Inference of molecular divertor density from filtered camera analysis of molecularly induced Balmer line emission during detachment in JET L-mode plasmas

Karhunen, J.; Holm, A.; Lomanowski, B.; Solokha, V.; Aleiferis, S.; Carvalho, P.; Groth, M.; Lawson, K.; Meigs, A.; Shaw, A.

doi:10.1088/1748-0221/17/01/c01032

Cited by 5 publications

(13 citation statements)

References 17 publications

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“…Our work shows: 1) one cannot assume Dα is dominated by EIE without further information and; 2) if PMI is sufficiently strong, the ionisation region cannot be inferred from hydrogen Balmer emission spectroscopy alone as EIE and PMI cannot be distinguished. This is supported by results from TCV [15,14]; JET [42,43] and MAST-U, where it was shown that molecules contribute strongly to the Dα emission. Section 4.2 showed that tracking the D 2 Fulcher band emission may, instead, be a suitable proxy for the ionisation region (possibly in combination with atomic hydrogen spectroscopy), meritorious of further study.…”

Section: Mast-u (Density Scan)supporting

confidence: 66%

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: Mast-u (Density Scan)supporting

confidence: 66%

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

Verhaegh,

Lipschultz,

Harrison

et al. 2022

Preprint

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show abstract

“…Figures 6(c) and (d) suggest significantly lower molecularly induced contributions for D γ than presented above for D α . The estimated molecularly induced emission fraction remains primarily within 10%-20%, approaching the limits of the method for successfully recognizing low emission contributions, as discussed in [41]. The D γ emission is, instead, strongly dominated by the electron-ion recombination component, whose relative contribution increases rapidly to above 80% in figure 6(d) for T e,osp < 2.0 eV, when a strong increase in the D γ intensity is observed in figure 6(c).…”

Section: Evolution Of Purely Atomic and Molecularly Induced Dα And Dγ...mentioning

confidence: 72%

“…The estimates of the molecularly induced Balmer D α and D γ emission discussed in the previous section were used to experimentally infer the molecular divertor density within the Balmer emission regions with the methodology described in section 2.2. The analysis discussed here expands the results presented in [41] as demonstration of the method at the outer strike point-revisited here in section 5.2-to the divertor volume in 2D. The inferred molecular densities are also compared to the estimates of the electron and atomic divertor densities, obtained as solutions of the same optimization process.…”

Section: Experimental Inference Of Molecular Divertor Density During ...mentioning

confidence: 78%

Experimental distinction of the molecularly induced Balmer emission contribution and its application for inferring molecular divertor density with 2D filtered camera measurements during detachment in JET L-mode plasmas

Karhunen

Holm

Lomanowski

et al. 2022

Plasma Phys. Control. Fusion

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A previously presented model for generating 2D estimates of the divertor plasma conditions at JET from deuterium Balmer line intensity ratios, obtained from tomographic reconstructions of divertor camera images, was amended to consider also the Balmer emission arising from molecular processes. Utilizing the AMJUEL and H2VIRB atomic and molecular databases of EIRENE enabled also inference of the molecular divertor density from the distinguished molecularly induced emission. Analysis of a JET L-mode density scan suggests the molecularly induced emission accounting for up to 60-70% and 10-20% of the Balmer Dα and Dγ intensities, respectively, at the onset of detachment, while electron-ion recombination becomes increasingly dominant with deepening detachment. Similar observations were made by post-processing EDGE2D-EIRENE simulations, which indicated significant roles of molecular D2 + ions and vibrational excitation of the D2 molecules as precursors for the molecularly induced emission. The inferred molecular density at the outer strike point was found to increase monotonously with decreasing strike point temperature, reaching approximately 30-50% of the local electron density at nmol,osp = 1-2×1020 m-3 at Te,osp ≈ 0.7 eV. A further steep increase by a factor of 3-5 was observed with decrease of Te,osp to 0.5 eV. The observations are in qualitative and reasonable quantitative agreement with EDGE2D-EIRENE predictions of nmol,osp within the uncertainties of the experimental data.

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“…Quantitative evidence of the importance of plasmamolecular interactions in terms of spectroscopic interpretation as well as divertor physics is now available for TCV [3,21,22] as well as MAST-U (this work), with preliminary work also indicating the importance of these interactions in spectroscopic interpretations during deep detachment for JET [24][25][26]. As such plasma-molecular interactions are not fully included in plasma-edge modelling [22], further investigating such reactions is important for reducing the uncertainties in the extrapolation of current day devices to future reactors-particularly for reactor concepts with ADCs.…”

Section: This Papermentioning

confidence: 84%

“…These differences are related to (1) the higher divertor electron densities; (2) the lower levels of divertor molecular density; (3) the electron temperatures do not drop as low on TCV (before baffles) (see section appendix A). Performing more detailed analysis of plasma-atom/molecular interactions in other devices, such as JET [25,26], are ongoing and preliminary results also identify the importance of PMI emission.…”

Section: The Generality Of the Four Detachment Phases On Mast-umentioning

confidence: 99%

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

et al. 2022

View full text Add to dashboard Cite

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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Inference of molecular divertor density from filtered camera analysis of molecularly induced Balmer line emission during detachment in JET L-mode plasmas

Cited by 5 publications

References 17 publications

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

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

Experimental distinction of the molecularly induced Balmer emission contribution and its application for inferring molecular divertor density with 2D filtered camera measurements during detachment in JET L-mode plasmas

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

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