Dynamics of erosion and deposition in tokamaks

Kreter, A.; Brezinsek, S.; Coad, J. P.; Esser, H. G.; Fundamenski, W.; Philipps, V.; Pitts, R.A.; Rohde, V.; Tanabe, T.; Widdowson, A.; Contributors, Jet

doi:10.1016/j.jnucmat.2009.01.041

Cited by 35 publications

(30 citation statements)

References 37 publications

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“…located at 0 cm) in the divertor agree qualitatively with the deposition pattern observed on the sensors of quartz microbalance (QMB) devices installed in the vicinity of the mirrors: most significant deposition in the inner divertor, less deposition in the outer leg [10,11]. Only limited comparison can be made because the QMB crystals were exposed to selected discharges, whereas the mirrors were facing plasma continuously during all operation scenarios.…”

Section: Images Insupporting

confidence: 63%

An overview of a comprehensive First Mirror Test for ITER at JET

Rubel

Temmerman

Sundelin

et al. 2009

Journal of Nuclear Materials

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a b s t r a c tThe test was performed with 32 stainless steel and molybdenum mirrors placed in pan-pipe shaped cassettes and exposed in JET in the divertor and on the main chamber wall for 127 000 s including 97 000 s of X-point operation. Surface composition and total reflectivity were determined afterwards. All mirrors from the divertor were coated with deuterated carbon deposits causing the reflectivity loss by a factor of 6-10 in the visible range. Flaking and exfoliation of deposits were observed in some cases. On the main chamber wall the deposition occurred mainly on mirrors located deep in cassette channels, whereas mirrors close to the channels entrances were free from deposits and retained fair reflectivity ($90% of initial value) especially in the infra-red range. No significant differences in behaviour of steel and molybdenum were noted. The need for development of methods for mirror cleaning and/or protection in a reactor-class device is addressed.

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Section: Images Insupporting

confidence: 63%

An overview of a comprehensive First Mirror Test for ITER at JET

Rubel

Temmerman

Sundelin

et al. 2009

Journal of Nuclear Materials

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“…In the reference experiment, denoted Ex fwd , 13 CH 4 was injected from two poloidal locations into the SOL. In the second experiment, denoted Ex src , only the upper poloidal location was used, and the strike point was shifted 3 cm upwards, see figure 1. This means that the puffing was made into a different location in the SOL plasma compared to the two injections in Ex fwd .…”

Section: Experimental Results From Local 13 C Injection Experiments Imentioning

confidence: 99%

“…These impurities may become transported into the core, where they dilute and cool the fuel, or migrate onto other wall segments or remote areas, changing the surface material composition or leading to dust accumulation. Conversely, material eroded from the main chamber wall can also accumulate in the outer divertor, depending on the migration properties of impurities [1,2]. The consequences may be critical for the operation of future fusion devices with high duty cycle, for which reason material selection has been one of the key design issues for ITER [3], and will be even more crucial for the design of a fusion reactor [2].…”

Section: Introductionmentioning

confidence: 99%

Outer divertor of ASDEX Upgrade in low-density L-mode discharges in forward and reversed magnetic field: II. Analysis of local impurity migration

et al. 2012

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Abstract. Part I presented a detailed analysis of outer divertor plasma conditions in low-density L-mode discharges in ASDEX Upgrade. In this paper, we analyse the local migration of carbon that originates from 13 CH 4 injected into these plasmas from the vertical outer target. Notable changes are observed in the local carbon deposition patterns when reversing the magnetic field in the experiments. Kinetic impurity-following simulations are performed using the 3D ERO code package with 2D background plasma solutions calculated with the SOLPS5.0 code package. The modelling shows that the measured changes are due to the changes in plasma collisionality, dissociation and ionization rates, and E × B drift of the impurities. These conditions affect the direction and rate of impurity migration inside and out of the divertor, having wider consequences on the global migration of impurities in a divertor tokamak. It is further shown, that the migration pathways are largely determined by carbon ions and, hence, relevant for impurities in general. Neutral carbon and hydrocarbons are deposited only in the near vicinity of the injection, where they affect the local re-deposition efficiency. In this limited region, a perturbation of the local plasma conditions by the methane puff appears likely, yielding a significant uncertainty for interpreting the deposition efficiencies. The local deposition is largely influenced by the magnetic presheath electric field, the structure of which is the main uncertainty in the SOLPS5.0-ERO simulations.

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“…This small value is not proportional to the exposure time. One may deduce that this could be attributed to (i) quite frequent flaking and peeling-off of the carbon layers deposited on the mirrors in the divertor, (ii) the dynamic character of erosion and deposition in the divertor region, as discussed in [17].…”

Section: Surface Composition Of the Exposed Mirrormentioning

confidence: 99%

Overview of the second stage in the comprehensive mirrors test in JET

et al. 2011

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The first mirror test for ITER in JET with carbon walls has been completed. Thirty polycrystalline Mo mirrors including four coated with a 1 µm rhodium (Rh) film were exposed to plasma in the divertor region and in the main chamber. The mirrors were installed in eight cassettes of pan-pipe shape. The reflectivity of all mirrors exposed in the divertor has been degraded by 80-90% because of the formation of thick (>20 µm) flaking co-deposits on surfaces. Only small reflectivity losses (5-10%) occurred on mirrors located at the channel mouth of the cassettes from the main chamber wall. This is due to the in situ removal of deposited species by charge exchange neutrals. Deuterium, 12 C and 9 Be are the main isotopes detected on surfaces, but other isotopes ( 13 C) are also found in some locations, thus indicating differences in the material migration. Rhodium coatings with an initial reflectivity that is 30% better than that of pure Mo survived the test without detachment, but their resultant reflectivity was the same as that of the exposed Mo surfaces.

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Dynamics of erosion and deposition in tokamaks

Cited by 35 publications

References 37 publications

An overview of a comprehensive First Mirror Test for ITER at JET

An overview of a comprehensive First Mirror Test for ITER at JET

Outer divertor of ASDEX Upgrade in low-density L-mode discharges in forward and reversed magnetic field: II. Analysis of local impurity migration

Overview of the second stage in the comprehensive mirrors test in JET

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