Estimation of 2D distributions of electron density and temperature in the JET divertor from tomographic reconstructions of deuterium Balmer line emission

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

doi:10.1016/j.nme.2020.100831

Cited by 7 publications

(32 citation statements)

References 31 publications

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“…Iε intensity ratios against the measured values with the help of equation ( 2). The inclusion of the f mol variable is an amendment to the original model presented in [19,20], in which the purely atomic ADAS representation without the molecularly induced term provided only a solution for n at .…”

Section: Iγmentioning

confidence: 99%

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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Section: Iγmentioning

confidence: 99%

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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“…Methodology for generating 2D estimates of the electron density, n e , electron temperature, T e , and atomic density, n at , in the JET divertor volume was introduced in [4,5], based on intensity ratios of reflection-corrected tomographic reconstructions [9][10][11][12] of divertor camera images of the Balmer D 𝛼 , D 𝛾 and D 𝜀 emissions. The estimates are provided as results of a Markov chain Monte Carlo [13,14] optimization model with the help of atomic data of the ADAS database [15] and constraints from line-integrated spectroscopic measurements of the divertor n e and T e [16][17][18].…”

Section: Estimating Molecularly Induced D 𝜶 and D 𝜸 Emissionmentioning

confidence: 99%

“…The ADAS representation, however, considers only emission arising from purely atomic processes as a sum of electron-impact excitation and recombination, ignoring thus the additional contribution from molecular processes. The method presented in [4,5] has been amended to consider molecular processes by treating the emission intensity, I p→q , of a given electronic transition between principal quantum states p and q as a sum of its purely atomic and molecularly induced components:…”

Section: Estimating Molecularly Induced D 𝜶 and D 𝜸 Emissionmentioning

confidence: 99%

“…In this work, a Monte Carlo method previously presented in [4,5] for estimating local divertor plasma conditions from filtered camera observations of Balmer emission has been amended to distinguish the molecularly induced contributions from the total emission intensities. The molecularly induced emission contributions have been further post-processed to provide estimates of the molecular divertor density.…”

Section: Introductionmentioning

confidence: 99%

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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

Karhunen¹,

Holm²,

Lomanowski³

et al. 2022

J. Inst.

Self Cite

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A previously presented Monte Carlo method for estimating local plasma conditions in 2D based on intensity ratios of deuterium Balmer D α , D γ and D ɛ lines was amended to consider also the D α and D γ emission contributions arising from molecular processes. The obtained estimates were used to infer the molecular divertor density with the help of the molecular databases of EIRENE. The method was benchmarked against EDGE2D-EIRENE simulations and observed to reproduce the molecularly induced emission fractions and the molecular divertor densities primarily within 25% of the references. Experimental analysis of a JET L-mode density scan suggested molecularly induced D α and D γ contributions of up to 60–70% and 20%, respectively, during the process of detachment. The independent estimates of the molecular divertor density inferred from the obtained molecularly induced D α and D γ intensities agree within uncertainties with each other. Both estimates show the molecular density increasing up to approximately 1.0–2.0 × 1020 m−3 at the outer strike point in deep detachment with its ratio to the local electron density agreeing with EDGE2D-EIRENE predictions within the scatter of the experimental data.

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“…In order to understand the dynamics of the detachment process and the physics of detachment in the MAST-U divertor, a Multi-Wavelength Imaging (MWI) diagnostic has recently been built to diagnose the emission front and infer recombination rates from Balmer line intensities 6,7 . The MWI will also measure 2D distributions of electron density and electron temperature in divertor plasmas through line intensity ratios of Deuterium Balmer lines 8 and helium singlet and triplet lines [9][10][11] . The inferred 2D map of plasma parameters, combined with localized measurements from Langmuir probes/Thomson scattering systems and 1D emission-weighted plasma profiles from spectroscopy, will provide crucial knowledge for the interpretation of observations.…”

Section: Introductionmentioning

confidence: 99%

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

Feng

Calcines

Sharples

et al. 2021

Review of Scientific Instruments

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Divertor detachment and alternative divertor magnetic geometries are predicted to be promising approaches to handle the power exhaust of future fusion devices. In order to understand the detachment process caused by volumetric losses in alternative divertor magnetic geometries, a Multi-Wavelength Imaging (MWI) diagnostic has recently been designed and built for the Mega Amp Spherical Tokamak Upgrade (MAST-U). The MWI diagnostic will simultaneously capture 11 spectrally filtered images of the visible light emitted from divertor plasmas and provide crucial knowledge for the interpretation of observations and modeling efforts. This manuscript presents the optical design, mechanical design, hardware and test results of an 11-channel MWI system with a field of view of 40 o . The optical design shows better than 5mm FWHM spatial resolution at the plasma on all 11 channels across the whole field of view. The spread of angle of incidence on the surface of each filter is also analyzed to inform the bandwidth specification of the interference filters. The results of the initial laboratory tests demonstrate that a spatial resolution of better than 5mm FWHM is achieved for all 11 channels, meeting the specifications required for accurate tomography.

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Estimation of 2D distributions of electron density and temperature in the JET divertor from tomographic reconstructions of deuterium Balmer line emission

Cited by 7 publications

References 31 publications

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

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

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

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

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