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-pro pellant interaction facility PIPE to measure the burn rates of JA2 sol id propellant as it 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 varie d 0 to 90 degrees. Optical emission spectroscopy measurements were tak en during these shots. Fiber optics were situated in two places, one c loser to the plasma source and the second at the propellant's rear edg e near the point of impact of plasma and propellant. The fiber optics are connected to an optical multichannel analyzer set to observe neutr al copper lines and molecular C-2 Swan Bands in the 505-585 nm spectra l region. Time-averaged core arc temperatures of 8,800 to 14,000 K and plasma densities of 2 x 10(23) to 4.5 x 10(23) m(3) have been deduced by measurements along the axis of the device using the relative inten sities and the Stark broadening of the copper lines. As the angle of p lasma impact with the propellant surface increases from 0 to 90 degree s, the overall radiant emission increases, falls and increases. Howeve r, the measured plasma temperature decreases gradually and plasma dens ity falls by nearly a factor of two before increasing substantially at 90 degrees. Comparisons with the measured burn rates of the JA2 prope llent versus inclination angle suggests a stronger correlation of plas ma burn rate with plasma kinetic energy than with the radiative heat f lux.