So, assume you have a plasma in a vacuum made of an even distribution of 50% electrons and 50% protons all flowing in one direction with low collision frequency. Then you suddenly turn on an external magnetic field and watch what happens. How will the plasma react? Will the magnetic field lines cause currents that will cancel the magnetic field out within the plasma? Will the electrons and protons start going in circles in opposite directions? Will the plasma redistribute into currents that align with the magnetic field? Will something else happen?