On time-of-flight ion energy deposition into a metal target by high-intensity pulsed ion beam generated in bipolar-pulse mode

The energy deposition of high-intensity pulsed ion beam (HIPIB) into a titanium target was studied in TEMP-6 apparatus of bipolar-pulse mode using a self-magnetic field magnetically insulated ion diode (MID), where anode plasma was pre-generated by a first negative voltage and then mixed carbon ions and proton beam was extracted during the positive stage of the bipolar pulse. According with the time-of-flight (TOF) of ions, C+ arriving at the target 14 cm downstream from the MID was delayed by 55 ns relative to H+ at a peak accelerating voltage of 250 kV and the ion energy spectrum varied greatly, starting with a Gaussian profile at exit of MID and arriving with a multi-energy complex distribution. The TOF ion energy deposition of HIPIB showed that the energy deposition proceeded firstly in a deeper depth delivered by H+ and then moved towards a top layer dominated by C+. It is found that, the contribution of H+ to the energy deposition is negligible at the beam composition of 70%C+ and 30%H+. As a result, the gradient of energy deposition profile in target is negative by C+ deposition through the whole pulse. This unique feature of HIPIB energy deposition can lead to different thermal and dynamic effects as compared to previous studies of H+-abundant HIPIB, electron or laser beam, especially limiting subsurface heating that is concerned as a major cause of droplet ejection and surface cratering and waviness formation.