The role of hydrogen molecular effects on detachment in Magnum-PSI

Akkermans, Gijs; Classen, I. G. J.; Perillo, R.; Meiden, H.J. van der; Brezinsek, S.

doi:10.1063/5.0017714

Cited by 18 publications

(23 citation statements)

References 39 publications

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“…The plasma and neutral densities (n e and n n ) determine the reaction rate of those interactions. Finally, plasma dimensions and geometry determine the residence time of neutrals in the SOL, and therewith the total interaction potential, as has been shown in (modeling) experiments with closed divertor concepts [3], as well as target closure experiments on linear devices [4]. In a process called divertor detachment, p-n interaction gives rise to momentum and energy losses in the SOL, thus lowering the particle and heat loads on the divertor target surface [5,6].…”

Section: Introductionmentioning

confidence: 93%

“…A three-staged differential pumping scheme ensures a low background pressure in the target chamber [12], while maintaining electron densities n e 1.5 • 10 21 in steady state operation. Magnum-PSI is used for various research purposes, including PFC testing [13,14], PFC diagnostics development, detachment physics studies [15,16], exploration of novel PMI regimes [17,18] and more. To investigate near-surface p-n coupling and its effects on the wall loads, the TS and CTS diagnostics (section 2.1) were complemented by two surface diagnostics: an in-target Langmuir probe and a thermographic heat flux measurement (presented in sections 2.2.1 and 2.2.2, respectively).…”

Section: Experimental Work On Magnum-psimentioning

confidence: 99%

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Thermalized collisional pre-sheath detected in dense plasma with coherent and incoherent Thomson scattering

et al. 2021

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In the direct vicinity of plasma-facing surfaces, the incident plasma particles interact with surface-recombined neutrals. Remarkably high near-surface plasma pressure losses were observed in the high-flux linear plasma generator Magnum-PSI. Combining the incoherent and coherent Thomson scattering diagnostics, we directly measured particle, momentum and energy fluxes down to 3 mm from the plasma target surface. At the surface, the particle and total heat flux were also measured, using respectively an in-target Langmuir probe and thermographic methods. The near-surface momentum and energy losses scale with density, and amount to at least 50 % and 20 %, respectively, at ne = 8•10 20 m −3 . These losses are attributed to the efficient exchange of charge, momentum and energy between incident plasma and surface-recombined neutrals. In low-temperature plasmas with sufficient density, incident particles go through several cycles of interaction and surface deposition before leaving the plasma, thereby providing an effective alternative dissipation channel to the incident plasma. Parallel plasma parameter profiles exhibit a transition with increasing plasma density. In lowdensity conditions, the plasma temperature is constant and near-surface ion acceleration is observed, attributed to the ambipolar electric field. Conversely, deceleration and plasma cooling are observed in dense conditions. These results are explained by the combined effect of ionneutral friction and electron-ion thermal equilibration in the so-called thermalized collisional pre-sheath. The energy available for ambipolar acceleration is thus reduced, as well as the upstream flow velocity. In the ITER divertor, enhanced near-surface p-n interaction is expected as well, given the overlap in plasma conditions. Including these effects in finite-element scrape-off layer models requires a near-surface resolution smaller than the neutral mean free path. This amounts to 1 mm in Magnum-PSI, and possibly an order of magnitude smaller in ITER.

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Section: Introductionmentioning

confidence: 93%

Section: Experimental Work On Magnum-psimentioning

confidence: 99%

Thermalized collisional pre-sheath detected in dense plasma with coherent and incoherent Thomson scattering

et al. 2021

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“…Such techniques, however, have generally not been applied to tokamaks as they require complicated setups. But they could be potentially applied to linear devices, where they could be supplemented with spectroscopic techniques [73]. More complete sets of the fundamental data for the isotopologues are starting to become available [74], which can be used by collisional-radiative models [30,31] to provide data for deuterium and tritium.…”

Section: Energy and Power Losses Associated With Mar And Madmentioning

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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“…The Magnum-PSI plasma beam has approximate cylindrical symmetry about its axis 45 . This cylindrical symmetry is often assumed during spectroscopic studies of Magnum-PSI (and also of Pilot-PSI), with an Abel inversion used to obtain the local plasma properties from the observed lineintegrals 20,41,46 . In this work, we will make the same assumption.…”

Section: E Abel Inversionmentioning

confidence: 99%

2D measurements of plasma electron density using coherence imaging with a pixelated phase mask

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Silburn

Sharples

et al. 2021

Review of Scientific Instruments

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In this paper, the pixelated phase mask (PPM) method of interferometry is applied to coherence imaging (CI)—a passive, narrowband spectral imaging technique for diagnosing the edge and divertor regions of fusion plasma experiments. Compared to previous CI designs that use a linear phase mask, the PPM method allows for a higher possible spatial resolution. The PPM method is also observed to give a higher instrument contrast (analogous to a more narrow spectrometer instrument function). A single-delay PPM instrument is introduced as well as a multi-delay system that uses a combination of both pixelated and linear phase masks to encode the coherence of the observed radiation at four different interferometer delays simultaneously. The new methods are demonstrated with measurements of electron density ne, via Stark broadening of the Hγ emission line at 434.0 nm, made on the Magnum-PSI linear plasma experiment. A comparison of the Abel-inverted multi-delay CI measurements with Thomson scattering shows agreement across the 3 × 1019 < ne < 1 × 1021 m−3 range. For the single-delay CI results, agreement is found for ne > 1 × 1020 m−3 only. Accurate and independent interpretation of single-delay CI data at lower ne was not possible due to Doppler broadening and continuum emission.

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The role of hydrogen molecular effects on detachment in Magnum-PSI

Cited by 18 publications

References 39 publications

Thermalized collisional pre-sheath detected in dense plasma with coherent and incoherent Thomson scattering

Thermalized collisional pre-sheath detected in dense plasma with coherent and incoherent Thomson scattering

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

2D measurements of plasma electron density using coherence imaging with a pixelated phase mask

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