mm apart, allowing measurement of local structures of micro-scale turbulence. Therefore, using the HIBPs on the PLATO tokamak will enable both local and global properties of plasma turbulence to be investigated, simultaneously.

Plasma and Fusion Research, Apr 14, 2020

The magnetic field dependence of a linear argon plasma is examined with a tomography system in PA... more The magnetic field dependence of a linear argon plasma is examined with a tomography system in PANTA. It is found that a plateau region exists around a particular region of magnetic field (∼600 G), below and above which the plasma changes the properties of emission and its fluctuations. A model is proposed to explain the observed dependence, and the comparison demonstrates that the dependence should be ascribed to the change in the Lamor motion inside the plasma production source using helicon wave and the plasma transport after the production.

Plasma and Fusion Research, 2021

Journal of Plasma and Fusion Research SERIES, Mar 8, 2010

Nuclear Fusion, 2022

We present a non-parametric inference of impurity transport coefficients by using charge exchange... more We present a non-parametric inference of impurity transport coefficients by using charge exchange recombination spectroscopy measurements of Ne X, Ne VIII, O VIII, and C VI lines. Due to their close atomic numbers, neon, oxygen and carbon impurity ions are assumed to have the same diffusion coefficient D and convection velocity v. Unlike conventional techniques that modulate or perturb the impurity contents, we employ a quasi-stationary plasma with static impurity profiles. Since the ratio of v to D only describes the equilibrated profile of the sum of all impurity charge states, steady-state measurements can still decouple D and v if different charge states are simultaneously observed. We have formulated a non-parametric analysis framework based on the Bayesian probability theory and conducted transport coefficient measurements for a Type III ELMy H-mode plasma at ASDEX Upgrade. The charge exchange reactions with the background neutrals, which are known to affect the impurity charg...

Plasma and Fusion Research, 2021

2011 XXXth URSI General Assembly and Scientific Symposium, 2011

Journal of the Physical Society of Japan, 2020

Emission intensity from plasmas is a complicated function of electron temperature T e and electro... more Emission intensity from plasmas is a complicated function of electron temperature T e and electron density n e. To understand the dependence of on T e and n e , an experimental comparison between tomography data (local of ArII) and Langmuir probe data (T e and n e) in a linear plasma device PANTA is presented in this paper. In the comparison, the local emission intensity is modeled as model / T e n 2 e , and the model is validated by calculating both cross-correlation function and least squares of residuals between the fluctuations of and model. The comparison reveals that the both methods provide α = 2.3-2.7, higher than 2 that of the exponent of n e. This result confirms that dependence of T e on is larger than that of n e when T e is low, as in PANTA.

Journal of Applied Physics, Mar 7, 2021

Fourier-rectangular function (FRF) transform [K. Yamasaki et al., J. Appl. Phys. 126, 043304 (201... more Fourier-rectangular function (FRF) transform [K. Yamasaki et al., J. Appl. Phys. 126, 043304 (2019)] is used to analyze the structure and dynamics of plasma with cylindrical symmetry. In this article, a new technique based on FRF transform is proposed to elucidate the polarization characteristics of azimuthal modes and fluctuations. The application results are shown for a two-dimensional tomography image of linear cylindrical plasma. The method successfully resolves the polarization characteristics of azimuthal modes and attributes the intermittent behavior of the m=1 mode to its polarization characteristics.

Plasma and Fusion Research, Jun 18, 2021

Physics of Plasmas, Sep 1, 2019

It is observed that a low-frequency (~2 kHz) density fluctuation is excited in a transition of th... more It is observed that a low-frequency (~2 kHz) density fluctuation is excited in a transition of the poloidal flow velocity (Vθ) in the edge magnetic stochastic region of the Large Helical Device (LHD) plasmas. Furthermore, it is found that the propagation velocity becomes approximately zero in the proximity of the appearance region of the low-frequency fluctuation by using the edge multi-channel microwave Doppler reflectometer system. In particular, the low-frequency fluctuation is considered to be transmitted in both directions (inward and outward) away from the excitation position of the fluctuation, which behaves as the precursor of a magnetic fluctuation burst. Afterward, the edge H α signal intensity is sharply increased.

Meeting abstracts of the Physical Society of Japan, Mar 1, 2010

Journal of Applied Physics, Jul 28, 2019

Japan Geoscience Union, Apr 7, 2014

Scientific Reports, Dec 12, 2022

Nuclear Fusion, Jul 30, 2015

APS Division of Plasma Physics Meeting Abstracts, Oct 1, 2011

ABSTRACT A high-frequency (˜5 MHz) instability is observed when an electron temperature gradient ... more ABSTRACT A high-frequency (˜5 MHz) instability is observed when an electron temperature gradient (ETG) perpendicular to magnetic field lines is formed in an electron cyclotron resonance (ECR) discharge plasma, which is consistent with an ETG mode. On the other hand, ExB velocity shears can be controlled independently of the ETG by changing the bias voltages of concentrically segmented electron emitters. As the result, it is found that the ETG mode amplitudes decrease with increasing the strength of the ExB velocity shears. In addition, the ETG mode is suppressed more effectively in the presence of an electron density gradient, which suggests that the density-gradient driven mode compensates the temperature-gradient driven mode. In conclusion, our experiment clearly demonstrates the suppression of the ETG mode, which is affected by the ExB velocity shears and the electron density gradient.

This article assesses current understanding of hysteresis in transport relations, and its impact ... more This article assesses current understanding of hysteresis in transport relations, and its impact on the field. The rapid changes of fluxes compared to slow changes of plasma parameters are overviewed for both core and edge plasmas. The modulation ECH experiment is explained, in which the heating power cycles on-and-off periodically, revealing hysteresis and fast changes in the gradient-flux relation. The key finding is that hystereses were observed simultaneously in both the the gradient-flux and gradient-fluctuation relations. Hysteresis with rapid timescale exists in the channels of energy, electron and impurity densities, and plausibly in momentum. Advanced methods of data analysis are explained. Transport hysteresis can be studied by observing the higher harmonics of temperature perturbation δT m in heating modulation experiments. The hysteresis introduces the term δT m , which depends on the harmonic number m in an algebraic manner (not exponential decay). Next, the causes of hysteresis and its fast timescale are discussed. The nonlocal-in-space coupling works here, but does not suffice. One mechanism for 'the heating heats turbulence' is that the external source S in phase space for heating has its fluctuation in turbulent plasma. This coupling can induce the direct input of heating power into fluctuations. The height of the jump in transport hysteresis is smaller for heavier hydrogen isotopes, and could be one of the origins of isotope effects on Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Review of Scientific Instruments, Apr 1, 2016

Review of Scientific Instruments, May 1, 2021

Heavy ion beam probe (HIBP) systems have been designed for the new tokamak, PLATO [A. Fujisawa, A... more Heavy ion beam probe (HIBP) systems have been designed for the new tokamak, PLATO [A. Fujisawa, AIP Conf. Proc. 1993, 020011 (2018)]. The designs have been completed, and the installations are in progress. Two HIBPs are being installed in toroidal sections 180° apart to investigate long-range correlations in the toroidal direction. Each HIBP consists of an injection beamline and a detection beamline as usual. Yet, one of the HIBPs is equipped with an additional detection beamline; the measurement positions of its two detection beamlines can be placed on almost the same magnetic surface yet at poloidal angles that differ by ∼180°. The use of three detection beamlines allows us to investigate spatial asymmetry and long-range correlations in both the toroidal and poloidal directions, simultaneously. The detected beam intensity is expected to be enough for turbulence measurements in almost the entire plasma region when the electron density is up to 1 × 1019 m−3 by selecting appropriate ion species for the probe beam. Each detector has three channels 10 mm apart, allowing measurement of local structures of micro-scale turbulence. Therefore, using the HIBPs on the PLATO tokamak will enable both local and global properties of plasma turbulence to be investigated, simultaneously.

Plasma and Fusion Research, Apr 14, 2020

The magnetic field dependence of a linear argon plasma is examined with a tomography system in PA... more The magnetic field dependence of a linear argon plasma is examined with a tomography system in PANTA. It is found that a plateau region exists around a particular region of magnetic field (∼600 G), below and above which the plasma changes the properties of emission and its fluctuations. A model is proposed to explain the observed dependence, and the comparison demonstrates that the dependence should be ascribed to the change in the Lamor motion inside the plasma production source using helicon wave and the plasma transport after the production.

Plasma and Fusion Research, 2021

Journal of Plasma and Fusion Research SERIES, Mar 8, 2010

Nuclear Fusion, 2022

We present a non-parametric inference of impurity transport coefficients by using charge exchange... more We present a non-parametric inference of impurity transport coefficients by using charge exchange recombination spectroscopy measurements of Ne X, Ne VIII, O VIII, and C VI lines. Due to their close atomic numbers, neon, oxygen and carbon impurity ions are assumed to have the same diffusion coefficient D and convection velocity v. Unlike conventional techniques that modulate or perturb the impurity contents, we employ a quasi-stationary plasma with static impurity profiles. Since the ratio of v to D only describes the equilibrated profile of the sum of all impurity charge states, steady-state measurements can still decouple D and v if different charge states are simultaneously observed. We have formulated a non-parametric analysis framework based on the Bayesian probability theory and conducted transport coefficient measurements for a Type III ELMy H-mode plasma at ASDEX Upgrade. The charge exchange reactions with the background neutrals, which are known to affect the impurity charg...

Plasma and Fusion Research, 2021

2011 XXXth URSI General Assembly and Scientific Symposium, 2011

Journal of the Physical Society of Japan, 2020

Emission intensity from plasmas is a complicated function of electron temperature T e and electro... more Emission intensity from plasmas is a complicated function of electron temperature T e and electron density n e. To understand the dependence of on T e and n e , an experimental comparison between tomography data (local of ArII) and Langmuir probe data (T e and n e) in a linear plasma device PANTA is presented in this paper. In the comparison, the local emission intensity is modeled as model / T e n 2 e , and the model is validated by calculating both cross-correlation function and least squares of residuals between the fluctuations of and model. The comparison reveals that the both methods provide α = 2.3-2.7, higher than 2 that of the exponent of n e. This result confirms that dependence of T e on is larger than that of n e when T e is low, as in PANTA.