Q2. What is the effect of ion-induced trapping on the inventory?
After saturating available traps in the ion induced damage profile, inward diffusion and subsequent trapping at bulk lattice defects increases the trapped inventory.
Q3. What is the way to assess the effect of ELMs on divertor materials?
In order to assess the effect of ELMs and disruptions on divertor materials, plasmaguns [28,29,30] are used to provide realistic conditions [2] (i.e., adequate pulse duration and energy density), as transient heat loads expected in ITER are difficult to achieve in existing tokamaks.
Q4. How long does the divertor life last?
Forcarbon in the divertor, redeposition of eroded material reduces the net-erosion resulting in component lifetime of about 10 000 discharges, i.e. longer than the foreseen exchange periods of the divertor cassettes [85].
Q5. What is the first step in the chain of processes determining the lifetime of a plasma facing?
The first step in the chain of processes determining the PFCs lifetime, leading to dustgeneration and tritium retention by co-deposition, is the erosion of the wall material.
Q6. What are the main parameters of the dust generation in tokamaks?
In tokamaks, dust can be produced during various operation phases:• Layer deposition and disintegration in steady state• Disruptions • Arcing [47,48]•
Q7. How much energy density should be used for CFC and W?
In conclusion, for both CFC and W, ELMs in ITER should be limited to an energy density of 0.5 MJ/m2 to avoid serious damage and limitations of PFCs lifetime, as has been recognised by the ITER team.
Q8. What is the sputtering yield of a plasma facing material?
The chemical sputtering yield exhibits a maximum at elevated surface temperatures (around 10-1 at 600-800 K), a decrease at high incident fluxes (below 10-2 [19] above 1022 D/m2s), and a decrease towards a threshold energy (see fig.
Q9. What is the effect of the ion-induced trap generation on the inventory?
In these calculations no ion-induced trap generation has been taken into account due to the very shallow implantation depths leading to a retention increase with the square-root of fluence.
Q10. What is the model of the tritium inventory in W?
Figure 5 shows modelling of the tritium inventory in W under ITER conditions [69,70] and predicts that it stays in tolerable limits for polycrystalline W in ITER neglecting n-irradiation damage.
Q11. How many discharges will be required to reach the T limit?
in the all-C option, the T limit will be reached in a few tens of discharges and require frequent cleaning intervention.
Q12. What is the main concern for next step devices?
Although the issue could be attenuated in a divertor configuration with more efficient impurity screening, this new operational limit could be a serious concern for next step devices running repetitive discharges over long duration, leading to significant deposited layers thicknesses.
Q13. How much is the erosion rate in the ITER divertor?
As an example, recent modelling of the ITER divertor with the ERO code for carbon transport yields a local re-deposition fraction as high as 99 % [25] with a net erosion rate 100 times lower than the gross erosion rate.•
Q14. What are the main uncertainties in the dust generation process?
Dust generation mechanisms, conversion of deposited layers to dust, dust transport and mobilisation need to be studied in greater detail.
Q15. What is the saturation value of n-produced trap in W?
The saturation concentration of n-produced trap of 1% in W is an extreme upper limit and probably 0.1% is a more realistic value for ITER.