Effect of ion cyclotron motion on the structure of wakes: A Vlasov simulation

The global structure of wake fields behind an unmagnetized object in the solar wind is studied by means of a 2.5-dimensional full electromagnetic Vlasov simulation. The interaction of a plasma flow with an unmagnetized object is quite different from that with a magnetized object such as the Earth. Due to the absence of the global magnetic field, the unmagnetized object absorbs plasma particles which reach the surface, generating a plasma cavity called a wake on the anti-solar side of the object. The interaction between the solar wind with an out-of-plane interplanetary magnetic field and an unmagnetized object of ion-gyro scale is examined to study the effect of the ion cyclotron motion on the structure of wake fields. It is shown that the wake boundary layer is broadened when the inner product of the electric force and the density gradient of the wake boundary layer is negative. On the other hand, a steep wake boundary layer is formed with a negative inner product. The result suggests that the structures of wake fields become asymmetric due to the in-plane E cross B drift motion of ions.