Self-generated magnetic collimation mechanism driven by ultra-intense LG laser

Abstract

Collimation control of energetic plasma beams is crucial in the laser–plasma field. In this paper, we report on a self-collimated acceleration scheme for a plasma beam using an ultra-intense Laguerre–Gaussian (LG) laser irradiating a solid target. Three-dimensional (3D) particle-in-cell simulations show that a plasma beam with a high current density is stably formed by the radiation pressure of the hollow LG laser. The initial interaction of LG laser with solid target can be approximately researched by a deformable mirror model. Under the effect of the ponderomotive force of the LG laser, the plasma converges in the center axis to form a narrow beam. An elongated strong-magnetic tunnel (B ∼ 2 kT) is self-generated around the plasma beam, capable of trapping some electrons in a region with a radius of less than 500 nm (r < 500 nm). Compared with the case driven by the conventional Gaussian laser, the beam radius size is dramatically reduced from the microscale to hundreds on the nanoscale. The beam density is increased by at least ten times. Such an interesting scheme can provide a feasible and efficient way to achieve and enhance the collimation of energetic particle beams, which may benefit the general applications of fast ignition in inertial fusion, radiotherapy, realization of high-energy density states, and so on.

Optimal collimation of proton beams accelerated by a Laguerre–Gaussian laser with a proper pulse duration

“…However, D ≪ γm e vθ/2B φ e is obtained for B φ = 33.41 T and D = 0.8 µm according to equation (3), indicating that the plasma cannot be collimated within the region of D < 0.8 µm using a traditional Gaussian laser (figure 4). Figure 4(d) shows that the strength of the self-generated magnetic field is significantly reduced under large laser pulse duration (t pulse = 300 fs) because, in this case, the protons have sufficient time to catch up with the compressed electron layer during the hole-boring stage [55]. Thus, the net current of the plasma jet is extremely low and cannot generate an intense self-generated magnetic field.…”

“…and the Larmor radius (r L ) can be calculated using the following equation: Then, the collimation condition for the electrons [55][56][57], with…”