Observations of visible light emission from interactions between an electrothermal plasma and a propellant

A set of experiments has been conducted on the experimental plasma-propellant interaction facility PIPE to measure the burn rates of JA2 solid propellant as a function of plasma impingement angle with respect to the propellant surface. The propellant test stand is designed such that the angle of plasma impact on the propellant surface can be varied 0 to 90 degrees. Optical emission spectroscopy measurements were taken during these shots. Fiber optics were situated in two places, one closer to the plasma source and the second at the propellant´s rear edge near the point of impact of plasma and propellant. The fiber optics are connected to an optical multichannel analyzer set to observe neutral copper lines and molecular C₂ Swan Bands in the 505-585 nm spectral region. Time-averaged core are temperatures of 8,800 to 14,000 K and plasma densities of 2×10²⁵ to 4.5×10²³ m^-3 have been deduced by measurements along the axis of the device using the relative intensities and the Stark broadening of the copper lines. As the angle of plasma impact with the propellant surface increases from D to 90°, the overall radiant emission increases, falls and increases. However, the measured plasma temperature decreases gradually and plasma density falls by nearly a factor of two before increasing substantially at 90°. Comparisons with the measured burn rates of the JA2 propellant versus inclination angles suggests a stronger correlation of plasma burn rate with plasma kinetic energy than with the radiative heat flux