Examination of the acceleration mechanisms for relativistic electron generation in an underdense, laser-driven plasma in the picosecond regime*

Energetic electrons accelerated through intense laser-plasma interactions are useful for driving secondary particle and radiation sources such as ions, x-rays, and neutrons. Depending on the laser and solid target plasma conditions, electrons can be accelerated by several mechanisms such as target normal sheath acceleration, hole boring, break-out afterburner, or direct laser acceleration, each resulting in electron spectra with its own defining characteristics. To study these mechanisms, we performed experiments on the Vulcan Target Area West (TAW) laser at the Rutherford Appleton Laboratory’s Central Laser Facility, exploring the dynamics of high-intensity laser pulses with picosecond pulse durations irradiating short plasma channels of varying density. This regime is of particular interest to experiments utilizing solid density targets where the laser pre-pulse creates a sub-critical plasma in which electrons can be accelerated to high energies in a short distance. To better understand the different acceleration mechanisms, we investigated key components of the laser-plasma interaction, including plasma density and channel length, and studied their impact on the energy gain and angular spread of accelerated electrons.