Analytical and numerical studies of underdense and overdense regimes in plasma-dielectric wakefield accelerators

We present the results of analytical studies and numerical simulations of a plasma-dielectric wakefield accelerator (PDWFA). The plasma-dielectric structure under investigation is a dielectric-lined circular waveguide that has a transport channel filled with isotropic plasma. In the linear theory approximation (overdense plasma) the total field is represented as a sum of the plasma wave, the eigenwaves of the dielectric waveguide, and the quasistatic field of the bunch. It is shown that at a certain plasma density the superposition of the plasma wave and the dielectric waves allows the acceleration of the witness bunch by the field of the dielectric wave together with simultaneous focusing by the plasma wave. For the overdense plasma regime the results of analytical investigations coincide well with results of particle-in-cell (PIC) simulations. Also, we carried out a PIC simulation of the underdense (blowout) regime of wakefield excitation in the unit. In this regime a focusing is provided by ions remaining in the drift channel after pushing out from it plasma electrons.