Laboratory simulations of the solar wind-comet interactions

The laboratory simulation of the solar wind interaction with a comet is carried out to study the cometary neutral gas ionization and the influence of the ionization process on bow shock formation. The UCR T-1 facility is used for the simulations, an ice ball as a comet model and photographs and data are taken under a variety of solar wind velocity, interplanetary magnetic field and comet configurations. The results show that the cometary neutral gas ionization depends on both the velocity of the solar wind and the interplanetary magnetic field. The plasma cloud surrounding the comet is visible only when the solar wind velocity and IMF are both above minimum values. This velocity dependent phenomena is explained by Alfven's critical ionization velocity effect. This critical magnetic field effect may be caused by the lower hybrid instability triggering ionization of the neutral gas by plasma flow. The magnetic component of electromagnetic instabilities are investigated both with and without the CIV effect. Four groups of waves are found and identified to lie in the range of lower hybrid waves. The cometary bow shock formation is studied with the neutral gas ionization conditions satisfied. A contact discontinuity and a collisional bow shock are found