Self-consistent Interaction of Neutrals and Plasma at Shock Waves

The heliosphere creates a bow shock as it moves through the local interstellar medium (LISM), assuming it does so supersonically. Since the LISM is partially ionized and neutral hydrogen is coupled to the plasma through charge exchange, the bow shock might be modified in structure by this interaction. To explore the interaction of neutral gas and a collisionless plasma shock, we have developed a semi-analytical model which describes plasma-neutral gas-interaction in a self-consistent manner, combining the gas-dynamical equations of a plasma with the Boltzmann equation describing the neutral gas. Solving the interaction analytically is rather complicated since the plasma drift velocity and plasma velocity distribution function (VDF) enter into the Boltzmann equation of the neutral gas. To solve the system, the neutral VDF is expanded first in terms of Legendre polynomials and then in Laguerre harmonics. Retaining only the first few harmonics, which contribute the most, we are able to study the shock structure semi-analytically, thereby revealing a more basic understanding of shock processes in a partially ionized medium and illustrating the mediation of the plasma shock by neutral hydrogen.