  Ion beam has been used in cancer treatment, and has a unique preferable
feature to deposit its main energy inside a human body so that cancer cell
could be killed by the ion beam. However, conventional ion accelerator tends to
be huge in its size and its cost. In this paper a future intense-laser ion
accelerator is proposed to make the ion accelerator compact. An intense
femtosecond pulsed laser was employed to accelerate ions. The issues in the
laser ion accelerator include the energy efficiency from the laser to the ions,
the ion beam collimation, the ion energy spectrum control, the ion beam
bunching and the ion particle energy control. In the study particle computer
simulations were performed to solve the issues, and each component was designed
to control the ion beam quality. When an intense laser illuminates a target,
electrons in the target are accelerated and leave from the target; temporarily
a strong electric field is formed between the high-energy electrons and the
target ions, and the target ions are accelerated. The energy efficiency from
the laser to ions was improved by using a solid target with a fine
sub-wavelength structure or by a near-critical density gas plasma. The ion beam
collimation was realized by holes behind the solid target. The control of the
ion energy spectrum and the ion particle energy, and the ion beam bunching were
successfully realized by a multi-stage laser-target interaction. The present
study proposed a novel concept for a future compact laser ion accelerator,
based on each component study required to control the ion beam quality and
parameters.
