Numerical studies of acceleration of thorium ions by a laser pulse of ultra-relativistic intensity

摘要

One of the key scientific projects of ELI-Nuclear Physics is to study the production of extremely neutron-rich nuclides by a new reaction mechanism called fission-fusion using laser-accelerated thorium (~(232)Th) ions. This research is of crucial importance for understanding the nature of the creation of heavy elements in the Universe; however, they require Th ion beams of very high beam fluencies and intensities which are inaccessible in conventional accelerators. This contribution is a first attempt to investigate the possibility of the generation of intense Th ion beams by a fs laser pulse of ultra-relativistic intensity. The investigation was performed with the use of fully electromagnetic relativistic particle-in-cell code. A sub-μm thorium target was irradiated by a circularly polarized 20-fs laser pulse of intensity up to 10~(23)W/cm~(2), predicted to be attainable at ELI-NP. At the laser intensity ~ 10~(23)W/cm~(2)and an optimum target thickness, the maximum energies of Th ions approach 9.3 GeV, the ion beam intensity is > 10~(20)W/cm~(2)and the total ion fluence reaches values ~ 10~(19)ions/cm~(2). The last two values are much higher than attainable in conventional accelerators and are fairly promising for the planned ELI-NP experiment.