Nautilus: A tool for modeling fluid plasmas

Plasmas are important in many situations including space and solar physics, lightning, re-entry heating and nuclear fusion. It's most often the case that the plasma is generated from a cold neutral fluid so there is a transition regime where the plasma is neither fully ionized nor neutral. Furthermore in most high temperature devices a significant amount of neutral fluid may exist (particularly near the wall). As such, is is important that even for high temperature plasmas the transition regime between fully ionized and non-ionized plasmas be modeled. In addition, given the wide variety of temperature and densities that can exist in plasmas, there are many, many different plasma models that are relevant in the different situation. Nautilus is a code that is a collection of these various plasma fluid models encompassing the regimes of neutral flow (important in aeronautics) to high temperature plasmas important in nuclear fusion. The fluid models can use either ideal gas laws or general equation of state. Radiation transport can also be modeled. This paper outlines the physics modeled in Nautilus along with the algorithms and various applications including plasma jet merging, FRC formation and collisionless reconnection.