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Ion beams are useful for medical ion beam cancer therapy, basic particle physics, controlled nuclear fusion, high-energy sources, and so on. 1-10) Present conventional ion accelerators are huge in its size and its cost. On the other hand, a higher laser intensity has been realized by the chirped pulse amplification, and intense pulsed lasers are now available for experiments and applications. The energy of ions, which are accelerated by an interaction between the intense laser pulse and a gas target, reaches over a few tens of MeV. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25] The issues in the laser ion acceleration include an ion beam collimation, 10,11,15) Background: 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. Subjects and methods: 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. Results: 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. Conclusions: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.

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A remarkable ion energy control is demonstrated by several-stage post-acceleration in a laser plasma interaction. Intense short-pulse laser generates a strong current by high-energy electrons accelerated. The strong electric current creates a strong magnetic field. During the increase phase of the magnetic field, the longitudinal inductive electric field is induced for the forward ion acceleration. The inductive acceleration and the target-normal sheath acceleration in the multi stages provide a unique controllability of the ion energy and its energy spectrum. By the four-stage successive acceleration, our 2.5-dimensional particle-in-cell simulations demonstrate that the maximum proton energy reaches 254MeV.

An ion beam has the unique feature of being able to deposit its main energy inside a human body to kill cancer cells or inside material. However, conventional ion accelerators tend to be huge in size and cost. In this paper, a future intenselaser ion accelerator is discussed to make the laser-based ion accelerator compact and controllable. 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, each component is designed to control the ion beam quality by particle simulations. The energy efficiency from the laser to ions is improved by using a solid target with a fine sub-wavelength structure or a near-critical-density gas plasma. The ion beam collimation is performed by holes behind the solid target or a multi-layered solid target. The control of the ion energy spectrum and the ion particle energy, and the ion beam bunching are successfully realized by a multi-stage laser-target interaction.