Experimental study on capillary discharge for laser plasma wake acceleration

Abstract

Preformed plasma channels play important roles in many applications, such as laser wakefield acceleration, plasma lens, and so on. Laser pulses can be well guided when the radial density distribution of the plasma channel has a parabolic profile and it is matched with the laser focus. Discharging a gas-filled capillary is a possible way to form such plasma channels. In this work, we report the capillary discharging and laser guiding experiments performed in the Laboratory for Laser Plasmas at Shanghai Jiao Tong University. The plasma density distributions in the Helium-filled discharged capillary are measured by using the spectral broadening method. In a capillary with a length of 3 cm and a diameter of 300 μm, the plasma density profile is observed to be uniformly distributed along the axial direction and have a parabolic profile along the radial direction. Parameters for plasma channel generation are scanned. The deepest channel depth obtained is 28 μm, which is close to the focal spot radius of the laser used in the experiment. Laser guidance in the plasma channel is also studied. The results show that the laser can maintain its focus and continuously propagate when the channel depth matches the focal spot, indicating that the well guiding of the laser pulse by the preformed plasma channel is obtained. These studies may serve as the ground work for the future studies, such as staged laser wakefield acceleration and phase-locked wakefield acceleration.