Multidipole confinement and the magnetic vector potential

A computer model is used to find individual electron and ion trajectories in an idealized multidipole device modeled as an infinitely long cylinder with surface linear dipoles of 30 mT oriented axially. The electromagnetic momentum of the magnetic vector potential at the wall qA prevents direct loss when it exceeds the mechanical momentum mv of particles originating from regions of negligible vector potential. Primary electrons (80 eV) originating near the axis have many bounces from the high field region before being lost to the wall near a dipole axis where qA = 0. Thermal electrons created near the cylindrical axis have irregular orbits characterized by bounces from walls, but those created near the walls (mv < qA) may be mirror confined. Argon ions accelerated by the plasma potential (mv ≫ qA) have only small deflections by the dipolar fields and are lost in a single pass to any region of the wall. Confinement of lighter helium ions becomes possible with dipolar fields increased in strength by an order of magnitude, creating qA > mv at the walls.