Advances in inductively-coupled-plasma heaters for aerothermal testing of thermal-protection systems

Inductively coupled plasma (ICP) heaters generate high-enthalpy and ultra-clean plasma flows through electromagnetic coupling discharge, and are of significant value in the research on thermal protection materials (TPMs) for hypersonic vehicles. This paper systematically reviews the research progress of ICP heaters in four core aspects: theoretical modelling and numerical simulation, facility development, parameter diagnostics and engineering applications. The theoretical analysis has evolved from simplified one-dimensional models to self-consistent multi-dimensional models, and numerical simulations have progressed in tandem, playing key roles in investigating transport processes and non-equilibrium characteristics within the heaters. Worldwide, a series of ICP facilities with power ranging from tens of kilowatts to the megawatt levels have been developed. Based on contact measurements and optical diagnostics, the macro-parameters (e.g., heat flux, electron number density) and micro-characteristics (e.g., electron temperature, translational temperature, species concentration) have been revealed for regions both inside the heater and in its plasma jet. ICP heaters are capable of stably providing a thermal environment with enthalpy up to nearly 100 MJ/kg at sub-atmospheric pressures for long-duration testing, and are widely used for studying surface catalysis, ablation behavior, and gas-solid coupling reaction mechanisms of various TPMs, thus providing a scientific basis and experimental support for the design and performance evaluation of advanced TPMs.