Toroidal flow measurements of impurity ions in QUEST ECH plasmas using multiple viewing chords emission spectroscopy

Yoneda, Nao; Shikama, T.; Hanada, K.; Mori, Shigeki; Onchi, Takumi; Kuroda, Kengoh; Hasuo, Masahiro; Ejiri, A.; Matsuzaki, K; Osawa, Yusuke; Peng, Yi; Kawamata, Yuya; Sakamoto, Shinji; Idei, H.; Ido, T.; Nakamura, K.; Nagashima, Yoshihiko; Ikezoe, Ryuya; Hasegawa, Makoto; Higashijima, A.; Nagata, T.; Shimabukuro, Shun

doi:10.1016/j.nme.2021.100905

Cited by 6 publications

(6 citation statements)

References 12 publications

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“…They are shown in purple with the poloidal cross-sectional views of the devices in figure 5. In QUEST, the viewing chords were aligned on the midplane, and the tangency radii of the viewing chords η are shown by the purple markers [26]. The diameters of the viewing chords were approximately 30 mm at the tangency plane.…”

Section: Spectroscopic Systemsmentioning

confidence: 99%

“…Lastly, the Abel inversion was applied to the fitted I A assuming the toroidal symmetry of the plasma, and the radial profiles of the emissivity were obtained as shown in figure 7(b). The error of the emissivity was estimated by the following four steps [26]: (I) generate 500 datasets by adding Gaussian noise with the estimated standard deviation of I A to the measured I A , (II) fit each dataset to a sigmoid function, (III) apply the Abel inversion to the fitted dataset, and (IV) calculate the mean and standard deviation of the derived emissivity at each radial position. The mean and standard deviation were plotted as the value and standard deviation of emissivity in figure 7(b).…”

Section: Evaluation Of Rotational Temperaturesmentioning

confidence: 99%

“…Figures 12(a) and (b) shows the profiles of n e and T e along l used for the calculation (lines), which were determined from their radial profiles measured by Thomson scattering (markers) in the range of R = 0.73-1.09 m. The n e profile was fitted to a linear function of l, while T e was approximated to be a constant because of the small dependence of the calculation results on them as described in section 2.2. The values for the other plasma parameters were determined based on experimental results [26] and are summarized in table 3. The calculation was performed at T wall = 370 and 468 K, the same conditions as the measurements, considering only the rotational excitation (Rot), and the initial values T Xv=0 rot (l = 0) were set at T wall .…”

Section: Estimation Of Plasma-facing Surface Temperaturementioning

confidence: 99%

“…In QUEST, 16 tangentially-viewing optical fibers with 0.25 mm core diameters were used with two achromatic lenses. The fibers were connected to a Czerny-Turner spectrometer (Acton Research, AM-510; 1 m focal length, F/8.7, and 1800 grooves mm −1 grating), and the spectra were recorded on a CCD camera (Andor Technology, DU440-BU2; 2048 × 512 pixels and 13.5 µm square pixels)[26]. In LTX-β, two radially-viewing optical fibers with 0.6 mm core diameter were used with reflective collimators.…”

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confidence: 99%

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Spectroscopic measurement of increases in hydrogen molecular rotational temperature with plasma-facing surface temperature and due to collisional-radiative processes in tokamaks

et al. 2023

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Spatially resolved rotational temperature of ground state hydrogen molecules desorbed from plasma-facing surface was measured in QUEST, LTX-β, and DIII-D tokamaks, and the increases of the rotational temperature with the surface temperature and due to collisional-radiative processes in the plasmas were evaluated. The increase due to collisional-radiative processes was calculated by solving rate equations considering electron and proton collisional excitation and deexcitation and spontaneous emission. The calculation results suggest a high sensitivity for the rotational temperature to electron and proton densities, but a negligible sensitivity to the electron, proton, and surface temperatures. In the three tokamaks with different plasma parameters and plasma facing surface materials, the spatial profile of the rotational temperature was estimated using Fulcher-α emission lines (600-608 nm). In QUEST, the spatial profile of the rotational temperature was estimated from spatially resolved spectra. In the other tokamaks, the rotational temperature was evaluated assuming a single point emission with a location determined from the Fulcher-α emission profile as measured with a filtered camera. In metal-walled devices QUEST and LTX-β, the rotational temperature increased with the surface temperature, and the calculated collisional-radiative increase is consistent with measured increase assuming that the rotational temperature at the surface is approximately 450 K higher than the surface temperature. In DIII-D with carbon walls, a larger collisional-radiative increase than the other tokamaks was observed because of the higher density leading to a large difference from the calculated increase compared to the other smaller tokamaks. Measurement of the Fulcher-α emission profile with higher spatial resolution in DIII-D may reduce the difference and reveal the effect of the surface temperature on the rotational temperature. These results shows the increases in the rotational temperature with the surface temperature and due to the collisional-radiative processes.

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Section: Spectroscopic Systemsmentioning

confidence: 99%

Section: Evaluation Of Rotational Temperaturesmentioning

confidence: 99%

Section: Estimation Of Plasma-facing Surface Temperaturementioning

confidence: 99%

mentioning

confidence: 99%

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Spectroscopic measurement of increases in hydrogen molecular rotational temperature with plasma-facing surface temperature and due to collisional-radiative processes in tokamaks

et al. 2023

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“…Then, by ramping up the plasma current, an ST plasma sustained only with ECH is formed [2,4,6]. Among the characteristics of the initial ST plasma is a large variation in ion toroidal velocity in the range of 0-20 km/s with the size and position of the last closed flux surface (LCFS) [7]. Since this characteristic could be used for the active control of the flow profile, we intended to further investigate the driving and damping mechanisms of the flow.…”

Section: Introductionmentioning

confidence: 99%

Spectroscopic Measurement of Hydrogen Atom Density in a Plasma Produced with 28 GHz ECH in QUEST

Mori

Shikama

Hanada

et al. 2020

Atoms

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The spatial distribution of the hydrogen atom density was evaluated in a spherical tokamak (ST) plasma sustained only with 28 GHz electron cyclotron heating (ECH). The radially resolved Hδ emissivity was measured using multiple viewing chord spectroscopy and Abel inversion. A collisional-radiative (CR) model analysis of the emissivity resulted in a ground-state hydrogen atom density of 1015–1016 m−3 and an ionization degree of 1–0.85 in the plasma.

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High-fidelity inference of local impurity profiles in C-2W using Bayesian tomography

Nations

Romero

Gupta

et al. 2022

Review of Scientific Instruments

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In C-2W (also called “Norman”) [1], beam-driven field reversed configuration plasmas embedded in a magnetic mirror are produced and sustained in a steady state. A multi-chord passive Doppler spectroscopy diagnostic provides line-integrated impurity emission measurements near the center plane of the confinement vessel with fast time resolution. The high degree of plasma non-uniformity across optical sightlines can preclude direct fitting of the measured line-integrated spectra. To overcome this challenge, local impurity profiles are inferred using Bayesian tomography, a superior analysis technique based on a complete forward model of the diagnostic. The measured emission of O4+ triplet lines near 278.4 nm is modeled assuming two independent populations: thermal and beam ions. Gaussian processes are used to generate and infer local profiles. The inference incorporates details of the geometrical arrangement of the diagnostic, instrument function, intensity calibration, and a noise model. Markov chain Monte Carlo (MCMC) sampling of the posterior distribution of solutions provides high-fidelity uncertainty estimates. The reconstructed O4+ impurity profiles are consistent with data from other diagnostics and show good agreement with expected physics based on previously developed models of biasing circuit and impurity transport.

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Toroidal flow measurements of impurity ions in QUEST ECH plasmas using multiple viewing chords emission spectroscopy

Cited by 6 publications

References 12 publications

Spectroscopic measurement of increases in hydrogen molecular rotational temperature with plasma-facing surface temperature and due to collisional-radiative processes in tokamaks

Spectroscopic measurement of increases in hydrogen molecular rotational temperature with plasma-facing surface temperature and due to collisional-radiative processes in tokamaks

Spectroscopic Measurement of Hydrogen Atom Density in a Plasma Produced with 28 GHz ECH in QUEST

High-fidelity inference of local impurity profiles in C-2W using Bayesian tomography

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