Figure 2

Quasi-3D PIC simulation to show the of density ramp on the LWFA: Figure (a) highlights the initial density profiles used to simulate three cases, and (b) compares the electron energy spectrum for the three cases when the maximum energy is obtained at time \({t}=1452\,{{\omega }}_{{p}}^{-1}\) for case (i) and (ii), and at time \({t}=1313\,{{\omega }}_{{p}}^{-1}\) for case (iii). Figure (c–e) show the longitudinal phase space and electric field lineout at the axis (blue line) for the three cases at time \({t}=1194\,{{\omega }}_{{p}}^{-1}\). The phase space and electric fields are shown at an earlier stage as compared to the spectrum to clearly point out the differences in the electric fields, especially in the case of (i) and (ii).