Speaker
Description
The study of laser wakefield acceleration (LWFA) using long wavelength infrared laser drivers is a promising path for future laser-driven electron accelerators when compared to traditional near-infrared laser drivers operating at $0.8-1$ $\mu\rm{m}$ central wavelength [1,2]. For a fixed laser intensity I, lasers with longer wavelengths $\lambda$ have larger ponderomotive potential ($\propto$ I $\lambda^2$). Stronger wakes can be generated at relatively low laser intensities by using a long wavelength laser driver (i.e. $\lambda=9.2$ $\mu\rm{m}$ CO$_2$ laser) due to its very large ponderomotive potential. LWFA driven by CO$_2$ laser may have significant advantages to applications requiring compact and industrially robust accelerators and radiation sources.
In this work, we use particle-in-cell (PIC) simulations to investigate the self-injection process in CO$_2$ laser-driven wakefield acceleration for various laser and plasma parameters in the blowout regime. PIC code FBPIC [3] is used to extend the results obtained in [1] to model the interaction of a sub-picosecond CO$_2$ laser pulse with wavelength $\lambda=9.2$ $\mu\rm{m}$ and pre-ionized uniform plasma with $a_0$ ranging between 2 and 5. We have explored a wide range of parameters like pulse durations, laser amplitudes, spot size, and plasma densities to determine the self-injection mechanisms through bubble evolution. The accelerating bubble structure of LWFA is dynamic and highly sensitive to the local laser and plasma properties. It can expand and contract as it responds to the evolution of the laser and plasma fields. We report a parameter range that suppresses self-injection in fully blown-out bubbles which is an essential requirement in the experiments of controlled injection in LWFA.
References
[1] Prabhat Kumar, Kwangmin Yu, Rafal Zgadzaj, Michael Downer, Irina Petrushina, Roman Samulyak, Vladimir Litvinenko, and Navid Vafaei-Najafabadi, “Evolution of the self-injection process in long wavelength infrared laser driven LWFA,” Phys. Plasmas 28, 013102 (2021).
[2] Enrico Brunetti1, R. Neil Campbell, Jack Lovell, and Dino A. Jaroszynski, “High-charge electron beams from a laser‑wakefield accelerator driven by a CO$_2$ laser,” Scientific Reports 12, 6703 (2022).
[3] Rémi Lehe, Manuel Kirchen, Igor A. Andriyash, Brendan B. Godfrey, and Jean-Luc Vay, “A spectral, quasi-cylindrical and dispersion-free Particle-In-Cell algorithm,” Computer Physics Communications 203, 66–82 (2016)
Acknowledgments
We acknowledge the support by U.S. Department of Energy, Office of Science under Award No. DE-SC-0014043, DE-SC-0020396, and resources of NERSC facility, operated under Contract No. DE-AC02-5CH11231.
