Carbon removal from tile gap structures with oxygen glow discharges

Abstract

The removal of redeposited layers from tile gap structures with ITER-like geometries was investigated with various lowtemperature glow discharges in oxygen. The test structure consists of 19 mm deep gaps with widths ranging from 0.5 to 4 mm. Erosion rates inside the gaps are reduced compared with a directly exposed witness surface. Smallest erosion is found for the lowest particle energies. Erosion at the bottom of the gap increases linearly with the gap width. Erosion on the side walls drops nearly exponentially with increasing distance from the top. Side wall erosion dominates the total eroded amount for all cases investigated. The total eroded amount integrated over the whole inner gap surface is larger than the amount that would be eroded on a flat surface with an area identical to the gap opening.

Fuel removal from tile gaps with oxygen discharges: reactivity of neutrals

“…For easier comparison with the following figure the displayed profiles are normalized to the maximum erosion observed at the side walls of the widest gap. Erosion is maximal at the entrance and decreases rapidly with increasing distance from the top in accordance with results we obtained earlier [27]. Other than in the previous experiment [27] the Si samples for the tile gap side walls were laser cut so that the edges were not only flush with the top but also with the bottom surface of the copper cuboids.…”

“…A basic description of PLAQ is given in [20] and the present configuration is described in [27]. In short, PLAQ consists of a stainless steel chamber and is equipped with an electron-cyclotron-resonance (ECR) plasma source operating at 2.45 GHz.…”

“…The distance between the bottom of the cage and the substrate holder is 100 mm. For all the experiments presented in this article, the bottom of the plasma cage is closed with a solid plate so that the line of sight between the plasma and the substrate holder is blocked (see figure 1 in [27]). Particles can only leave the plasma through the side wall of the cage made of a metal mesh.…”

“…Besides exposure of a flat sample, different 3D structures are exposed to the O 2 discharge in the remote position. One is the so-called tile gap test structure (TGTS) already described in [27] where also a photograph is shown. The other one is a so-called cavity.…”

“…In a recent study we exposed deep gaps with variable aspect ratio to different oxygen discharges at room temperature [27]. We found that removal of carbon layers inside the gaps is possible even if there is no direct plasma contact.…”