Ion acceleration in a solenoid-free plasma expanded by permanent magnets

Ion acceleration is achieved in a low-pressure solenoid-free plasma expanded by permanent magnet arrays. Although a permanent magnet normally forms cusp magnetic fields which prevents plasma diffusion and double layer formation, by employing double concentric arrays of permanent magnets, a constant field area, and a diverging magnetic field can be generated near the outlet of the plasma source. In the source, a rapid potential drop with 4 cm thickness from 50 V to 20 V is generated at the diverging field area for 0.35 mTorr and a supersonic ion beam accelerated through the potential drop is observed in the diffusion chamber. The beam energy can be increased up to over 40 eV with a decrease in gas pressure.