Fig. 1. Transverse normalized emittance evolution along a drift of 1 m downstream of the LWFA source simulated by PIC code (red solid line) and ASTRA code (blue solid line), as well as the theoretical normalized emittance according to Eq. (3) (black dotted line). The simulated trace-space emittance ϵ multiplied by the average relativistic energy factor 〈γB〉 is shown for comparison (green solid line).

Fig. 2. Layout of the experimental setup for the LWFA-driven beam transport line. Two-stage gas jets are magnified in the dashed box. (a) Typical focused beam profile obtained on the removable phosphor screen (S2) with a peak central energy of 500 MeV. (b) Typical energy spectrum of one e beam obtained on S1 before manipulation with main peak central energy, rms relative energy spread, and rms divergence of 515 MeV, 1.1%, and 0.24 mrad, respectively. (c) Typical energy spectrum of one e beam obtained on S3 after manipulation with main peak central energy, rms relative energy spread, and rms divergence of 517 MeV, 0.9%, and 0.06 mrad, respectively.

Fig. 3. Peak energy (blue) and energy spread (red) measured on S1 against accelerating length. The error bars represent the statistical discrepancy in each direction.

Fig. 4. Raw beam patterns recorded on S2 with different e-beam energies and the corresponding electron spectra on S1. (a) Typical 500 MeV beam pattern without manipulation after 10.3 m free-vacuum drift. (b)–(f) Manipulated beam patterns after 10.3 m with mean peak energies of 250, 340, 380, 470, and 515 MeV, respectively. The EMQ parameters are established for 500 MeV e beams.

Fig. 5. Tracking simulations of the beam line for experimental beams. (a) Evolution of the horizontal (upper lines) and vertical (lower lines) beam sizes along the longitudinal propagation with the corresponding central energies for beams shown in Figs. 4(b)–4(f). The shading bands represent the energy spreads. The lattices of the quadrupoles are represented by the blue boxes. (b), (c) Simulated transverse divergence and size at the end of the line as a function of electron energy. The colored shading bands denote the beam energy with corresponding spreads in Figs. 4(b)–4(f).

Fig. 6. False color images observed on S2. (a) Sum of 29 consecutive 500 MeV e-beam profiles and the central positions of each shot (black circles) in free vacuum. (b) Sum of 24 consecutive 500 MeV e beams and the central positions (red circles) with the system of focusing lenses.