Analysis of the collimation of an electron beam in a Magnetic Mirror for Possible Plasma Thruster Applications

In this paper, we study the dynamics of an electron beam inside a magnetic bottle when a constant electric field parallel to the bottle axis is applied, we use Particle-in-Cell (PIC) simulations with a 1D-3V model in z direction. It is considered that the electron beam has a temperature of 1 eV and follows a Maxwellian distribution function. We study two different cases. In the first case, the electron beam is injected inside an annular device which consists of two stages. In the first stage, called the acceleration stage, the electrons are accelerated by a constant electric field parallel to the bottle axis for a distance equal to half the total length of the annular channel of the device. Then, the accelerated electrons enter a magnetic bottle in order to control the beam divergence and reduce its mobility perpendicular to the magnetic field. This stage is called the collimation stage. In this stage, we consider the force exerted by the magnetic field gradient on the electrons. For the second case, we study the response of the electrons when the electric field and the magnetic bottle span the entire length of the annular channel. In both cases, the electric and magnetic fields point in z direction. For simplicity, we do not consider the electric fields that could be generated by charge separation or density gradients. Finally, we also study the behavior of those electrons that fulfilled the reflection condition and are trapped between both fields.