Linearly tapered discharge capillary waveguides as a medium for a laser plasma wakefield accelerator

Gas-filled capillary discharge waveguides are commonly used as media for plasma wakefield accelerators. We show that effective waveguides can be manufactured using a femtosecond laser micromachining technique to produce a linearly tapered plasma density, which enables the energy of the accelerator to be enhanced significantly. A laser guiding efficiency in excess of 82% at sub-relativistic intensities has been demonstrated in a 40mm long capillary with a diameter tapering from 320 mu m to 270 mu m, which gives rise to an on-axis, time-averaged plasma density that varies from 1.0 x 10(18) cm(-3) to 1.6 x 10(18) cm(-3). (C) 2012 American Institute of Physics. [doi: 10.1063/1.3674309]