**2. Overview**

This work helps to explain quantitative measurements of graphite ablation and oxidation rates in a hypersonic boundary layer using a new hot-surface plasma preheating technique to raise the temperature of the model to the required surface temperature for reentry studies in a hypersonic impulse facility [20]. Hot-wall reentry tests have been carried out in hypersonic impulse facilities [21] with temperatures characteristic of ablators in hypervelocity reentry of approximately 2000–3000 K in 8.6 km/s for Earth reentry flow [22]. Experiments with electrically preheated graphite samples using uniform width profiles were conducted at the University of Queensland's X2 expansion tunnel [23] for surface temperatures from 1770 to 2410 K used to target the carbon–nitrogen violet band [24]. All of these used resistive heating on a uniform width profile and not a plasma preheating technique. Recent experiments based on Orion reentry conditions used a surface temperature of about 2800 K [25] and Apollo 4 lunar return speed of 11 km/s reportedly experienced a surface temperature of about 2400 K [26], while typical reentry surface temperatures for Space Shuttles was about 1740 K [25]. This present work has achieved temperatures in excess of 2500 K on a preheated graphite surface used for the assessment of mass loss through ablation in a Mach 4.5 and Mach 6 flows. The use of a plasma as the means of heating the disc was proven to be effective for reaching temperatures of these magnitudes [27] and the process has potential to be more widely used for similar experiments [28]. The technique uses a plasma heating source with argon flow [29]. The work reports the first-time quantification of ablation and oxidation rates of a heated carbon disc up to 500 milliseconds duration in 500 Pa vacuum pressure in a hypersonic wind tunnel facility using a plasma preheating methodology.
