Optimization of the performance of a laser-plasma accelerator realized with an optical-field-ionized plasma channel*

Laser-plasma accelerators can produce accelerating gradients on the order of tens to hundreds of GV/m, making them attractive as compact particle accelerators for radiation production or high-energy physics applications. Achieving large energy gains requires operating at low plasma densities and guiding the tightly focused laser driver over distances much longer than its characteristic diffraction length. Recently, several schemes for the production of meter-scale plasma waveguides using optical-field-ionization (OFI) techniques have been proposed [1,2]. Compared to waveguides realized with a discharge capillary, which are characterized by a parabolic transverse density profile that extends over distances much larger than the laser spot size, and has ideal guiding properties, the density profile in OFI waveguides has a finite extension with a more complex structure made of a core and a finite-width cladding.  In this work we investigate, analytically and numerically, the propagation of a laser pulse in an OFI waveguide. We study the optimal matching condition that minimizes high-order modes beating, and we evaluate the laser depletion length and group velocity. Finally, the production of multi-GeV electron beams using this type of waveguide is presented.

[1] Shalloo et al., PRE18

[2] Miao et al., PRL20