Mianzhen Mo

Giga-electronvolt electrons due to a transition from laser wakefield acceleration to plasma wakefield acceleration

We show through experiments that a transition from laser wakefield acceleration (LWFA) regime to a plasma wakefield acceleration (PWFA) regime can drive electrons up to energies close to the GeV level. Initially, the acceleration mechanism is dominated by the bubble created by the laser in the nonlinear regime of LWFA, leading to an injection of a large number of electrons. After propagation beyond the depletion length, leading to a depletion of the laser pulse, whose transverse ponderomotive force is not able to sustain the bubble anymore, the high energy dense bunch of electrons propagating inside bubble will drive its own wakefield by a PWFA regime. This wakefield will be able to trap and accelerate a population of electrons up to the GeV level during this second stage. Three dimensional particle-in-cell simulations support this analysis and confirm the scenario.

Generation of GeV energy electrons from laser wakefield acceleration via ionization induced injection

Summary form only given. Laser wakefield acceleration (LWFA) is a promising approach to realize table-top accelerators. The injection process into the wakefield bubble to some extent determines the charge, divergence, energy gain as well as the energy distribution of the accelerated electrons. Traditionally, self injection using pure helium or hydrogen gas as the interaction medium was employed to accelerate the electrons. However, very high laser powers are required to achieve self injection at the low densities which are compatible with acceleration to GeV energies. Recently, a new technique, ionization induced injection, which takes advantage of the large ionization potential difference between the inner and outer shell electrons of trace atoms in the plasma, has been demonstrated to generate electron beams beyond 1 GeV at lower threshold laser powers than self injection would require [1].

Characterization of MeV electron generation using 527nm laser pulses for fast ignition

Summary form only given. Fast Ignition [1] holds the promise of improved efficiency and reduced laser energy requirements for Laser Fusion Energy systems. The main approach proposed to date is by coupling a beam of 1 to 2 MeV electrons from the laser interaction spot to a 40 micron spot in the compressed fuel core using a metal cone insert to get close to the compressed core [2]. However, multi-millijoule level laser prepulse can create extended preplasmas within the cone, effectively moving the electron generation source region far back from the cone tip and core [3]. By employing second harmonic pulses much reduced levels of prepulse can be achieved and at the same time colder electron distribution can be obtained, closer to those required ultimately for Fast Ignition.