Generation of Monochromatic Laser-accelerated proton beam: Numerical study

The advent of ultra-intense laser pulse and its rapid development has opened up a new regime of science called relativistic plasma. This regime has been attracted due to not only its fundamental physical interest but also its wide application such as high energy particle and radiation generation. The laser-accelerated ion beam has several advantages over a conventional accelerator such as compact size, energy tunability, which make it feasible using in injection into conventional accelerators, the fast ignition of thermonuclear target, and hadron therapy in oncology. The synchronization of the accelerated proton beam with driving laser pulse also makes it possible the measurement of plasma dynamics with high temporal resolution. For the application to the hadron cancer therapy, the laser-accelerated proton beam should meet several requirements, which are energy (a few 10 . 150 MeV), number (1010-5x1015/sec), and energy spread (ΔE/E≤2%). The first requirements have been experimentally demonstrated and the second condition awaits just the appearance of high repetition laser. However the proton spectra obtained in laser-plasma experiments shows wide energy distribution with cutoff energy while in case of electron acceleration much progress has been made. Thus to fulfill the requirements for the hadron cancer therapy, much efforts should be devoted to the enhancement of the monochromacity of the proton energy distribution. Recently a scheme utilizing double-layer target was proposed for the generation of high-quality laser accelerated proton beams. And energy spread less than 5 % was obtained by an intensive three-dimensional PIC (Particle-In-Cell) simulation. Adopting such an idea, one- and 2-dimensional PIC simulation was performed to investigate the characteristics of the accelerated proton beam in an experimental parameter space