Positron acceleration via laser-augmented blowouts in two-column plasma structures.

We propose a setup for positron acceleration consisting of an electron driver and a laser pulse creating a twofold plasma column structure. The resulting wakefield is capable of accelerating positron bunches over long distances even when the evolution of the driver is considered. The scheme is studied by means of particle-in-cell simulations.

Efficient Narrow-Band Terahertz Radiation from Electrostatic Wakefields in Nonuniform Plasmas.

It is shown that electrostatic plasma wakefields can efficiently radiate at harmonics of the plasma frequency when the plasma has a positive density gradient along the propagation direction of a driver. The driver propagating at a subluminal group velocity excites the plasma wakefield with the same phase velocity. However, due to the positive density gradient, the wake phase velocity steadily increases behind the driver.