Persistent Sputtering Yield Reduction in Plasma-Infused Materials for Plasma Propulsion and Fusion

Material sputtering provides challenges for plasma devices from space propulsion to fusion. In this talk, Prof. Wirz will discuss plasma-material interactions for plasma thrusters and recent developments towards fusion plasma materials. Plasma thrusters are predominantly driven by thruster component lifetime through erosion and ion and electron induced “facility effects” during ground testing that obfuscate the thruster’s anticipated on-orbit performance. Recent developments in these areas have revealed material approaches that may help fusion devices, which must address both component lifetime and plasma performance via reduction of contaminants.

In particular, we have shown that metallic foams provide geometric trapping and interface/sheath manipulation that can exhibit persistent sputtering yield reductions of 40% to over 80% compared to a flat surface under 100 to 300 eV argon plasma bombardment. These results show a strong yield dependence based on the relationship between foam geometry and plasma sheath size. For foam pore sizes near or larger than the sheath thickness, the plasma infuses the foam and transitions the plasma-surface interactions from superficial to volumetric phenomena. By defining a plasma infusion parameter, the sputtering behavior can be separated into the plasma-facing and plasma-infused regimes. While plasma infusion leads to a larger effective sputtering area, geometric recapture of ejected particles facilitates an overall reduction in yield. For a given level of plasma infusion, the reductions in normalized yield are more pronounced at lower ion energies since angular sputtering effects enable more effective geometric recapture of sputterants. Opportunities for plasma-infused materials in space propulsion and fusion will be discussed.