The inter-ELM tungsten erosion profile in DIII-D H-mode discharges and benchmarking with ERO+OEDGE modeling

Abrams, T.; Ding, Rui; Guo, H.Y.; Thomas, D.M.; Chrobak, C.; Rudakov, D. L.; McLean, A.G.; Unterberg, E.A.; Briesemeister, A.; Stangeby, P.C.; Elder, J.D.; Wampler, W.R.; Watkins, J. G.

doi:10.1088/1741-4326/aa66b2

Cited by 50 publications

(49 citation statements)

References 29 publications

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“…The fraction of Be ions was kept constant in this study whereas it might rise in addition during T plasma operation due to higher sputtering of Be from the main wall due to charge-exchange neutrals [9]. Please note, that the observations in D plasmas are consistent with recent studies in DIII-D [23] where the main impurity (carbon) fraction in the flux to the target plate dominates the W sputtering in the intra-ELM phase over the impinging deuterons.…”

Section: Physical Sputtering Of Tungstensupporting

confidence: 78%

Erosion, screening, and migration of tungsten in the JET divertor

et al. 2019

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The erosion of tungsten (W), induced by the bombardment of plasma and impurity particles, determines the lifetime of plasma-facing components as well as impacting on plasma performance by the influx of W into the confined region. The screening of W by the divertor and the transport of W in the plasma determines largely the W content in the plasma core, but the W source strength itself has a vital impact on this process. The JET tokamak experiment provides access to a large set of W erosion-determining parameters and permits a detailed description of the W source in the divertor closest to the ITER one: (i) effective sputtering yields and fluxes as function of impact energy of intrinsic (Be, C) and extrinsic (Ne, N) impurities as well as hydrogenic isotopes (H, D) are determined and predictions for the tritium (T) isotope are made. This includes the quantification of intra- and inter-edge localised mode (ELM) contributions to the total W source in H-mode plasmas which vary owing to the complex flux compositions and energy distributions in the corresponding phases. The sputtering threshold behaviour and the spectroscopic composition analysis provides an insight in the dominating species and plasma phases causing W erosion. (ii) The interplay between the net and gross W erosion source is discussed considering (prompt) re-deposition, thus, the immediate return of W ions back to the surface due to their large Larmor radius, and surface roughness, thus, the difference between smooth bulk-W and rough W-coating components used in the JET divertor. Both effects impact on the balance equation of local W erosion and deposition. (iii) Post-mortem analysis reveals the net erosion/deposition pattern and the W migration paths over long periods of plasma operation identifying the net W transport to remote areas. This W transport is related to the divertor plasma regime, e.g. attached operation with high impact energies of impinging particles or detached operation, as well as to the applied magnetic configuration in the divertor, e.g. close divertor with good geometrical screening of W or open divertor configuration with poor screening. JET equipped with the ITER-like wall (ILW) provided unique access to the net W erosion rate within a series of 151 subsequent H-mode discharges (magnetic field: T, plasma current: MA, auxiliary power MW) in one magnetic configuration accumulating 900 s of plasma with particle fluences in the range of 5– in the semi-detached inner and attached outer divertor leg. The comparison of W spectroscopy in the intra-ELM and inter-ELM phases with post-mortem analysis of W marker tiles provides a set of gross and net W erosion values at the outer target plate. ERO code simulations are applied to both divertor leg conditions and reproduce the erosion/deposition pattern as well as confirm the high experimentally observed prompt W re-deposition factors of more than 95% in the intra- and inter-ELM phase of the unseeded deuterium H-mode plasma. Conclusions to the expected divertor conditions in ITER as...

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Section: Physical Sputtering Of Tungstensupporting

confidence: 78%

Erosion, screening, and migration of tungsten in the JET divertor

et al. 2019

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“…Tungsten emission lines are among the least intense impurity UV lines present in measured DIII-D spectra, consistent with the low sputtering yield of tungsten [28]; yet, Tungsten emission is more intense compared to the background spectra in the CTH experiment than in DIII-D. Measured tungsten spectral lines in CTH are stronger, due to the greater solid angle of W emission as viewed by the CTH collection optics.…”

Section: Resultssupporting

confidence: 62%

Advances in neutral tungsten ultraviolet spectroscopy for the potential benefit to gross erosion diagnosis

Johnson¹,

Ennis²,

Loch³

et al. 2019

Plasma Phys. Control. Fusion

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A spectral survey of tungsten emission in the ultraviolet region has been completed in the DIII-D tokamak and the CTH torsatron to assess the potential benefit of UV emission for the diagnosis of gross W erosion. A total of 29 W I spectral lines are observed from the two experiments using survey spectrometers between 200-400 nm with level identifications provided based on a structure calculation for many of the excited states that produce strong emission lines. Of the 29 observed lines, 20 have not previously been reported in fusion relevant plasmas, including an intense line at 265.65 nm which could be important for benchmarking the frequently exploited line at 400.88 nm. Nearly all of the observed spectral lines decay down to one of the six lowest energy levels for neutral W, which are likely to be long-lived metastable states. The impact of metastable level populations on the W I emission spectrum and any erosion measurement utilizing a spectroscopic technique is potentially significant. Nevertheless, the high density of W I emission in the UV region allows for the possibly of determining the relative metastable fractions and plasma parameters local to the erosion region. Additionally, the lines observed in this work could be used to perform multiple independent gross erosion measurements, leading to more accurate diagnosis of gross tungsten erosion.

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“…The camera was operated in fast line-scan mode with framing rate up to 12 kHz thus able to capture heat flux evolution during ELMs. The inserts near DiMES were imaged with a WI-filtered (400.9 nm) DiMES-TV camera with framing rate 100 Hz and exposure time 10 ms. [13]. Filtered photo multipliers (filterscopes) with sampling rate 5×10 5 Hz have been installed to monitor each of the W rings (two nearby chords with ∅2 cm per ring) and provide background subtracted photon fluxes of neutral W line at 400.9 nm using a recently implemented technique [14].…”

Section: Introductionmentioning

confidence: 99%

Tungsten erosion by unipolar arcing in DIII-D

Bykov¹,

Chrobak²,

Abrams³

et al. 2017

Phys. Scr.

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Unipolar arcing was an important mechanism of metal surface erosion during the recently conducted Metal Rings Campaign in DIII-D when two toroidally continuous tile rings with 5 cm wide W-coated TZM inserts were installed in graphite tiles in the lower divertor, one on the floor and one on the shelf. Most of the arc damage occurred on the shelf ring. The total amount of W removed by arcing from the affected ∼4% of the shelf ring area was estimated ∼0.8×10 21 at., about half of the total amount of W eroded and redeposited outside the inserts (1.8±0.9)×10 21 at. The rings were exposed for a total of ∼480 discharges, an equivalent of plasma time on W surfaces (with Ip >0.5 MA) ∼10 3 s. Arcing was monitored in situ with WI (400.9 nm) filtered camera and photomultipliers and showed that: (i) arcing only occurred during ELMs and disruptions, (ii) arcing rate was much lower on the floor than on the shelf ring, and (iii) arcing had a low cut off power flux density about 2 MW/m 2. About half of arc tracks had large 10 • pitch angle and probably were produced during disruptions. Such tracks were only found on the shelf. Moderate toroidal variation of the arc track density and W erosion with nearly n=1 pattern has been measured.

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The inter-ELM tungsten erosion profile in DIII-D H-mode discharges and benchmarking with ERO+OEDGE modeling

Cited by 50 publications

References 29 publications

Erosion, screening, and migration of tungsten in the JET divertor

Erosion, screening, and migration of tungsten in the JET divertor

Advances in neutral tungsten ultraviolet spectroscopy for the potential benefit to gross erosion diagnosis

Tungsten erosion by unipolar arcing in DIII-D

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