Parametric studies of carbon erosion mitigation dynamics in beryllium seeded deuterium plasmas

The characteristic time of protective beryllium layer formation on a graphite target, τBe/C, has been investigated as a function of surface temperature, Ts, ion energy, Ei, ion flux, Γi, and beryllium ion concentration, cBe, in beryllium seeded deuterium plasma. τBe/C is found to be strongly decreased with increasing Ts in the range of 550–970 K. This is thought to be associated with the more efficient formation of beryllium carbide (Be2C). By scanning the parameters, a scaling expression for τBe/C has been derived as τ Be / C [ s ] = 1.0 × 10 - 7 c Be - 1.9 ± 0.1 E i 0.9 ± 0.3 Γ i - 0.6 ± 0.3 exp ( ( 4.8 ± 0.5 ) × 10 3 / T s ) , where cBe is dimensionless, Ei in eV, Γi in 1022 m−2 s−1 and Ts in K. Should this scaling extend to an ITER scenario, carbon erosion of the divertor strike point region may be reduced with characteristic time of ∼6 ms. This is much shorter than the time between predicted ITER type I ELMs (∼1 s), and suggests that protective beryllium layers can be formed in between ELMs, and mitigate carbon erosion.