Investigation On The Shot-to-shot Stability And Characteristics Of Geometrically Focused High-intensity Pulsed Ion Beam

High-intensity pulsed ion beam (HIPIB) technique, originated from inertial confinement fusion (ICF) project, has received extensive attention as a tool for research in materials surface engineering in recent years. The new requirements for applications in material surface engineering urge realiable shot-to-shot stability of HIPIB, which is the key factor that restricts the application. Therefore, The spatial deviations of the HIPIB are evaluated by measuring the energy density distribution by using an infrared diagnostic method considering neutralizing during the ion beam propagation to the focal plane with a spatial resolution of 1 mm. In order to receive stable delay time between the first negative pulse and the second positive pulse, an external triggering mode is applied, which transforms a little power of the first negative pulse to the main-gap to induce the breakdown inside the gap. Correlation of the generation and spread of the HIPIB on the delay time and the pattern in the transportation region are studied as well.Focused high-intensity pulsed ion beam (HIPIB) of 100 ns order pulse is generated with respect to its spatial stability in external magnetically insulated ion diodes (MIDs) with geometrical focusing configuration using the passive anode. Typical energy density per pulse is in the range of 3-6 J/cm2, at an accelerating voltage of 200-300 kV with a pulse duration of 120-150 ns. The spatial deviations of the HIPIB is evaluated by measuring the energy density distribution by using an infrared diagnostic method considering neutralizing during the ion beam propagationto the focal plane with a spatial resolution of 1 mm. The ion beam deviation is about ±1.5 mm for external-magnetic field MID leading to a fluctuation in the energy density of 1-12%. It is confirmed that the displacement of different parts of a beam occurs nonsynchronously mainly attributed to the intrinisic diode processes of plasma generation and expansion, and ion beam extraction from the anode-cathode gap, while the influence of magnetic field in the transportation region is negligible.An external triggering mode is applied, which transforms the high voltage of the first negative pulse to the main-gap to induce the breakdown inside the gap. Consequently, the deviation of breakdown voltage at the output gap and main-gap decrease from 16.3%to 1.20%,15.8% to 1.20%, respetively. The deviation of delay time decreases significantly from 49.1% to 0.41%, which ensures the stability of HIPIB generation. The energy density on the focal plane of ion diode is measured and the results show a fluctuation within 6%. The performed results show that the discharging stability of ion diode has been improved significantly and the reliability of HIPIB is enhanced.The intensity of geometrically focused high-intensity pulsed ion beam from magnetically insulated ion diode is determined mainly by the generation and spread process of plasma on the surface of anode, which is influenced to a great extent by the delay time between the negetive pulse and positive pulse. Initially, the HIPIB density shows a positive correlation to the delay time because the generation and spread of plasma on the surface of anode is strengthened as the delay time increases. When the delay time reaches 450 ns, we receive the highest HIPIB intensity. If we continue to increase the delay time, the intensity drops due to the excessive spread of plasma, which causes the plasma oblivion.