Development of a synthetic phase contrast imaging diagnostic

Rost, J. C.; Lin, L.; Porkoláb, M.

doi:10.1063/1.3435217

Cited by 20 publications

(19 citation statements)

References 23 publications

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“…In the following subsection, we examine the effect of the velocity gradient on PCI spectra with a synthetic PCI diagnostic (Coda 1997; Lin et al. 2009; Rost, Lin & Porkolab 2010; Tsujii et al. 2015).…”

Section: Measurementsmentioning

confidence: 99%

Phase contrast imaging measurements and numerical simulations of turbulent density fluctuations in gas-fuelled ECRH discharges in Wendelstein 7-X

et al. 2021

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The fundamental nature of turbulent density fluctuations in standard Wendelstein 7-X (W7-X) stellarator discharges is investigated experimentally via phase contrast imaging (PCI) in combination with gyrokinetic simulations with the code GENE. We find that density fluctuations are ion-temperature-gradient-driven and radially localised in the outer half of the plasma. It is shown that the line-integrated PCI measurements cover the right range of wavenumbers and a favourable toroidal and poloidal location to capture some of the strongest density fluctuations in W7-X. Due to the radial localisation of fluctuations, measured wavenumber–frequency spectra exhibit a dominant phase velocity, which can be related to the $\boldsymbol {E\times B}$ rotation velocity at the radial position of a well in the neoclassical radial electric field. The match is robust against variations of heating power and line-integrated density, which is partly due to the localisation of fluctuations and partly due to effects of the radial gradient in the $\boldsymbol {E\times B}$ velocity profile on the wavenumber–frequency spectrum. The latter effect is studied with a newly built synthetic PCI diagnostic and global gyrokinetic simulations with GENE-3D.

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Section: Measurementsmentioning

confidence: 99%

Phase contrast imaging measurements and numerical simulations of turbulent density fluctuations in gas-fuelled ECRH discharges in Wendelstein 7-X

et al. 2021

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“…These systems are based on the line integrated measurements without spatial resolution along the beam axis. The line integrated turbulence can be investigated by the quantitative comparison with numerical turbulence simulation by using synthetic diagnostic techniques [7,8]. In order to obtain spatial resolution along the beam axis, so-called magnetic shear techniques are applied.…”

Section: Introductionmentioning

confidence: 99%

Determination of absolute turbulence amplitude by CO₂ laser phase contrast imaging

et al. 2020

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Phase contrast imaging (PCI) has the important advantages of good sensitivity and applicability for the measurements of fluctuation and turbulence in magnetically confined plasma. However, the determination of the absolute amplitude of fluctuation is not well established. In this article, we propose to determine the absolute amplitude of fluctuation with calibration. The fluctuation measured by CO 2 laser PCI (CO 2 -PCI) was confirmed by simultaneous measurements by using a HeNe heterodyne interferometer (HeNe-HI). In the test experiments, CO 2 -PCI and HeNe-HI measured sound fields, which are produced by the audio speaker ( f = 6 ∼ 18 kHz, k = 0.09 ∼ 0.33 mm −1 ) and the piezoelectric transducer ( f = 72 kHz, k = 1.3 mm −1 ). At f = 13 ∼ 18 kHz, k = 0.24 ∼ 0.33 mm −1 , the differences between CO 2 -PCI and HeNe-HI were 20 ∼ 30%. At f = 72 kHz, k = 1.3 mm −1 , the difference was less than ∼ 10%. On the other hand, the difference between PCI and HI becomes larger at f < 13 kHz, k < 0.24 mm −1 . This is because in these regions some parts of the scattered and non-scattered radiation were not clearly separated inside and outside the groove of the phase plate. The procedure of the absolute value determination was applied to the detached plasma of LHD and compared with the measurement by using a CO 2 laser heterodyne interferometer (CO 2 -HI). The signal of CO 2 -HI at f > 20 kHz is almost at the same as the level of noise. On the other hand, the 2D-PCI signal is clearly higher than the level 1Corresponding author.

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“…Gyrokinetic analysis of these experiments indicates that the turbulence is localized to r/a = 0.5-0.8 and the cause of transport in other regions, in particular in the inner core of the plasma column, or the edge region, is still not understood. In previous presentations [10] we noted that U/C S up to 6 occurs in the central plasma at the lowest densities (where U is the ohmic electron drift speed J/em e and C S = (T e /m i ) 1/2 is the acoustic speed), and we speculated on the role of current driven drift wave turbulence. While in past theoretical studies transport due to such acoustic type drift wave turbulence was thought to be unimportant, more subtle phenomena, such as distortions of the electron distribution cannot be excluded as causes of electron drift wave turbulence and transport.…”

Section: Introductionmentioning

confidence: 99%

Transport and turbulence studies in the linear ohmic confinement regime in Alcator C-Mod

Porkoláb¹,

Dorris²,

Ennever³

et al. 2012

Plasma Phys. Control. Fusion

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Abstract. Transport in ohmically heated plasmas in Alcator C-Mod was studied in both the linear (LOC) and saturated (SOC) ohmic confinement regimes and the importance of turbulent transport in the region r/a = 0.5-0.8, was established. After extensive analysis with TGLF and GYRO, it is found that using an effective impurity ion species with Z i = 8, and moderately high Z eff (2.0-5.6), in the LOC regime electron transport becomes dominant due to TEM turbulence. The key ingredient in the present results is the observation that dilution of the main ion species (deuterium) by impurity species of moderate charge state reduces the dominant ITG turbulence, in contrast to the SOC regime with little, if any dilution. The turbulent spectrum measured with the Phase Contrast Imaging (PCI) diagnostic is in good agreement with predictions of a synthetic PCI diagnostic adopted to Global GYRO. The toroidal rotation in the low density LOC regime is in the co-current direction but as the density is raised, in the SOC regime the rotation reverses to the counter current drive direction. Recently we have measured the impurity content of the plasma and found an effective Z i of 9.

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Development of a synthetic phase contrast imaging diagnostic

Cited by 20 publications

References 23 publications

Phase contrast imaging measurements and numerical simulations of turbulent density fluctuations in gas-fuelled ECRH discharges in Wendelstein 7-X

Phase contrast imaging measurements and numerical simulations of turbulent density fluctuations in gas-fuelled ECRH discharges in Wendelstein 7-X

Determination of absolute turbulence amplitude by CO₂ laser phase contrast imaging

Transport and turbulence studies in the linear ohmic confinement regime in Alcator C-Mod

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Development of a synthetic phase contrast imaging diagnostic

Cited by 20 publications

References 23 publications

Phase contrast imaging measurements and numerical simulations of turbulent density fluctuations in gas-fuelled ECRH discharges in Wendelstein 7-X

Phase contrast imaging measurements and numerical simulations of turbulent density fluctuations in gas-fuelled ECRH discharges in Wendelstein 7-X

Determination of absolute turbulence amplitude by CO2 laser phase contrast imaging

Transport and turbulence studies in the linear ohmic confinement regime in Alcator C-Mod

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Determination of absolute turbulence amplitude by CO₂ laser phase contrast imaging