Abstract
In radiation pressure dominated laser ion acceleration schemes, transverse target deformation and Rayleigh-Taylor (RT)-like instability always develop quickly, break the acceleration structure, limit the final accelerated ion energy, and lower the beam quality. To overcome these issues, we propose a target design named dual parabola targets consisting of a lateral thick part and a middle thin part, each with a parabolic front surface of different focus positions. By using such a target, through interactive laser and target shaping processes, the central part of the thin target will detach from the whole target and a microtarget is formed. This enables the stable acceleration of the central part of the target to high energy with high quality since usual target deformation and RT-like instabilities with planar targets are suppressed. Furthermore, this target design reduces the laser intensity required to optimize radiation pressure acceleration by more than 1 order of magnitude compared to normal flat targets with similar thickness and density. Two-dimensional particle-in-cell simulations indicate that a quasimonoenergetic proton beam with peak energy over 200 MeV and energy spread around 2% can be generated when such a solid target (with density $400{n}_{c}$ and target thickness $0.5{\ensuremath{\lambda}}_{0}$) is irradiated by a 100 fs long circularly polarized laser pulse at focused intensity ${I}_{L}\ensuremath{\sim}9.2\ifmmode\times\else\texttimes\fi{}{10}^{21}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$.
Highlights
There is increasing demand worldwide for more effective cancer therapy techniques
We propose a target design named dual parabola targets consisting of a lateral thick part and a middle thin part, each with a parabolic front surface of different focus positions
In the case of using a plane target, both transverse target deformation and the development of the Rayleigh-Taylor-like instability are inevitable, which can prevent the formation of a light sail process for effective proton acceleration
Summary
There is increasing demand worldwide for more effective cancer therapy techniques. Among all the known methods, ion beams show incomparable advantages due to their high cure rate and painless treatment, mainly due to its unique sharp Bragg absorption peak. [49], the required laser intensity should be as high as 3:4 Â 1023 W=cm (corresponding to the normalized laser amplitude a % 111:4) To overcome these issues in the RPA process, the use of micro-high-density targets (often called as mass-limited targets with transverse size of tens of micrometers and thickness of a few nanometers) has been suggested theoretically and experimentally [13,48,50]. With such targets, target deformation effects will be largely reduced due to the relative uniform distribution of the local laser intensity. The idea of using specific target curvatures or geometry to optimize laser ion acceleration is not new, e.g., in Refs. [29,51,52,53] based upon the TNSA mechanism, our target design is different essentially in principle as shown below
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