Interior Spectroscopic Investigation of the Propellant Energy Modes in an Arcjet Nozzle
Abstract : Internal emission spectroscopy measurements were performed in the nozzle expansion region of a 26 kW class ammonia arcjet. A series of three optical access ports (0.020-inch diameter) were equally spaced along the center line of the expansion nozzle. Atomic and ionic excitation temperatures of H and NII were determined through the use of Boltzmann plots. Electron density measurements were also taken based upon Stark broadening of the hydrogen beta Balmer transition. It is believed that a change in the mechanism governing the electron density occurred just downstream of the constrictor between the first two access ports lending evidence that arc attachment is occurring in this region. Although the trends for excitation temperatures and electron density were similar to those previously observed in 1 kW arcjets, the temperature values were found to be significantly less. In addition, vibrational and rotational temperatures of NH were measured and appeared to be frozen throughout the expansion nozzle.
Exit-plane electrostatic probe measurements of a low-power arcjet
Improved understanding of the flow processes in a 1-kW hydrazine constricted arcjet is achieved with multiple electrostatic probe surveys in the exit-plane region of the plume. Quadruple, triple, and single electrostatic probe techniques are utilized for measurements of the electron temperature Te9 density ne, and ratio of ion axial velocity to most probable thermal speed n,/cm,H+. Centerline axial profiles of Te and nc are presented for 2.2-6.2 mm downstream of the exit-plane, yielding Te = 6600 K ± 15% and nc 3.6 x 10 12 cm"3 ±60% close to the thruster exit. Quadruple probe theory is modified to account for radial gradients in Te and ne over the probe radial dimension, and is used to extract exit-plane radial Te and ne profiles. Floating probe measurements yield estimates of the radial electric-field profile at the thruster exit, implying a small amount of current and ohmic heating downstream of the exit-plane. Ak cm E e / I lb 7, j k L m n
Ionization by drift and ambipolar electric fields in electronegative capacitive radio frequency plasmas.
Unlike α- and γ-mode operation, electrons accelerated by strong drift and ambipolar electric fields in the plasma bulk and at the sheath edges are found to dominate the ionization in strongly electronegative discharges. These fields are caused by a low bulk conductivity and local maxima of the electron density at the sheath edges, respectively. This drift-ambipolar mode is investigated by kinetic particle simulations, experimental phase-resolved optical emission spectroscopy, and an analytical model in CF(4). Mode transitions induced by voltage and pressure variations are studied.