PHYS-E0461 - Introduction to plasma physics for fusion and space applications D, Lecture, 13.9.2021-15.12.2021

Let’s consider the significance of Earth’s magnetic field on Earth’s surface. Put an electric charge in between two capacitor plates that produce a strong electric field with straight field lines perpendicular (East-West) to the prevailing (weak) Earth’s magnetic field. According to common sense (and experience), the particle is accelerated towards one of the plates. However, during the lectures we learned that if the particle experiences electric and magnetic fields perpendicular to each other, it moves in direction perpendicular to both fields, i.e., up or down in this case! What makes things even stranger is that the magnitude of the drift is given by E/B, i.e., it is particularly strong for LOW magnetic fields. Consider carefully the motion of the particle and show that there is no contradiction and the particle follows the electric field.