Laboratory simulation of plasma phenomena in comets

A model experiment simulating the interaction between the solar wind and comets is described. The aim is to study the ionization and acceleration of molecules in the atmosphere of a comet. A plasma stream (ne = 1013 cm−3, Te = 3 ev, υ = 6 × 106 cm/sec) in a vacuum tunnel interacts with a cloud of CO2 gas sublimated from a dry ice core of 1-cm radius. The gas density at the surface of the ice is 5 × 1013 cm−3. Diagnostic methods include image converter photography and spectrography. The interaction, which is characterized as collisionless, gives rise to a well-defined tail developing to a length of 20 cm within 10 μsec after the first impact of the stream against the cloud. A visible coma extends about 3 cm in front of the ice. The CO2 gas is found to be substantially ionized and dragged along with the stream. The ionization is believed to be explainable in terms of an increased average electron energy caused by the interaction. The drag on the ions is probaly due to magnetic coupling to the plasma stream.