Proton Beam Generated in PW Laser Interaction With Nano-Structure Array for Proton Therapy

Abstract

In comparison with large and expensive conventional linear and circular accelerator, miniaturized laser-driven proton accelerator provides the potential to reduce the overall costs. This could allow a widespread use of the superior properties of protons and ions in radiation therapy. However, the key to success is to improve the particle energy which is not high enough to meet the requirement for the treatment. With the development of high-repetition-rate petawatt class laser technology matures gradually, different acceleration mechanisms have been able to raise the energy of protons to close to 100MeV.To confirm the feasibility of proton beam generated in petawatt-laser irradiating nano-array target, three-dimensional particle-in-cell (3D-PIC) simulations were performed with the QED-PIC code EPOCH. The simulation box has a size of 30 μm(x) × 20 μm (y) × 20 μm (z), which is sampled by cells of 1500 × 400 × 400 with 125 pseudo-electrons, eight pseudo-carbons, and four protons in each cell. The Gaussian laser pulse propagates along the x-direction with y-direction polarization, a wavelength λ0 of 1μm, a peak power of 50 PW, and a duration of 30 fs in full width at half maximum (FWHM). With an initial focal spot radius σ = 3μm. In order to reduce the computational requirements. The array wires have an initial density of ne = 300nc (where nc = 1.1 × 1021 cm-3 is the critical plasma density) and are attached to a 4-μm-thick CH foil. In these simulations, periodic boundary conditions were employed for the laser field in the transverse directions and absorbing boundary conditions for the particles.Three-dimensional particle-in-cell simulation show that the laser-driven proton beam keep quite different characteristics compared with other accelerators proton beam, such as ultra-short beam duration (ns), high strength (107 / cm2 / pulse), large divergence angle (2°) and poly real-energetic spectrum. Meanwhile, we show that under optimal interaction conditions protons can be accelerated up to relativistic energies of 300 MeV by a petawatt laser field. The proton acceleration is due to the dragging Coulomb force arising from charge separation induced by the ponderomotive pressure ∼light pressure! of high-intensity laser.We investigate the impact of nano-structure array on the proton spectrum for different laser-plasma conditions. Our simulated data show that the nanostructures lead to a significant enhancement of absorption over the entire range of laser plasma conditions investigated. At conditions that do not allow for efficient laser absorption by plane targets, nano-structure array is found to significantly enhance the proton cut-off energy and conversion efficiency.S. Wu: None. Z. Wang: None. X. Sun: None. W. Wang: None. F. Xiao: None. L. Zhao: None.