Surface morphology and helium retention on tungsten exposed to low energy and high flux helium plasma

“…[46]. In contrast to this observation no blistering was observed in a similar experiment, but at lower sample temperatures ( 900 K instead of 1850-2850 K) [47]. Whether this different behaviour is due to the different temperatures leading to different He diffusivities and to a different vacancy concentration and mobility, or whether this is due to different W material grades has not been resolved yet.…”

Section: Displacement Damages Hydrogen Retention and He-bubble Formacontrasting

confidence: 57%

High-Z plasma facing components in fusion devices: boundary conditions and operational experiences

Neu

2006

Phys. Scr.

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In present day fusion devices optimization of the performance and experimental freedom motivates the use of low-Z plasma facing materials. However in a future fusion reactor, for economic reasons a sufficient lifetime of the first wall components is essential. Additionally, tritium retention has to be small to meet safety requirements. Tungsten appears to be the most realistic material choice for reactor plasma facing components (PFCs) because it exhibits the lowest erosion. But besides this there are a lot of criteria which has to be fulfilled simultaineously in a reactor. Results from present day devices and from laboratory experiments confirm the advantages of high-Z PFM but also point to operational restrictions, when using them as PFCs. They are associated with the central impurity concentration, which is determined by the sputtering yield, the penetration of the impurities and their transport within the confined plasma. The restrictions could exclude successful operation of a reactor, but concomitantly there exist remedies to ameliorate their impact. Obviously some price has to be paid in terms of reduced performance but lacking of materials or concepts which could substitute high-Z PFCs, emphasis has to be put on the development and optimization of reactor relevant scenarios which incorporate the experiences and measures.

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“…The bias voltage of -80 V was applied to the W sample resulting to the incident energy of Deuterium and helium retention in the W samples was monitored ex-situ using thermal desorption spectrometry (TDS). An infrared heater was used to heat the samples at a ramp rate of 0.5 K/s and the sample temperature was raised to 1300 K. HD, 4 He and D 2 molecules released during TDS run were monitored by the HRQMS. To calculate the relative contribution of the recorded HD and D 2 masses to the total release of deuterium, the partial currents of the HRQMS were normalized as described in Ref.…”

Section: Methodsmentioning

confidence: 99%

“…It is known that He irradiation leads to such structure modification as bubble formation, vacancy swelling, blistering, flaking, porous surface structure, depending on the irradiation conditions [1][2][3][4][5][6][7]. Retention of hydrogen isotopes in W is enhanced by pre-irradiation with He ions at energies of several keV [8][9][10][11][12], whereas sequential 500 eV He 473K significantly reduces the number of blisters [15].…”

Section: Introductionmentioning

confidence: 99%