Development of an 11-channel multi wavelength imaging diagnostic for divertor plasmas in MAST Upgrade

Feng, X.; Calcines, A.; Sharples, R. M.; Lipschultz, B.; Perek, A.; Vijvers, W.A.J.; Harrison, James R.; Allcock, J. S.; Andrèbe, Y.; Duval, B.P.; Mumgaard, R.; Team, Mast-U; Team, EUROfusion Mst

doi:10.1063/5.0043533

Cited by 14 publications

(13 citation statements)

References 19 publications

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“…For a known n e , ∆L decreases with decreasing T e . If we assume T e = 0.2 eV (ADAS default temperature limit [28]), one would require a pathlength of 1.6 m near the target and 0.2 m near the divertor entrance at t = 600 ms. As ∆L is limited to 0.20-0.40 m physically (from a rough inversion of the MWI n = 9 Balmer line measurement [17]), this provides further evidence for a T e = 0.1 − 0.2 eV regime obtained from the Boltzmann fit.…”

Section: 31supporting

confidence: 51%

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Spectroscopic investigations of detachment on the MAST Upgrade Super-X divertor

Verhaegh,

Lipschultz,

Harrison

et al. 2022

Preprint

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We present the first analysis of the atomic and molecular processes at play during detachment in the MAST-U Super-X divertor using divertor spectroscopy data. Our analysis indicates detachment in the MAST-U Super-X divertor can be separated into four sequential phases: First, the ionisation region detaches from the target at detachment onset leaving a region of increased molecular densities downstream. The plasma interacts with these molecules, resulting in molecular ions (D + 2 and/or D − 2 → D + D − ) that further react with the plasma leading to Molecular Activated Recombination and Dissociation (MAR and MAD), which results in excited atoms and significant Balmer line emission. Second, the MAR region detaches from the target leaving a sub-eV temperature region downstream. Third, an onset of strong emission from electron-ion recombination (EIR) ensues. Finally, the electron density decays near the target, resulting in a density front moving upstream.The analysis in this paper indicates that plasma-molecule interactions have a larger impact than previously reported and play a critical role in the intensity and interpretation of hydrogen atomic line emission characteristics on MAST-U. Furthermore, we find that the Fulcher band emission profile in the divertor can be used as a proxy for the ionisation region and may also be employed as a plasma temperature diagnostic for improving the separation of hydrogenic emission arising from electron-impact excitation and that from plasma-molecular interactions.We provide evidences for the presence of low electron temperatures (< 0.5 eV) during detachment phases III-IV based on quantitative spectroscopy analysis, a Boltzmann

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Section: 31supporting

confidence: 51%

“…In addition to DMS, Multi-Wavelength Imaging (MWI) obtains images of spectrally filtered emission from the divertor [17,18]. MWI features up to 10 spectral filters to individual recording cameras, including the D 2 Fulcher band (595-605 nm) and the n = 3, 4, 5, 6, 7, 9 Balmer lines.…”

Section: Mast Upgrade Overviewmentioning

confidence: 99%

Spectroscopic investigations of detachment on the MAST Upgrade Super-X divertor

Verhaegh,

Lipschultz,

Harrison

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…If we assume T e = 0.2 eV (ADAS default temperature limit [41]), one would require a path-length of 1.6 m near the target and 0.2 m near the divertor entrance at t = 600 ms of # 45370. MAST-U features a multi-wavelength imaging (MWI) diagnostic [42], which can obtain spectrally filtered images of the divertor plasma, similar to MANTIS on TCV [43][44][45]. Inverting the MWI channel that hosts a filter for the n = 9 Balmer line, ΔL would limited to 0.20-0.40 m physically, this provides further evidence for a T e = 0.1-0.2 eV regime obtained from the Boltzmann fit.…”

Section: 31mentioning

confidence: 65%

Spectroscopic investigations of detachment on the MAST Upgrade Super-X divertor

et al. 2022

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We present the first analysis of the atomic and molecular processes at play during detachment in the MAST-U Super-X divertor using divertor spectroscopy data. Our analysis indicates detachment in the MAST-U Super-X divertor can be separated into four sequential phases: First, the ionisation region detaches from the target at detachment onset leaving a region of increased molecular densities downstream. The plasma interacts with these molecules, resulting in molecular ions (D2 + and/or D2 - -> D + D-) that further react with the plasma leading to Molecular Activated Recombination and Dissociation (MAR and MAD), which results in excited atoms and significant Balmer line emission. Second, the MAR region detaches from the target leaving a sub-eV temperature region downstream. Third, an onset of strong emission from electron-ion recombination (EIR) ensues. Finally, the electron density decays near the target, resulting in a density front moving upstream. The analysis in this paper indicates that plasma-molecule interactions have a larger impact than previously reported and play a critical role in the intensity and interpretation of hydrogen atomic line emission characteristics on MAST-U. Furthermore, we find that the Fulcher band emission profile in the divertor can be used as a proxy for the ionisation region and may also be employed as a plasma temperature diagnostic for improving the separation of hydrogenic emission arising from electron-impact excitation and that from plasma-molecular interactions. We provide evidences for the presence of low electron temperatures (<< 0.5 eV) during detachment phases III-IV based on quantitative spectroscopy analysis, a Boltzmann relation of the high-n Balmer line transitions together with an analysis of the brightness of high-n Balmer lines.

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“…The relatively recent implementation of high-resolution 10+ channel multi-spectral cameras for tokamak experiments [6] is giving rise to novel imaging applications at TCV [7,8] and other experiments [83]. The ability to simultaneously quantify the density of multiple atomic and molecular states in 2D will likely facilitate climacteric insights into boundary physics.…”

Section: Discussionmentioning

confidence: 99%

Validation of 2D Te and ne measurements made with Helium imaging spectroscopy in the volume of the TCV divertor

et al. 2023

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Multi-spectral imaging of helium atomic emission (HeMSI) has been used to create 2D poloidal maps of Te and ne in TCV’s divertor. To achieve these measurements, TCV’s MANTIS multispectral cameras simultaneously imaged four He I lines (2 singlet and 2 triplet) and a He II line (468nm) from passively present He and He+. The images, which were absolutely calibrated and covered the whole divertor region, were inverted through the assumption of toroidal symmetry to create emissivity profiles and, consequently, line-ratio profiles. A collisional-radiative model (CRM) was applied to the line-ratio profiles to produce 2D poloidal maps of Te and ne. The collisional-radiative modeling was accomplished with the Goto helium CRM code which accounts for electron-impact excitation and deexcitation (EIE), and electron-ion recombination (EIR) with He+. The HeMSI Te and ne measurements were compared with co-local Thomson scattering measurements. The two sets of measurements exhibited good agreement for ionizing plasmas: (5 eV ≤ Te ≤ 60 eV, and 2 × 1018 m-3 ≤ ne ≤ 3 × 1019 m-3) in the case of majority helium plasmas, and (10 eV ≤ Te ≤ 40 eV, 2 × 1018 m-3 ≤ ne ≤ 3 × 1019 m-3) in the case of majority deuterium plasmas. However, there were instances where HeMSI measurements diverged from Thomson scattering. When Te ≤ 10 eV in majority deuterium plasmas, HeMSI deduced inaccurately high values of Te. This disagreement cannot be rectified within the CRM’s EIE and EIR framework. Second, on sporadic occasions within the private flux region, HeMSI produced erroneously high measurements of ne. Multi-spectral imaging of Helium emission has been demonstrated to produce accurate 2D poloidal maps of Te and ne within the divertor of a tokamak for plasma conditions relevant to contemporary divertor studies.

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Development of an 11-channel multi wavelength imaging diagnostic for divertor plasmas in MAST Upgrade

Cited by 14 publications

References 19 publications

Spectroscopic investigations of detachment on the MAST Upgrade Super-X divertor

Spectroscopic investigations of detachment on the MAST Upgrade Super-X divertor

Spectroscopic investigations of detachment on the MAST Upgrade Super-X divertor

Validation of 2D Te and ne measurements made with Helium imaging spectroscopy in the volume of the TCV divertor

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