Magnetic-field-induced enhancement of ion beam energy in a magnetically expanding plasma using permanent magnets

Ion energy distribution functions (IEDFs) near a source exit of a magnetically expanding argon plasma using only permanent magnets (PMs) are measured by a combination of a retarding field energy analyzer and a pulsed probe method for three types of magnetic-field configurations and various operating gas pressures, where the magnetic-field strength in the source tube is increased up to 270 G by adding the number of the PM layers. The 13.56 MHz rf power for plasma production is maintained at 250 W. The IEDFs show the existence of an accelerated group of ions. It is found that the energy of the accelerated ions increases when the magnetic-field strength is increased, but saturates at seven times the electron temperature at argon pressures of 0.6-1.6 mTorr. Our results show that the maximum velocity of the accelerated ions is found to be 14 km s^-1 with a Mach number of 3.8.