## EOS Detector
### Scintillator Screen Diagnostics
#### 3.2.3 Laser-Solid Target Interaction Experimental Campaign  
Ion acceleration from high-intensity laser-target interaction can generate large amounts of particles with MeV energies [53; 54; 55]. According to models [56; 57; 58], the process begins with electrons being accelerated by the laser at the front of the target where a plasma is generated and, in turn, directed towards the target (normally a thin foil). Some of these electrons, the fastest, more energetic component, can reach the rear of the target [59]. When escaping the target, they induce a huge electrostatic field close to the surface due to the unbalanced positive charge [60] left on it and the runaway electron locked nearby. The generated electric field can accelerate rear surface ions in a process called Target Normal Sheath Acceleration (TNSA) [57]. Figure 21: Betatron radiation spectrum with the optimized FLAME laser system. Figure 22: Shadowgraph of an iron slab (**left**) close to a tilted Allen key (**right**). At FLAME [15; 23], we have performed temporally resolved measurements of the fast electrons component escaping the target and of the electromagnetic pulses produced during the laser-target interaction. We exploited Electro-Optical Sampling (see Figure 10) [18] diagnostics, which are widely adopted in conventional accelerators [19; 61; 62], presenting sub-picosecond resolution. Moreover, we investigated the contribution of the target properties, such as shape [19] and material [60], in the fast electron emission. Several extensive experimental campaigns [19; 20; 22] have been carried out with the FLAME laser system adopting the setup in Figure 10.  
In the following, we provide information on three experiments performed at SPARC_LAB: one devoted to fast electron characterization, one to EMPs detection, and the last one regarding electron-proton beam correlation. Fast Electron Beams Detection  
Adopting the designed setup shown in Figure 10, we successfully detected the fast electron beams [63; 64], which were accelerated during the interaction process between the FLAME main laser beamline and a solid target. In our experimental setup, since the distance between the EOS crystal and the target is significantly greater than the Debye length of approximately 1 \(\upmu\)m, only the highly energetic electrons overcoming the potential barrier can reach our diagnostics. The high-resolution EOS diagnostic method enables us to work within the same temporal scale as the process, which is defined by the duration of the main laser pulse [60; 65]. Earlier research on laser-driven ion acceleration has indicated a notable rise in the energy of accelerated ions when structured targets [66; 67; 68] were utilized, in contrast to the traditional thin aluminum foils used in the TNSA scheme. To achieve this goal, we experimented with various target geometries: a 10 \(\upmu\)m thick aluminum foil and the tip of a needle. By measuring the charge amount and energy of the escaping electrons using the EOS detector, as previously described, we obtained the necessary evidence for the field-enhancement hypothesis, as summarized in Figure 23.  
A clear indication of increased charge and energy with sharp tips can be inferred by the presence of a second ultra-short electron bunch in the nC range. Electromagnetic Pulses Detection  
The interaction of an ultra-intense laser with a solid target generates a significant amount of EMPs. In addition to the capability of detecting fast electrons, our EOS diagnostics have enabled us to uncover these EMPs. Figure 24 displays the temporal evolution of the EMPs emitted during the interaction process. The retrieved trace was recorded by incrementally delaying the probe laser arrival  
Figure 23: Fast electrons bunches for different target shapes (1) planar and (2) tip targets. The emitted charges are, respectively, (1) 1.2 nC (Bunch 1—B1) and 3 nC (Bunch 2—B2) and (2) 7 nC (Bunch 1—B1) and 3 nC (Bunch 2—B2). Adapted from Ref. [19].