<i>In situ</i> wavelength calibration system for the X-ray Imaging Crystal Spectrometer (XICS) on W7-X

Kring, J.; Pablant, N.; Langenberg, A.; Rice, J. E.; Delgado‐Aparicio, L.; Maurer, D.A.; Traverso, P.; Bitter, M.; Hill, K. W.; Reinke, M.L.

doi:10.1063/1.5038809

Cited by 14 publications

(5 citation statements)

References 7 publications

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“…The line-average plasma density is measured by a singlechannel interferometer [41], and the plasma density profile is measured by TS. The ion temperature profile in W7-X is measured by an x-ray imaging crystal spectrometer (XICS) diagnostic [42][43][44] and a charge exchange recombination spectroscopy (CXRS) diagnostic [45]. To enable CXRS T i measurements, short 10 ms beam blips (compared to τ E > 100 ms of neutral beam injection (NBI) heating) are used.…”

Section: Profile Preparationmentioning

confidence: 99%

Ion temperature clamping in Wendelstein 7-X electron cyclotron heated plasmas

et al. 2021

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The neoclassical transport optimization of the Wendelstein 7-X stellarator has not resulted in the predicted high energy confinement of gas fueled electron-cyclotron-resonance-heated (ECRH) plasmas as modelled in (Turkin et al 2011 Phys. Plasmas 18 022505) due to high levels of turbulent heat transport observed in the experiments. The electron-turbulent-heat transport appears non-stiff and is of the electron temperature gradient (ETG)/ion temperature gradient (ITG) type (Weir et al 2021 Nucl. Fusion 61 056001). As a result, the electron temperature T e can be varied freely from 1 keV-10 keV within the range of P ECRH = 1-7 MW, with electron density n e values from 0.1-1.5 × 10 20 m −3 . By contrast, in combination with the broad electron-to-ion energy-exchange heating profile in ECRH plasmas, ion-turbulent-heat transport leads to clamping of the central ion temperature at T i ∼ 1.5 keV ± 0.2 keV. In a dedicated ECRH power scan at a constant density of n e = 7 × 10 19 m −3 , an apparent 'negative ion temperature profile stiffness' was found in the central plasma for (r/a < 0.5), in which the normalized gradient ∇T i /T i decreases with increasing ion heat flux. The experiment was conducted in helium, which has a higher radiative density limit compared to hydrogen, allowing a broader power scan. This 'negative stiffness' is due to a strong exacerbation of turbulent transport with an increasing ratio of T e /T i in this electron-heated plasma. This finding is consistent with electrostatic microinstabilities, such as ITG-driven turbulence. Theoretical calculations made by both linear and nonlinear gyro-kinetic simulations performed by the GENE code in the W7-X three-dimensional geometry show a strong enhancement of turbulence with an increasing ratio of T e /T i . The exacerbation of turbulence with increasing T e /T i is also found in tokamaks and inherently enhances ion heat transport in electron-heated

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Section: Profile Preparationmentioning

confidence: 99%

Ion temperature clamping in Wendelstein 7-X electron cyclotron heated plasmas

et al. 2021

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“…Here, the plasma pressure profile is utilized by the form p ∝ (1 − s) α , where s is the normalized toroidal flux. Such form has an acceptable fit to experimental measurements derived from TS system and X-ray Imaging Crystal Spectrometer [54]. A good agreement can be accessed in the selected discharge if assuming α = 3 as shown in figure 3.…”

Section: Modeling Set-upmentioning

confidence: 67%

Modeling of plasma beta effects on the island divertor transport in the standard configuration of W7-X

Liang

Knieps

et al. 2023

Nucl. Fusion

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The influence of plasma beta effects on the edge plasma transport in the Wendelstein 7-X standard configuration is studied systematically by using EMC3-EIRENE combined with a 3D equilibrium code named HINT. The magnetic topology changes induced by plasma beta effects are significantly reflected in plasma transport behaviors and heat flux patterns on divertor targets. After validating the modeling strategy by comparisons with experimental data, the extended simulations for high performance plasmas show that the threshold separatrix density for accessing the power detachment is reduced in higher beta plasmas. Compared with the vacuum field case, the impurity radiation distributions with finite beta effects are modified in the magnetic island region. The divertor heat flux is distributed more evenly along the toroidal direction on the strike line at the vertical target. The strike line on the horizontal target moves towards the pumping gap with an increase in the plasma beta. In addition, the different pressure profiles with the same central beta also result in a modified heat flux pattern on the divertor targets.

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“…In figure 7 the inferred ion temperature profiles (blue lines + stars) are shown for two discharges (#20181009.034, #20180920.011) which were already described and used to fit density profiles in the previous section. The fitted profiles are compared to data from the CXRS system [21] (black dots) measuring carbon emission and a fit of x-ray imaging crystal spectrometer (XICS) data [16,23] (orange line). The XICS data is corrected by subtracting 200 eV at every radial point.…”

Section: Main Ion Temperature Profile Inferencementioning

confidence: 99%

Bayesian inference of electron density and ion temperature profiles from neutral beam and halo Balmer-α emission at Wendelstein 7-X

Bannmann,

Ford,

Hoefel

et al. 2024

Plasma Phys. Control. Fusion

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By employing Bayesian inference techniques, the full electron density profile from the plasma core to the edge of Wendelstein 7-X (W7-X) is inferred solely from neutral hydrogen beam and halo Balmer-α (Hα) emission data. The halo is a cloud of neutrals forming in the vicinity of the injected neutral beam due to multiple charge exchange (CX) reactions. W7-X is equipped with several neutral hydrogen beam heating sources and a Hα spectroscopy system that views these sources from different angles and penetration depths in the plasma. As the beam and halo emission form complex spectra for each spatial point that are non-linearly dependent on the plasma density profile and other parameters, a complete model from the neutral beam injection and halo formation through to the spectroscopic measurements is required. The model is used here to infer electron density profiles for a range of common W7-X plasma scenarios. The inferred profiles show good agreement with profiles determined by the Thomson scattering and interferometry diagnostics across a broad range of absolute densities without any changes to the input or fitting parameters. The time evolution of the density profile in a discharge with continuous core density peaking is successfully reconstructed, demonstrating sufficient spatial resolution to infer strongly shaped profiles. Furthermore, it is shown as a proof of concept that the model is also able to infer the main ion temperature profile using the same data set.

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In situ wavelength calibration system for the X-ray Imaging Crystal Spectrometer (XICS) on W7-X

Cited by 14 publications

References 7 publications

Ion temperature clamping in Wendelstein 7-X electron cyclotron heated plasmas

Ion temperature clamping in Wendelstein 7-X electron cyclotron heated plasmas

Modeling of plasma beta effects on the island divertor transport in the standard configuration of W7-X

Bayesian inference of electron density and ion temperature profiles from neutral beam and halo Balmer-α emission at Wendelstein 7-X

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