Measurement of the 2D emission profiles of hydrogen and impurity ions in the TCV divertor

Perek, A.; Linehan, B.; Wensing, M.; Verhaegh, K.; Classen, I. G. J.; Duval, B. P.; Février, O.; Reimerdes, H.; Theiler, C.; Wijkamp, Tijs; Baar, M.R. de

doi:10.1016/j.nme.2020.100858

Cited by 21 publications

(40 citation statements)

References 31 publications

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“…However, the 6/5 Balmer line ratio plateaus between the EIR and PMI/EIE dominant levels after the initial increase (∼ 0.3), after which it increases to EIR dominant levels (∼ 0.45) levels at T e < 0.8 eV, which is different from the TCV case (figure 10 b). Therefore, the electron density may explain some, but not all of the difference between the MAST-U and TCV observations in [19,20,15,3,32].…”

Section: Understanding the Impact Of Plasma-molecule Interactions On ...mentioning

confidence: 95%

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: Understanding the Impact Of Plasma-molecule Interactions On ...mentioning

confidence: 95%

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

Verhaegh,

Lipschultz,

Harrison

et al. 2022

Preprint

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“…Additionally, the ion target flux This is different from the f ν (T e , T i ) used by SOLPS-ITER. However, more detailed analysis in [58] indicates that there may not be a strong deviation of f ν from a Boltzmann distribution ¶ Studies with filtered camera systems [59,60] have identified the measured D α emission region near the target extends further into the private flux region than predicted by plasma-edge simulations. Although this effect may explain underestimations in the simulated D α brightness, compared to the experiment, this cannot explain the relative lack of plasma-molecule interaction contributions in the simulation.…”

Section: Mar and D αmentioning

confidence: 99%

The role of plasma-molecule interactions on power and particle balance during detachment on the TCV tokamak

et al. 2021

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This paper shows experimental results from the TCV tokamak that indicate plasma-molecule interactions involving D + 2 and possibly D − play an important role as sinks of energy (through hydrogenic radiation as well as dissociation) and particles during divertor detachment if low target temperatures (< 3 eV) are achieved. Both molecular activated recombination (MAR) and ion source reduction due to a power limitation effect are shown to be important in reducing the ion target flux during a density ramp. In contrast, the electron-ion recombination (EIR) ion sink is too small to play an important role in reducing the ion target flux. MAR or EIR do not occur during N 2 seeding induced detachment as the target temperatures are not sufficiently low.The impact of D + 2 is shown to be underestimated in present (vibrationally unresolved) SOLPS-ITER simulations, which could result from an underestimated D 2 + D + → D + 2 + D rate. The converged SOLPS-ITER simulations are post-processed with alternative reaction rates, resulting in considerable contributions of D + 2 to particle and power losses as well as dissociation below the D 2 dissociation area. Those findings are in quantitative agreement with the experimental results.

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“…In addition, we have applied our synthetic testing procedure to a N 2 seeded scan (with intrinsic carbon impurities) (figure 13c, d) to have more capabilities of testing our analysis as the plasma fields are different between the fuelling and seeding scans [38]. In this case, we have not used the temperature exclusion constraint based on the CIII front introduced previously as, given the magnetic geometry of the MAST-U Super-X divertor, the CIII front cannot be comfortably tracked using line integrated spectroscopy and instead requires camera diagnostics, such as [39,40]. We observe that, generally, there is an agreement within uncertainty (68% confidence intervals are shown) between the parameters inferred from the synthetic diagnostic and those obtained directly.…”

Section: Synthetic Testing On Mast-u Solps Simulationsmentioning

confidence: 99%

“…¶ There is a very weak dependence on such rates for estimating the "MAR/MAI per Hα photon" ratio as this changes depending on whether H + 2 was created through molecular charge exchange or H 2 ionisation -see section 5.5 They are often easier to diagnose than the Fulcher band, given the high spectral resolution and high sensitivity often required for molecular band studies. Given that BaSMPI uses Balmer line measurements, which can be measured using 2D multispectral imaging diagnostics [40], its analysis could in principle be extended to a 2D analysis. For this, however, electron density estimates would be required, which could be obtained using Helium line spectroscopy [49], coherence imaging techniques (for Stark broadening) or Bayesian analysis techniques [50].…”

Section: Balmer Line Contributions From Plasma-molecule Interactions ...mentioning

confidence: 99%

A novel hydrogenic spectroscopic technique for inferring the role of plasma–molecule interaction on power and particle balance during detached conditions

Verhaegh

Lipschultz

Bowman

et al. 2021

Plasma Phys. Control. Fusion

136

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Detachment, an important mechanism for reducing target heat deposition, is achieved through reductions in power, particle and momentum; which are induced through plasma–atom and plasma–molecule interactions. Experimental research in how those reactions precisely contribute to detachment is limited. Both plasma–atom as well as plasma–molecule interactions can result in excited hydrogen atoms which emit atomic line emission. In this work, we investigate a new Balmer Spectroscopy technique for Plasma–Molecule Interaction—BaSPMI. This first disentangles the Balmer line emission from the various plasma–atom and plasma–molecule interactions and secondly quantifies their contributions to particle (ionisation and recombination) and power balance (radiative power losses). Its performance is verified using synthetic diagnostic techniques of both attached and detached TCV and MAST-U SOLPS-ITER simulations. We find that H 2 plasma chemistry involving H 2 + and/or H − can substantially elevate the Hα emission during detachment, which we show is an important precursor for Molecular Activated Recombination. An example illustration analysis of the full BaSPMI technique shows that the hydrogenic line series, even Lyα as well as the medium-n Balmer lines, can be significantly influenced by plasma–molecule interactions by tens ofpercent. That has important implications for using atomic hydrogen spectroscopy for diagnosing divertor plasmas.

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Measurement of the 2D emission profiles of hydrogen and impurity ions in the TCV divertor

Cited by 21 publications

References 31 publications

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

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

The role of plasma-molecule interactions on power and particle balance during detachment on the TCV tokamak

A novel hydrogenic spectroscopic technique for inferring the role of plasma–molecule interaction on power and particle balance during detached conditions

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