Abstract
Beryllium-seeded deuterium plasma is used in PISCES-B to investigate mixed-material erosion and redeposition properties of ITER relevant divertor materials. The beryllium containing plasma simulates the erosion of first wall material into the ITER sol plasma and its subsequent flow towards the carbon divertor plates. The experiments are designed to quantify the behaviour of plasma created mixed Be/C and Be/W surfaces. Developing an understanding of the mixed material surface behaviour is crucial to accurately predict the tritium accumulation rate within the ITER vacuum vessel. The temporal evolution of the plasma interactions with the various mixed surfaces are examined to better understand the fundamental mechanisms in play at the surface and to allow scaling of these results to the conditions expected in the ITER divertor. A new periodic heat pulse deposition system is also installed on PISCES-B to simulate the transient temperature excursions of surfaces expected to occur in the ITER divertor during edge localized modes (ELMs) and other off-normal events. These periodically applied heat pulses allow us to study the effects of transient power loading on the formation, stability and tritium content of mixed-material surfaces that are created during the experiments.
Highlights
A bilateral US(DOE)-EU(EFDA) collaboration, focused on experiments performed in the PISCES-B linear divertor simulator [1,2], utilizes a beryllium-seeded deuterium plasma to investigate mixed-material erosion and codeposition properties of ITER relevant divertor materials
The beryllium-containing plasma simulates the erosion of first wall material into the ITER sol plasma and its subsequent flow toward the carbon and tungsten material located in the ITER divertor region
The fundamental mechanisms responsible for the mitigation of chemical erosion from graphite surfaces exposed to beryllium containing deuterium plasma have been identified
Summary
A bilateral US(DOE)-EU(EFDA) collaboration, focused on experiments performed in the PISCES-B linear divertor simulator [1,2], utilizes a beryllium-seeded deuterium plasma to investigate mixed-material erosion and codeposition properties of ITER relevant divertor materials. Under identical plasma conditions, is increased on a different sample (to 1 x 1023 m-2), the same amount of beryllium is found in the surface, indicating that the subsequent beryllium deposited on the sample has been eroded These stationary Be depth profiles (with increasing fluence) are similar to earlier measurements made of carbon-tungsten mixed material surface layers [12] and indicate the formation of stable mixed-material surface layers. The optical windows in the PISCES-B vacuum system coat up due to the beryllium erosion of the incident beryllium plasma ion flux This interpretation of the Dgamma signal is corroborated by the analysis of witness plate samples located outside the plasma column during the discharge [5]. During a hightemperature target exposure (700°C), Figure 4b, the suppression of chemical erosion is much more rapid [6] and virtually no carbon is detected throughout the layer of collected material on the witness plate
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