Ion source diodes with magnetic mirror

This device includes a grid anode, a first cathode set in front cf the anode, and a magnetic mirror behind the anode. It is a winding coaxial to the anode and the cathode. Anode and cathode have spherical cap shapes whose concavity is directed towards a target. Then the ion beam has some focusing. Electrons, emitted by cathode, are accelerated towards the anode and cross through it. These electrons are submitted to the winding magnetic field. Their trajectories curved around the field lines and lie on the diode axis. Then electrons go backwards through again the anode. Electrons oscillate thus a great number a time. At each passage, they give energy to the anode, that creates plasma round it. Ions are extracted from that plasma and accelerated by interelectrode field. As there is no electric field in the back of the anode, there is an ion beam emitted only foreward