Differential Sputtering Behavior of Pyrolytic Graphite and Carbon-Carbon Composite Under Xenon Bombardment

Abstract

A differential sputter yield measurement technique is described, which consists of a quartz crystal monitor that is swept at constant radial distance from a small target region where a high current density xenon ion beam is aimed. This apparatus has been used to characterize the sputtering behavior of various forms of carbon including polycrystalline graphite, pyrolytic graphite, and PVD-infiltrated and pyrolized carboncarbon composites. Sputter yield data are presented for pyrolytic graphite and carbon-carbon composite over a range of xenon ion energies from 200 eV to 1 keV and angles of incidence from Oo (normal incidence) to 60°.

Sputtering Yield of Carbon-Carbon Composite Due to Xenon Ion Bombardment in Ion Engines

“…However, it is reported that the average sputtering yield remains nearly constant 13) because the carbon fibers are distributed randomly in the horizontal and vertical directions. Thus, incorporating the time-independent common structure of the C/C surface in the sputtering yield model will be sufficient for engineering applications.…”

“…[3][4][5] Four sputtering yield models were used: 1) CSU model, 2) MD model, 3) YK model, and 4) C/C model (w ¼ 0:8). The CSU model was based on the measurements 13) by Williams et al at Colorado State University (CSU), and the MD model used a database setup by Muramoto's MD simulations. Because the range of incidence energy is limited between 200-1,000 eV in the CSU experiments and 100-500 eV in the MD simulations, values outside of these energy ranges were extrapolated by linear fitting.…”

“…Large amounts of experimental data are available for the normal incidences of graphite, diamond, and pyrographite, [8][9][10][11][12][13][14][15] that can be used to derive some empirical formula by curve-fitting, and this approach is widely used in engineering applications. In contrast, only small amounts of experimental data are available to derive an empirical formula for the angular dependence of sputtering.…”

“…[12][13][14] The working fraction w was assumed to be 0.8 for a density of 1.6 g/cm 3 . The sensitivity of the C/C model to the working fraction was studied changing the working fraction to 0.5 and 1.0.…”

JIEDI Tool: Numerical Life Qualification Tool for Ion Engine Optics

“…The sputtering yield of the grid material is incorporated using experimental data 5) in the form of tables of values for incident energies and incident angles. Studies are now underway to develop C/C sputtering models in the JIEDI project.…”