Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Three Dimensional Effects on Proton Acceleration with Grooved Hydrocarbon Targets

Imran Khan, Mohammad Yasir, Vikrant Saxena

TL;DR

This work reveals that three-dimensional groove geometry critically shapes laser-driven proton acceleration. By performing 3D PIC simulations and a waveguide-based analysis, it shows that cylindrical grooves outperform cuboidal ones under linear polarization, achieving proton cut-offs near $\approx 68$ MeV due to enhanced self-focusing and forward electron momentum, whereas cuboidal grooves lag behind. Circular polarization suppresses hot-electron generation and proton energies, with approximately a $15\%$ drop for cylindrical grooves, despite alignment advantages. The results underscore the importance of 3D effects and target geometry for optimizing TNSA-mediated proton beams and have practical implications for target fabrication via laser drilling.

Abstract

Recently, using two-dimensional particle-in-cell simulations, it has been demonstrated that in laser based proton acceleration with micro-structured targets, a single rectangular groove on the target front offers significant proton cut-off enhancement with linearly polarised laser pulses. In the present work, three-dimensional investigations are carried out to identify notable differences between cylindrical and cuboidal groove geometries both of which correspond to a rectangular groove in a two-dimensional case. In particular, a waveguide model is employed to analyse the effect of the groove geometry and extensive three-dimensional particle-in-cell simulations are performed to demonstrate the distinct behaviour of laser pulse and electrons for cylindrical and cuboidal grooves. Further, the effect of a circular polarisation of the incident laser pulse on the spectra of accelerated protons is studied. It is shown that contrary to our initial expectations, cylindrical symmetry and circular polarisation do not play well together and cause as much as 15$\%$ decay in proton cut-off energies as compared to the case of cylindrical symmetry and linear polarisation.

Three Dimensional Effects on Proton Acceleration with Grooved Hydrocarbon Targets

TL;DR

This work reveals that three-dimensional groove geometry critically shapes laser-driven proton acceleration. By performing 3D PIC simulations and a waveguide-based analysis, it shows that cylindrical grooves outperform cuboidal ones under linear polarization, achieving proton cut-offs near MeV due to enhanced self-focusing and forward electron momentum, whereas cuboidal grooves lag behind. Circular polarization suppresses hot-electron generation and proton energies, with approximately a drop for cylindrical grooves, despite alignment advantages. The results underscore the importance of 3D effects and target geometry for optimizing TNSA-mediated proton beams and have practical implications for target fabrication via laser drilling.

Abstract

Recently, using two-dimensional particle-in-cell simulations, it has been demonstrated that in laser based proton acceleration with micro-structured targets, a single rectangular groove on the target front offers significant proton cut-off enhancement with linearly polarised laser pulses. In the present work, three-dimensional investigations are carried out to identify notable differences between cylindrical and cuboidal groove geometries both of which correspond to a rectangular groove in a two-dimensional case. In particular, a waveguide model is employed to analyse the effect of the groove geometry and extensive three-dimensional particle-in-cell simulations are performed to demonstrate the distinct behaviour of laser pulse and electrons for cylindrical and cuboidal grooves. Further, the effect of a circular polarisation of the incident laser pulse on the spectra of accelerated protons is studied. It is shown that contrary to our initial expectations, cylindrical symmetry and circular polarisation do not play well together and cause as much as 15 decay in proton cut-off energies as compared to the case of cylindrical symmetry and linear polarisation.

Paper Structure

This paper contains 8 sections, 1 equation, 10 figures.

Table of Contents

  1. Introduction
  2. Simulation Setup
  3. Analysis
  4. The Waveguide Model
  5. Simulation Results
  6. Linear Polarisation
  7. Circular Polarisation
  8. Discussions and Conclusion

Figures (10)

  • Figure 1: Graphical solution of the eigenvalue equation.
  • Figure 2: cut-off energy evolution for each species for linear polarisation.
  • Figure 3: Electron phase space distribution at t = 60 fs for (top) rectangular groove and (bottom) cylindrical groove.
  • Figure 4: Laser intensity distribution normalized with respect to maximum free space intensity value at t = 60 fs for (top) rectangular and (bottom) cylindrical grooves. The colourbar at the bottom is saturated and higher values are seen in cylindrical case.
  • Figure 5: Particle energy distribution for electrons at t = 90 fs and protons at t = 385 fs.
  • ...and 5 more figures