Density-Customized Capillary (DC2) Discharge

Capillary discharges are used in laser plasma accelerators for providing the plasma medium that both forms the wakefield and guides the laser beam. For the latter, the radial parabolic density profile within the capillary channel can maintain a constant laser focus size along the capillary provided the proper conditions are satisfied between the laser beam waist size, channel diameter, and on-axis plasma density. This is referred to as matched guiding, but achieving this has been elusive and, instead, nonlinear self-focusing is typically utilized to achieve the required laser spot size. The Density-Customized Capillary (DC2) Discharge being developed is designed to enable true matched guiding without relying on nonlinear focusing. Furthermore, the goal is to accomplish this at the relatively low plasma densities needed by experiments, such as for the BErkeley Lab Laser Accelerator (BELLA) program. Our scheme also permits tapering the on-axis density along the capillary while maintaining the same matched spot size. Preliminary experimental results on the DC2 Discharge will be presented as well as demonstration of scaling to 1-meter-long capillary lengths.