Electron Acceleration Based on an Elongated Plasma Channel

Experiments for the laser guiding studies has been carried out with the 30-fs 100-TW Ti:sapphire laser pulse interaction with the underdense plasma produced by a long-slab (1.2 times 10 mm²) gas jet and an ablative laser-triggered discharged capillary. Formation of an extremely long plasma channel with a length (~10 mm) 10 times above the Rayleigh length is observed when the laser pulse power is much higher than the critical power for relativistic self-focusing. The long-self-guiding- channel formation is accompanied by the electron acceleration with a low transverse emittance (< 0.87pi mm mrad) and high electric current (~10 nC/shot), as well as the generation of a quasi- monoenergetic electron bunch with an energy of ~80 MeV. In order to continuously elongate the plasma channel, a 4-cm- scale discharged capillary was used. We successfully demonstrated laser-plasma acceleration of high-quality electron beams up to nearly semigigaelectronvolts. Our results exactly verified the prediction of laser wakefield acceleration through a centimeter- scale plasma channel in the "blowout bubble" regime, where a microscale plasma cavity produced through the ultrarelativistic laser-plasma interactions plays an essential role in the self- injection and acceleration of electrons.