Investigations of castellated structures for ITER: The effect of castellation shaping and alignment on fuel retention and impurity deposition in gaps

Litnovsky, A.; Wienhold, P.; Philipps, V.; Krieger, K.; Kirschner, A.; Matveev, D.; Borodin, D.; Sergienko, G.; Schmitz, O.; Kreter, A.; Samm, U.; Richter, Silvia; Breuer, U.; Team, Textor

doi:10.1016/j.jnucmat.2009.01.097

Cited by 32 publications

(21 citation statements)

References 8 publications

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“…Taking into account that recent experiments in DIII-D, Textor, ASDEX Upgrade, and JT-60-U [14,16,37] showed deposition profiles with 1/e decay lengths that are typically a few times the gap width, one can conclude from our experiments, that cleaning of remote areas with oxygen glow discharges can be successful at elevated temperatures but will be ineffective at room temperature as the surface loss probability of the species dominating the erosion process is too large. The optimal strategy to remove redeposited carbon films by oxygen glow discharges in future fusion devices would be to operate at the highest temperature possible.…”

Section: Discussionmentioning

confidence: 52%

“…Apart from deposition of thick layers on plasma-exposed surfaces [12,13] co-deposition in narrow gaps of castellated structures is a major concern [13][14][15][16]. Especially the side walls of gaps are expected to be the main deposition areas [12][13][14][15][16].…”

Section: Introductionmentioning

confidence: 99%

“…Especially the side walls of gaps are expected to be the main deposition areas [12][13][14][15][16]. Also deposition far away from the first wall in socalled remote locations may contribute significantly to the total fuel build-up (see [2] and references therein).…”

Section: Introductionmentioning

confidence: 99%

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Fuel removal from tile gaps with oxygen discharges: reactivity of neutrals

et al. 2009

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Carbon removal in so-called remote areas, where no energetic species can reach the surface, is investigated with low-temperature glow discharges in pure oxygen. Plasma-deposited amorphous hydrogenated carbon thin films are used as a model system for redeposited films. Erosion measurements are performed on flat substrates as well as on two different 3D test structures. One design consists of 19 mm deep gaps with widths ranging from 0.5 to 4 mm to simulate ITER tile gaps. A second design consists of a flat box-like structure where particles can enter only through a narrow slit. Measurements are performed for substrate temperatures ranging from 290 to 580 K. Erosion rates follow an Arrhenius-type dependence on substrate temperature with an effective activation energy of 0.25 eV. While at room temperature the surface loss probability of the dominant eroding species is 50 % it becomes smaller at elevated temperatures. At elevated temperatures the films are not only removed faster but simultaneously erosion penetrates deeper into the gaps.

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Section: Discussionmentioning

confidence: 52%

Section: Introductionmentioning

confidence: 99%

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Fuel removal from tile gaps with oxygen discharges: reactivity of neutrals

et al. 2009

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“…For the gap width of 1 mm, this corresponds to a plasma-wetted area of 0.05 mm in a poloidal gap (leading edge). From experiments [11] and modelling [12] it is known that toroidal gaps also can receive even larger fluxes of incoming particles and therefore may show large impurity re-deposition that is at least comparable to the poloidal gaps. Ion penetration into toroidal gaps can not be evaluated from simple geometrical considerations; therefore in this work toroidal gaps were not simulated.…”

Section: Model Assumptionsmentioning

confidence: 99%

Estimation of the contribution of gaps to tritium retention in the divertor of ITER

Matveev¹,

Kirschner²,

Schmid³

et al. 2014

Phys. Scr.

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Abstract. An estimation of the contribution of gaps to beryllium deposition and resulting tritium retention in the divertor of ITER is presented. Deposition of beryllium layers in gaps of the full tungsten divertor is simulated with the 3D-GAPS code. For gaps aligned along the poloidal direction, non-shaped and shaped solutions are compared. Plasma and impurity ion fluxes from [K. Schmid, Nucl. Fusion 48 (2008) 105004] are used as input. Ion penetration into gaps is considered to be geometrical along magnetic field lines. The effect of realistic ion penetration into gaps is discussed. In total, gaps in the divertor are estimated to contribute about 0.3 mgT/s to the overall tritium retention dominated by toroidal gaps, which are not shaped. This amount corresponds to about 7800 ITER discharges up to the safety limit of 1 kg in-vessel tritium; excluding, however, tritium release during wall baking and retention at plasma-wetted and remote areas.

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“…In the end of exposure, problems with plasma control caused plasma shifts towards the limiter and led to temperature excursions at the plasma-closest edge of the castellation up to 1500°C. Post-mortem surface and elemental analyses were made inside the gaps, on plasma-facing top surfaces and on the gap holder as described in [9]. Deposits with up to 200 nm thickness were observed at the bottom of gaps compared to up to 500 nm thick deposits on the side surfaces.…”

Section: Experiments In Textormentioning

confidence: 99%

Modelling of impurity deposition in gaps of castellated surfaces with the 3D-GAPS code

Matveev

Kirschner

Litnovsky

et al. 2010

Plasma Phys. Control. Fusion

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Abstract. The Monte-Carlo neutral transport code 3D-GAPS is described. The code models impurity transport and deposition in remote areas, such as gaps between cells of castellated plasma-facing surfaces. A step-by-step investigation of the interplay of different processes that may influence the deposition inside gaps, namely particle reflection, elastic neutral collisions, different particle sources, chemical erosion, and plasma penetration into gaps is presented. Examples of modelling results in application to the TEXTOR experiment with a castellated test limiter are provided. It is shown that only with the assumption of the presence of species with different reflection probabilities, simulated carbon deposition profiles agree with experimental observations for side surfaces of the gaps. These species can be attributed to different particle sources, e.g., carbon atoms and hydrocarbon radicals. Background carbon ions and atoms have low and moderate values of the reflection coefficient (R≤0.6), while some of hydrocarbon radicals produced by chemical erosion of redeposited carbon layers have high reflection probability (R≥0.9). Deposition at the bottom of the gaps can not be adequately reproduced unless extreme assumptions on particle sources and reflection properties are imposed. Elastic neutral collisions and ionization of neutrals escaping the gaps have no significant influence on the results. Nevertheless, Particlein-Cell simulations of plasma penetration into gaps are essential for estimating the incoming ion flux and lead to a better quantitative agreement with experimental observations.

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Investigations of castellated structures for ITER: The effect of castellation shaping and alignment on fuel retention and impurity deposition in gaps

Cited by 32 publications

References 8 publications

Fuel removal from tile gaps with oxygen discharges: reactivity of neutrals

Fuel removal from tile gaps with oxygen discharges: reactivity of neutrals

Estimation of the contribution of gaps to tritium retention in the divertor of ITER

Modelling of impurity deposition in gaps of castellated surfaces with the 3D-GAPS code

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