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.
Arcjet anode plasma measurements using electrostatic probes
A 1-kW hydrazine arcjet thruster has been modie ed for internal probing of the anode sheath boundary layer with an array of 14 electrostatic microprobes e ush mounted into the anode body. Axial and azimuthal distributions of the plasma properties e oating potential, anode sheath potential, wall current density, electron number density, and electron temperature have been obtained for arc currents between 7.8 and 10.6 A and propellant e ow rates of 40 ‐60 mg/s. The specie c power ranged from 18.8 to 27.4 MJ/ kg. Azimuthal symmetry has been verie ed for all arcjet operating conditions. The electron temperature data show that the near-anode plasma is highly nonequilibrium. Most of the current density and anode heating is located within 2 ‐4 mm of the constrictor exit, with the location affected more by mass e ow rate than by arc current. The axial anode heating distribution is closely coupled to current density and accounts for ;18‐24% of the total input power. Reasonable agreement between a numerical model and experimental results is found for a constant value of the electron inelastic energy-loss factor.
The electronic structure of the first row hydrides BH, CH, NH, OH and FH II. Excited states
Previous calculations on the ground states of the hydrides are extended to include the stable excited states. The ab initio orbital calculations predict vertical excitation energies which differ from the experimental values by as much as 2eV. However, when allowance is made for the effects of atomic electron correlation all errors in the calculated excitation energies become less than 0·2eV. The locations of excited states of different multiplicities from those of the ground states are predicted to within this accuracy. The oscillator strengths of allowed transitions from the ground states are calculated using both the dipole-length and dipole-velocity formulae. The dipole-length values are in fair agreement with the only experimental value available (for OH2ll → 2∑+), whereas the dipole-velocity values are much too large. Possible improvements in the accuracy of the calculations are discussed.