Modeling of plasma propulsion using an inflated magnetic field and its interaction with a fast plasma stream.

摘要

It has been proposed to extract momentum from the solar wind for spacecraft propulsion in deep space. For this purpose, a magnetic bubble is inflated from the spacecraft. The magnetic bubble inflation is affected by the expansion of a dense warm plasma in the magnetic field created by a solenoid aboard the spacecraft. The interaction between the inflated magnetic field and solar wind is likely to affect the transfer of momentum for the purpose of propulsion. The aim of our research here is to study the feasibility of this propulsion scheme by means of numerical simulations. For this purpose, we developed a 3-D hybrid particle code to model (i) the expansion of plasma in an ambient magnetic field created by a solenoid and (ii) the interaction of a plasma stream with the inflated magnetic field. The code is hybrid in the sense that ions are treated as particles and electrons as an isothermal fluid. We solve the coupled set of Maxwell's equations and the electron momentum equation for the electromagnetic fields using a predictor-corrector method.; Using the 3-D simulations, we have demonstrated that when a warm and high-density plasma is injected in solenoidal magnetic fields, the trapping of the plasma in a magnetic mirror creates a dense plasma. When the trapped plasma energy densities (thermal and dynamic) exceed the magnetic energy density, the expanding plasma inflates the magnetic field lines. The extent of field inflation is seen to be greatly dependent on the injection velocity of the thermal plasma. The higher the injection velocity, the larger is the size of the inflated magnetic bubble. It is seen that the original magnetic field, which decreases as R−3, is stretched to the extent where it falls as R−α, where R is the distance from the center of the solenoid and α is found in the range 1 ≤ α ≤ 2.; We have also demonstrated that when a plasma stream resembling the solar wind interacts with the expanding magnetic bubble, a magnetopause or bow-shock like structure is formed at the interaction region. The bow-shock is first pushed outward by the magnetic field undergoing inflation, but it eventually becomes standstill when the magnetic pressure and the plasma stream pressure at the interaction region balance each other with no further inflation in the magnetic field. We see accumulation of the plasma stream particles in the bow-shock while some of them are reflected back also; the piling up and the reflection imply a loss in the plasma stream momentum. This loss in momentum of the plasma stream exerts a force on the magnetic bubble and thus, possibly on the spacecraft.