Dusty plasma experiments relating to noctilucent clouds

Summary form only given, as follows. Noctilucent clouds (NLC), polar mesospheric summer echoes (PMSE) and localized "bite-outs" in the density of free electrons are caused by small ice particles in the lower ionosphere. Rocket-borne charge collectors have recently found evidence for both positive and negative aerosols near NLC and PMSE layers (Havnes et al., JGR 101, 10839, 1996). The mass distribution of these particles and the reaction rates for electron attachment, photoionization, photodetachment, etc. which are necessary for modeling are not known. Two new experiments are underway to answer these questions. First, a rocket-borne charge-collecting probe with a magnetic field for mass discrimination has been constructed and tested in the laboratory. The magnetic field prevents collection of singly-charged species with mass below a threshold determined by the rocket velocity and the magnetic field strength. Laboratory tests of a prototype probe show that the magnetic field is effective in preventing collection of low energy electrons. Second, a large plasma chamber (0.9 m diameter/spl times/1.2 m) is being fitted with a supersonic nozzle which generates ice clusters. Clusters which become charged will be detected by Faraday cups and their mass distribution will be determined by mass spectrographs. Electron attachment rates will be inferred from the dependence of the charged fraction on the electron density. An arc lamp source with a cutoff wavelength similar to that of the solar spectrum at 80 km will be used to determine the role of photodetachment and possibly photoionization. Sodium or other impurities may be added to the flow creating the particles to determine whether or not their presence results in a lower work function.