Experimental investigations of castellated monoblock structures in TEXTOR

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Castellation will be used in divertor and first wall components to provide thermomechanical stability of ITER. Radioactive fuel may be stored in the gaps of castellated structures representing a safety issue for ITER.Tungsten castellated structures with different shapes were exposed in TEXTOR to investigate the impact of cell shaping on impurity transport and fuel deposition in the gaps. 2After exposure a significant intermixing of tungsten was detected in carbon deposits in the gaps reaching 70 at. % W in the deposition layer. This will provide difficulties in cleaning the gaps in ITER. Poloidal gaps of shaped cells contained a factor or 3 less deuterium than those of rectangular cells, the carbon deposition exhibited only marginal advantages of a new geometry. Poloidal and toroidal gaps contained comparable amount of C and D. Significant deposition at the bottom of gaps was measured which could only partly be reproduced by modeling.

Section: Deposition In Poloidal Gapssupporting

confidence: 89%

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

Litnovsky¹,

Wienhold

Philipps³

et al. 2009

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“…In TEXTOR a probe head with similar gap structure made of 10×10 mm molybdenum alloy (TZM) blocks with 0.5mm gap width and 10mm gap depth was exposed to the plasma boundary [9,10]. In this case the local B-field inclination angle to the surface was 20º.…”

Section: Comparison To Textor Experimentsmentioning

confidence: 99%

“…In DIII-D a heatable sample was exposed to a detached divertor plasma to study the dependence of the gap deposition as function of material temperature. The derived growth rates together with results from the similar experiments in TEXTOR [9,10] can be finally used to obtain an estimate for the growth rate of the ITER in-vessel T-inventory due to deposition inside the gaps of the first wall.…”

Section: Introductionmentioning

confidence: 99%

Formation of deuterium–carbon inventories in gaps of plasma facing components

Krieger

Jacob

Rudakov³

et al. 2007

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Plasma facing components for ITER will be manufactured as macro brush structures or with castellated surfaces. Material samples with gaps of similar geometry as intended for ITER were exposed to different plasma conditions in TEXTOR, DIII-D and ASDEX Upgrade. In all devices a decrease of both carbon and deuterium inventories at the side faces from the gap entrance into the gap with scale-lengths in the mm range is found. The fraction of D retained at the gap surfaces is in the range of 0.4-4% of the incident flux. Main parameters determining the retained D-fraction are the temperature of the respective surfaces and the carbon fraction in the incident flux. Extrapolation of tritium inventory growth rates to ITER dimensions assuming the measured retention fractions at T>200ºC and using a D/T-flux distribution with a carbon fraction of from B2/EIRENE simulations of an ITER H-mode discharge yields 1% ≈ 1 a contribution to the increase of the total in-vessel tritium inventory in the range of 0.5-5g T/discharge.

“…The design of castellated limiters used in the experiments is described in detail in [8]. The castellated structure consisted of 8 rows with 6 cells each with gaps of 0.5 mm between them.…”

Section: Exposure Of Castellated Limiters In the Sol Plasma Of Textormentioning

confidence: 99%

Carbon transport, deposition and fuel accumulation in castellated structures exposed in TEXTOR

Litnovsky¹,

Philipps²,

Kirschner³

et al. 2007

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In order to maintain the thermo-mechanical durability of ITER it is proposed to castellate the interior surface of the first wall and divertor by splitting them into small-size cells [W. Daener et al., Fusion Eng. Des. 61&62 (2002) 61]. A concern is the accumulation of fuel in the gaps of the castellation. In TEXTOR, molybdenum limiters were exposed in the scrape-off layer (SOL) plasma to assess fuel accumulation. The first limiter was exposed under deposition-dominated conditions. Carbon deposits were formed both on top surfaces and in the gaps. About 0.12% of the impinging D-fluence was found in the gaps. Another castellated limiter was exposed under erosion-dominated conditions. Deposited layers were found only on the plasma shadowed areas of the gaps. A significant amount of molybdenum from the limiter was found intermixed in the deposit. The gaps contained $0.03% of the impinging D-fluence. Modeling was performed to simulate carbon transport into the gaps.