Magnetically insulation of the ion diode used for high-intensity pulsed ion beam

Abstract

The effect of magnetic field on the characteristics of high-intensity pulsed ion beam (HIPIB) is investigated on the magnetically insulated mode of external-magnetic field MID in a TEMP-6 type HIPIB apparatus. Without magnetic field, the perveance P ( P = I( t)/[ V( t)] 3/2) increases rapidly after the plasma production in the ion diode, indicating the short of the diode caused by the plasma fast moving in the diode. As the magnetic field increases from 1.1 B crit to 1.7 B crit , the perveance P increases slowly, and the diode current decreases with increasing ion current density, extracted ion current and production efficiency of ion beam due to the effectively suppressed plasma flow in the diode. The ion current density of 350 A/cm 2, diode current of 37 kA and the production efficiency of ion beam of about 30% are obtained with the magnetic field at 1.7 B crit . The perveance P increases more slowly with the magnetic field increasing to 2 B crit , and the ion current density falls to 190 A/cm 2 with the decreased diode current of 24 kA, and the decreased extracted ion current of 7 kA, whereas the production efficiency of ion beam is similar to that of 1.7 B crit caused by excessively inhibited flow of the plasma in the diode. The magnetic field of 1.7 B crit of the external-magnetic field MID in the TEMP-6 type HIPIB apparatus leads to the most efficient output of HIPIB with ion current density of about 350 A/cm 2, diode current of 37 kA, extracted ion current of 11 kA, and the production efficiency of ion beam of about 30% at a peak pulse voltage of 420 kV and an accelerating voltage of 350 kV with a pulse width of 70 ns (full width at half maximum) for surface modification of materials.