Elongation of plasma channel for electron acceleration

Experiments for the laser guiding studies has been carried out with the 30 fs, 100 TW Ti:Sapphier laser pulse interaction with the long slab (\textit{1.2x10 mm}$^{2})$ and discharged capillary of underdense plasma. Formation of extremely long plasma channel with its length (\textit{$\sim $ 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 quasi-monoenergetic electron acceleration with a low transverse emittance (\textit{$<$ 0.8 $\pi $ mm mrad}) and high electric current (up to \textit{$\sim $ 10 nC/shot}). In order to continuously elongate plasma channel, a 4 cm-scale discharged capillary was used. We successfully demonstrated laser-plasma acceleration of high-quality electron beams up to nearly GeV. Our results exactly verified the prediction of laser-wakefield acceleration through a cm-scale plasma channel in the ``blowout bubble'' regime, where a micro-scale plasma cavity produced through the ultra-relativistic laser-plasma interactions plays an essential role in the self-injection and acceleration of electrons.