Fig. 1. Setup of the tape target experiment and related diagnostics in the VEGA-3 experimental chamber (see text for details). A picture of the tape target system is also shown.

Fig. 2. Proton maximum cut-off energy for (a) aluminium and (b) copper targets. Degradation of the signal can be observed in both figures and in all detectors. The maximum proton energy found for the aluminium target is around 11 MeV and decreases up to 6 MeV on average, while for the copper target it is around 13 MeV and decreases up to 7 MeV on average. The direct IC detects for both materials a maximum of about μSv/h (not shown). In the case of the moderated IC, it measures 0.8 μSv/h (aluminium) and 1.0 μSv/h (copper). The TOF and TCM signals for copper were lost.

Fig. 3. Measurements of the relative displacement from best focus of the Rayleigh length distance as a function of the maximum proton energies measured in single-shot laser interaction for target position movement (upper figure) and modification of the collimation lens (lower figure). The maximum return current EMP signal measured by the TCM is also shown for the same shots. Each point corresponds to an average of 10 shots with its standard deviation.

Fig. 4. Optimization with (a) target position and (b) laser collimation lens during operation in the copper target. Shot numbers (#) are indicated by red lines. In case (a), the target was moved 3 (#30), 5 (#60), 8 (#90) from the original position to optimize the signal. In (b), the target was moved prior to the run to 8 and then the laser focal spot was moved to 9 (#86) and then to 11 (#115), clearly exceeding the optimum interaction plane. Afterwards the focal spot is moved back to 8 (#153).

Fig. 5. Stabilization of maximum proton signal for aluminium and copper targets. In both cases the target was moved prior to the run to 9. The maximum proton energy found for aluminium target is around 10 MeV at the end of the run, while for the copper target it is around 9 MeV. The energy jumps in (b) cannot be explained and both the IC detectors and TCM do not show sharp differences. The direct IC detector measures a maximum of about μSv/h (aluminium) and μSv/h (copper) (not shown) and the moderated one 1 μSv/h (aluminium) and 0.5 μSv/h (copper). The maximum return current EMP detected stabilizes around 0.6 kA at the end of the run.

Fig. 6. One-thousand shot run of 0.8 PW at 1 Hz. The target was moved prior to the run to 9; then the laser focal spot was moved to 5 (#423), 7 (#475) and back to 9 (#502). The signal is stable at 10 MeV (TPS) and 6 MeV (TOF detector). The direct IC detector measures a maximum of about μSv/h (not shown) and the moderated one 0.8 μSv/h. The TCM measures an almost stable 0.75 kA return current EMP.