Transverse emittance and current of multi-GeV trapped electrons in a plasma wakefield accelerator

Multi-GeV trapped electron bunches in a plasma wakefield accelerator (PWFA) are observed with normalized transverse emittance divided by peak current, ϵN,x/It , below the level of 0.2μm/kA . A theoretical model of the trapped electron emittance, developed here, indicates that emittance scales inversely with the square root of the plasma density in the nonlinear “bubble” regime of the PWFA. This model and simulations indicate that the observed values of ϵN,x/It result from multi-GeV trapped electron bunches with emittances of a fewμm and multi-kA peak currents.