Chemical sputtering yields of carbon based materials at high ion flux densities

Abstract

Graphite and advanced carbon fiber composites (CFC) are widely used inside the vacuum vessel of magnetic fusion devices. However, erosion by chemical sputtering via hydrocarbon formation might limit their application as target material in future machines like ITER. The first systematic study of the chemical erosion of graphite and different CFCs (including a silicon-doped one) as a function of ion flux density in the range of 1.4 × 10 21 -5 × 10 22 m -2 s -1 was performed in the plasma generator PSI-1. The results of three different analysis methods agree within about 40%.No differences in the chemical erosion yields between hydrogen and deuterium exposures are found for the various materials. In contrast, the erosion yields differ up to a factor of two for the different CFC-materials. In general, the chemical sputtering yields decrease with increasing ion flux density according to -0.6 reaching levels below 1% at the highest fluxes. Scanning electron microscopy (SEM) and energy dispersive Xray analysis (EDX) show preferred erosion in the area between the carbon fibers.

Low-energy tritium ion erosion of graphite

“…The general trends of yield vs. energy and yield vs. temperature were similar for bombardment by both H + and D + -with D + -induced chemical erosion yields being up to two times higher under some energy-temperature conditions: e.g., 300 K graphite at <25 eV, or 600-800 K graphite at >50 eV [6]. Chemical sputtering by high plasma flux densities also revealed no significant isotope effect [13]. In contrast, mass-loss measurements suggest that the erosion yield at 300 K due to D + is up to five times greater than that of H + , for energies <50 eV [8].…”

Plasma-material interactions in current tokamaks and their implications for next step fusion reactors

“…The models developed for energetic ion impact on carbon [293,294] are extensions of the thermal atom impact model of Horn et al [287]. Experimental erosion yields for D ions from weight loss and mass spectroscopy are [295,296] and in the tokamak edge plasma [297][298][299].…”

“…Physical sputtering is also shown (dotted line.) [288,289,302,303], spectroscopic measurements from plasma simulators [295,296,304,305] and from the ASDEX-Upgrade divertor [298]. The curves are fits to the data using the models described in [285,293].…”

Bayesian inference in surface physics

“…Filled circles correspond to the subset for which the fitting curve (solid line) is valid (E0 = 30eV,T=600K).Open triangles and squares represent data from Ref. [45] and [46], respectively, while the full symbols show the data sets after multiplication with the corresponding scale factor (0.72 and 0.32). Error bars show the assigned experimental error.…”

“…The mean of the threshold value is θ 0 = 28.8 · 10 −23 m 2 s with scale factors of γ = 0.72 and γ = 0.32 for the data from Ref. [45] and [46], respectively.…”