Fig. 3
Trapping conditions for the electron beam. Snapshot of the fields and longitudinal phase-space of the extracted electrons at simulation time t = 2.103 ps, where the pulses are at their focus point in the center of the first target section. In panel (a) the particles extraction is depicted along with the on-axis line-out of the normalized electric fields components. The horizontal dashed-dot green line represents the saturation threshold for the extraction \(Ar^{8^+\rightarrow 9^+}\) from the driver pulses. The black and red dashed line show the saturation threshold for \(Ar^{9^+\rightarrow 10^+}\) and \(Ar^{10^+\rightarrow 11^+}\) from the ionization pulse, respectively. The vertical gray and red bands show the approximate original position of the \(Ar^{9^+\rightarrow 10^+}\) and \(Ar^{10^+\rightarrow 11^+}\) extracted electrons. In panel (b) the trapping condition in emphasized. There, the normalized potentials and the accelerating gradient are shown. The available extraction region which allows for further weak (strong) particle trapping is emphasized with the vertical green (red) band. As a combined result, only the electrons extracted by the ionization pulse will be further accelerated. (c) and (d) Fields and electron beam evolution along target. The first and second sections density profiles are shown in green and gray, respectively. (a) Total pulse energy (orange) and peak normalized evolution (blue). The right (red) axis shows the evolution of the averaged normalized longitudinal electric field on the beam \(\langle E_z\rangle /E_0\). (b) Electron beam average energy (black), rms energy spread (orange) and brightness 6D (blue) evolution. The right (red) axis shows purely transverse quantities as the normalized emittances along x and y as (full lines) long as the beam transverse size (dashed line).
