Effects Of Collisional Processes Research Articles

Auroral N2 emissions and the effect of collisional processes on N2 triplet state vibrational populations

Previous model results have shown that the N2 triplet vibrational level populations in the aurora are strongly affected by cascade and quenching by atomic and molecular oxygen. As the aurora penetrates to lower altitudes (less than 100 km) the role of quenching by atomic oxygen becomes less important and processes involving N2 collisions begin to play a more prominent part. We are developing a model which will yield steady state vibrational level populations for both the singlet and triplet valence states of N2. The model currently provides results for the seven low‐lying N2 triplet states (A 3Σu+, B 3IIg, W3Δu, B′ 3Σu−, C3IIu, D3Σu+, and E3Σg+). These states are responsible for auroral emissions from the UV (Vegard‐Kaplan (VK), second positive (2PG)) through the visible to the infrared (first positive (1PG), infrared afterglow (IRA), Wu‐Benesch (WB)). We have included two additional collisional processes in the current model which were not treated previously. These are the intersystem collisional transfer of excitation (ICT) between the B state and the A, W, and B′ states and vibrational redistribution within the A state vibrational manifold, both due to collisions with ground state N2. The present work compares our current model results with those of a previous model, as well as ground, airborne, and rocket observations. The comparison between N2(A) (VK) and N2(B) (1PG) vibrational level populations predicted by our model and a number of auroral observations indicate that the current model achieves a significant improvement in the fit between calculation and observation. In addition, the current model predicts a shift in the band intensity distribution of the 1PG Δν = 3 sequence from the infrared into the visible red at the lower altitudes (less than 90 km) as well as an overall enhancement in the entire 1PG system. Consequently, this provides a possible explanation of a dominate feature of type b aurora, the auroral red lower border.

Effects of collisions on the nonlinear particle dynamics in the magnetotail

The effects of collisional processes on the nonlinear particle dynamics in the magnetotail are considered. A simple collision operator is developed to model the effects of pitch‐angle and energy scattering. It is found that the phase space partition persists for up to moderate scattering amplitudes in pitch‐angle and energy, and that certain distribution function features are robust even in the presence of large amplitude collisions. It is shown that if the collisions are due to short scale length electrostatic fields, excessively large field amplitudes are required to significantly alter the phase space structures and the resulting distribution function features.

Cw and improved pulsed operation of the 14- and 16-μm CO2 lasers

The performance of the 14- and 16-μm CO2 lasers produced in the electric discharge gasdynamic laser has been significantly improved by the addition of a small percentage of H2 to deactivate the (0110) level. This addition tripled the pulsed output of the laser, and 45 μJ at 14 μm and 25 μJ at 16 μm were observed. cw oscillation was achieved for the first time, with output powers of 0.6 and 0.9 W, respectively. The effect of collisional processes in limiting the CO2 density is discussed.