Y. J. Gu

Stable long range proton acceleration driven by intense laser pulse with underdense plasmas

Proton acceleration is investigated by 2.5-dimensional particle-in-cell simulations in an interaction of an ultra intense laser with a near-critical-density plasma. It was found that multi acceleration mechanisms contribute together to a 1.67 GeV collimated proton beam generation. The W-BOA (breakout afterburner based on electrons accelerated by a wakefield) acceleration mechanism plays an important role for the proton energy enhancement in the area far from the target. The stable and continuous acceleration maintains for a long distance and period at least several pico-seconds. Furthermore, the energy scalings are also discussed about the target density and the laser intensity.

Controllable Laser Ion Acceleration

When an intense laser illuminates a target, temporarily a strong electric field is formed, and the target ions are accelerated. The control of the ion energy spectrum and the ion particle energy, the ion beam collimation and the ion beam bunching are successfully realized by a multi-stage laser-target interaction.

Multi-Stage Ion Acceleration in Laser Plasma Interaction

A remarkable ion energy increase is demonstrated by several-stage post-acceleration in a laser plasma interaction. Intense short-pulse laser generates a strong current by high-energy electrons accelerated. The strong electric current creates a strong magnetic field along the high-energy electron current in plasma. During the increase phase of the magnetic field, the longitudinal inductive electric field is induced for the forward ion acceleration. The inductive acceleration and the target-normal sheath acceleration in the multi stages provide a unique controllability of the ion energy and its energy spectrum. By the four-stage successive acceleration, our 2.5-dimensional particle-in-cell simulations demonstrate a remarkable increase in ion energy by a few hundreds of MeV; the maximum proton energy reaches 254MeV.

Large quantity ion beam generation by persistent Coulomb explosion in a near-critical density plasma channel

The mechanism of Coulomb explosion induced by the interactions of ultra-intense laser pulses with near-critical density plasmas was investigated using 2.5D particle-in-cell simulations. While the Coulomb explosion occurred continuously during pulse propagation inside the plasma, a large quantity of charge was generated and acquired in the backward direction. The accelerated ion beam had a peak energy of several tens of MeV, and the maximum energy was over hundreds MeV. A theoretical model has been proposed to estimate the total acquired charge quantity, the maximum ion energy, and their dependence on the initial plasma density.

Enhancement of proton acceleration field in laser double-layer target interaction

A mechanism is proposed to enhance a proton acceleration field in laser plasma interaction. A double-layer plasma with different densities is illuminated by an intense short pulse. Electrons are accelerated to a high energy in the first layer by the wakefield. The electrons accelerated by the laser wakefield induce the enhanced target normal sheath (TNSA) and breakout afterburner (BOA) accelerations through the second layer. The maximum proton energy reaches about 1 GeV, and the total charge with an energy higher than 100 MeV is about several tens of μC/μm. Both the acceleration gradient and laser energy transfer efficiency are higher than those in single-target-based TNSA or BOA. The model has been verified by 2.5D-PIC simulations.

Laser guiding plasma channel formation criterion in highly relativistic regime

Self-formed plasma channels induced by ultra-intense and ultra-short laser pulses have been investigated with 2.5-dimensional particle-in-cell simulations. A criterion of channel formation under the highly relativistic regime is proposed and tested by simulation results. Good matches between criterion predictions and simulations are found in most cases, but small deviations occur when the plasma density is very low or near critical. The possibility of generating a channel by a femtosecond pulsed laser is also discussed.

Electron self-injection into the phase of a wake excited by a driver laser in a nonuniform density target

It is well known that if electrons are externally injected into a density upramp, then their dephasing lengths will be extended greatly, and thus these electrons will gain more energy. However, we find that a density upramp can also be used to control the beams collimation and the emittance that occurs by self-injection in the gradient. When electrons self-inject into the wakefield in a density gradient, an electron filtering mechanism is found to occur in the injection process. Electrons with high transverse velocities are scattered and only electrons with high longitudinal to transverse velocity ratios can be candidate electrons for self-injection. This causes the trapped electrons to be more highly collimated. In addition, the injection occurs near the axis, which causes the accelerated electron beam to have reduced emittance. An ultra-collimated electron beam with an angle spread of ∼1° and emittance of ∼0.01 mm mrad is generated by a 2.5-dimensional particle-in-cell (2.5-D PIC) simulation.

Controllable laser ion beam generation

In intense-laser plasma interaction, several issues still remain to be solved for a future laser particle acceleration. In this paper we focus on a bunching of ion beam, which is preaccelerated by a strong electric field generated in a laser plasma interaction. In this study, a nearcritical-density plasma target is illuminated by an intense short laser pulse. A moving strong inductive electric field is generated inside of the target. We have successfully obtained a bunched ion beam in our particle-in-cell simulations in this paper.

Collimation of laser-produced proton beam

In intense laser plasma interaction for particle acceleration several issues remain to be solved. In this paper we focus on a collimation of ion beam, which is produced by a laser plasma interaction. In this study, the ion beam is collimated by a thin film target. When an intense short pulse laser illuminates a target, target electrons are accelerated, and create an electron cloud that generates a sheath electric field at the target surface. Such the ion acceleration mechanism is called the target normal sheath acceleration (TNSA). The TNSA field would be used for the ion beam collimation by the electric field. We have successfully obtained a collimated beam in our particle-in-cell simulations.

Ion beam control in laser plasma interaction

By a two-stage successive acceleration in laser ion acceleration, our 2.5-dimensional particle-in-cell simulations demonstrate a remarkable increase in ion energy by a few hundreds of MeV; the maximum proton energy reaches about 250MeV. The ions are accelerated by the inductive continuous post-acceleration in a laser plasma interaction together with the target normal sheath acceleration and the breakout afterburner mechanism. An intense short-pulse laser generates a strong current by high-energy electrons accelerated, when an intense short- pulse laser illuminates a plasma target. The strong electric current creates a strong magnetic field along the high-energy electron current in the plasma. During the increase phase in the magnetic field strength, the moving longitudinal inductive electric field is induced by the Faraday law, and accelerates the forward-moving ions continously. The multi-stage acceleration provides a unique controllability in the ion energy and its quality.