Beryllium flux distribution and layer deposition in the ITER divertor

Abstract

Abstract.The deposition of Be eroded from the main chamber wall on the W surfaces in the ITER divertor could result in the formation of Be rich Be/W mixed layers with a low melting temperature compared to pure W. To predict whether or not these layers form the Be flux distribution in the ITER divertor is required. This paper presents the results of a combination of plasma transport-with erosion/deposition simulations that allow to calculate both the Be flux distribution and the Be layer deposition in the ITER divertor. This model includes the Be source due to Be erosion in the main chamber and the deposition, re-erosion and re-deposition of Be in the ITER divertor. The calculations show that the fraction of Be in the incident particle flux in the divertor range from ≈ 10 −3 to ≈ 5% with a pronounced inner outer divertor asymmetry. The flux fractions in the inner divertor are on average ten times higher than in the outer divertor. Thick Be layers only from at the inner strike point and the dome baffles. The highest Be layer growth rate is found to be 1.0 nm/s. Despite the Be deposition the formation of Be rich Be/W mixed layers is not to be expected in ITER. The expected surface temperature at these locations during steady state operation is too low as to result in Be diffusion into W and thus Be/W mixed layers can not form.

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

“…To evaluate equation (2), the fluxes of Be ions and atoms in the divertor were taken from [2]. In that work, calculations of Be erosion at the main wall were combined with plasma transport and erosion/deposition simulations to account for re-erosion and re-deposition of Be in the full W divertor of ITER.…”

“…In that work, calculations of Be erosion at the main wall were combined with plasma transport and erosion/deposition simulations to account for re-erosion and re-deposition of Be in the full W divertor of ITER. Figure 1 shows the poloidal profile of the ITER divertor and its discretization as used in the Be flux distribution calculations [2], which was also adopted in the present work for the calculations of the gap trapping probability η. The deuterium (D) plasma background with argon (Ar) as the main radiating impurity from B2/EIRENE calculations [4] was used.…”

“…Except for Ar seeding, this plasma background corresponds to a high power ITER reference discharge with 130 MW power going into the SOL. The poloidal profiles of the D + ion flux, mean impact energy, and the Be flux fractions used in the present work are shown in figures 7 and 11 in [2]. For the integration of equation (2) the profiles of Be flux fractions were interpolated between given data points independently for all charge states.…”

“…The poloidal profile of the total Be influx into the gaps based on the data from [2] is shown in figure 2. As a result of a set of 3D-GAPS simulations performed for poloidal gaps in various regions of the divertor with the corresponding variation of plasma parameters and charge-resolved Be fluxes impacting on PFCs, the poloidal dependence of parameter η in equation (2), i.e.…”

“…In ITER, co-deposition of T will happen substantially with beryllium (Be) eroded from the first wall, therefore modelling concerning Be transport and re-deposition in ITER, especially inside gaps of castellated PFCs, is essential to study the possible influence on the ITER duty cycle. Modelling of Be transport and redeposition at plasma-wetted areas in the divertor of ITER has been performed earlier [2][3][4]. This paper presents an estimation of the contribution of gaps in a full tungsten (W) divertor of ITER to beryllium deposition and resulting tritium retention by co-deposition.…”