Study of carbon erosion under ion bombardment at high temperature: Application to the thermal protection system of Solar Probe+

Abstract

Solar Probe+ (SP+) will employ a combination of in situ measurements and imaging to achieve the mission’s primary scientific goal: to understand how the Sun’s corona is heated and how the solar wind is accelerated. The Solar Probe+ thermal protection system (TPS) can be a carbon–carbon (C–C) composite shield, reaching temperatures of 1600–2100 K and submitted to radiation effects including physical sputtering, chemical erosion, sublimation and radiation-enhanced sublimation (RES). In this study, different numerical codes were used to describe the behaviour of a carbon-based thermal protection system. The physical sputtering yield of carbon by hydrogen and helium ions is less than 2%. The maximum implantation yield of ions is more than 85% and the implantation depth is around 100 nm for hydrogen and 150 nm for helium. This could have a great influence on the material properties and its chemical erosion, characterized by the production of hydrocarbons (acetylene and methane) and consequently the degradation of the composite and the pollution of the measurement of the onboard instruments. Finally, an experimental study is also done on polycrystalline graphite to observe the various erosion mechanisms of the material under extreme conditions.