Fig. 1. (a) Scheme of the experimental setup. For the sake of simplicity, here the diagnostics are plotted in a plane, conserving the angles from the normal direction to the target. In the real setup, diagnostics are arranged at ports located in a spherical chamber. Below each diagnostic, polar () and azimuthal () angles of the corresponding port are reported. (b) Target multilayer structure, consisting of an Al flash coating, a polystyrene layer (CH), a Cu tracer layer and a polyethylene layer (CH), starting from the laser irradiation side. (c) Laser beam configuration in the bundle. Green and blue numbers refer to driver and interaction beams, respectively. Behind the turning mirrors at Ports 1, 3 and 6, the time-integrated optical spectrometer, the optical streak camera and the SRS calorimeter are located, respectively.

Fig. 2. (a) Pinhole camera profiles of the laser spot obtained in shots with (red line) and without (black line) the driver beams. (b) Values of density scalelength L at the quarter of the critical density (green lines) and electron temperature (blue lines) obtained with DUED hydrocode. Time on the x-axis refers to the peak of the interaction pulses. Solid and dashed lines represent conditions obtained without and with the use of the driver beams, respectively.

Fig. 3. Comparison of time-integrated backscattered light spectra measured in shots with (red lines) and without (black lines) the driver beams: (a) /2 emission peaks and (b) SRS spectra.

Fig. 4. Time-resolved spectra obtained for a shot where driver beams were used. (a) Time-integrated spectrum, obtained by vertical binning of the streaked spectrum shown in (b). (c) Time profile of the various spectral components observed in the spectrum. (d) Time profile of the driver and interaction beam. The horizontal white and vertical black dotted lines, in (b) and (c) respectively, indicate the times of driver and interaction beam peaks.

Fig. 5. Comparison of SRS spectra obtained in shots with a variable number of interaction beams. No driver beams were used in these shots. The time-integrated spectrometer was located behind port . (a) Shots with (black line) and without (red line) the beam . (b) Shots with all the beams (blue lines) compared with shots where beams and (green lines) and , and (magenta lines) were switched off.

Fig. 6. (a) SRS and /2 intensities normalized by the number of beams versus the total laser energy. Measurements here refer to shots without the driver beams. Labels 6, 7 and 9 indicate the number of laser beams switched on in the shots. (b) Growth of /2 intensity versus the parameter .

Fig. 7. (a) Typical HE spectrum obtained by the EMSs, where the red rectangle shows the fitting region and the black dashed line is the background level. (b) Values of HE temperature obtained by the EMSs at 50° (black squares) and at 30° (red circles) and by the HEXS (blue triangles) versus the parameter. Solid and empty symbols indicate the shots without and with the driver beams, respectively. The relative uncertainty is 20 for all datasets, indicated as an example by the error bar on the left. The dashed lines represent the linear fitting for the complete sets of EMSs at 30°, EMSs at 50° and HEXS data.

Fig. 8. (a) Signal obtained in different IP in the HEXS and calculated deposited energy calculated by GEANT4 simulations using an exponential function with photon temperature of 24.5 keV. (b) The intensity measured by using targets with different plastic thickness and calculated values by using , keV.

Fig. 9. Curves of the growth of SRS reflectivity obtained from a multispeckle model (black) and a non-smoothed beam (red) as a function of the Rosenbluth gain calculated for the nominal laser intensity. Magenta and blue stars represent experimental results in shots without and with the driver beams, respectively, where the gain has been calculated considering the single-beam intensity. Empty stars represent shots with a smaller number of beams, as indicated by numbers 6, 7 and 9. The relative uncertainty of the reflectivity values due to the calibration procedure is around 30, which is as large as the star size.