Influence of Ablation on Vacuum-Ultraviolet Radiation in a Plasma Wind Tunnel Flow

Plasma wind tunnel experiments have been performed simulating a Hayabusa reentry trajectory point at 78.8km altitude with a velocity of 11.7km/s corresponding to a local mass-specific enthalpy of 68.4MJ/kg and a stagnation pressure of 2.44kPa. Ablation-radiation coupling is investigated using a carbon preform sample, a lightweight carbon phenolic ablator sample, and cooled copper. Optical emission spectroscopic measurements in the vacuum ultraviolet (VUV) regime (116-197nm) have been conducted through a bore hole in the stagnation point of the different samples. Optical emission spectroscopic measurements in the UV/VIS spectral range (320-810nm) have been conducted viewing the plasma from the side. The stagnation point VUV radiation to the carbon preform sample is strongest, whereas it is weakest for the carbon phenolic sample. In the UV/VIS both carbon-based material samples lead to stronger plasma radiation than copper. Atomic number densities in front of the samples are largest for the carbon preform sample and lowest for the carbon phenolic sample. Rotational and vibrational temperatures are lower for both the carbon-based materials compared with copper. The measurements show for the first time experimentally the radiative heat flux mitigation by carbon phenolic materials.