## 3 Elements of the Beam Line Prototype
### On-line Beam Diagnostics and Dosimetry
The charge collection response observed in the FC prototype is in agreement with the typical behavior of standard FCs used for absolute  
Figure 11: Charge collected by the FC prototype as a function of the bias applied to the external electrode. Figure 10: Transversal, longitudinal and radial components of the FC prototype electric field as a function of the FC longitudinal size, obtained using the COMSOL software (COMSOL, Brescia, Italy). dosimetry [22, 28]. The analysis of the charge measurement data using the internal beveled electrode is still on going. Nevertheless, based on a preliminary comparison the electric field resulting from the two coaxial electrodes improves the electron suppression efficiency. Recently, characterizations of the electromagnetic pulse (EMP) effect on the FC prototype signal has been carried out at the PALS laser facility, in Prague (Czech Republic) and at the TARANIS laser facility at the Queen's University in Belfast (UK). Typically, a high power laser-matter interaction and the subsequent plasma production are accompanied by the emission of an intense EMP, which propagates inside and outside the interaction chamber [32] interfering with the diagnostic devices and affecting their response. Therefore, particularly for a dosimeter, it is crucial to perform a systematic study, in terms of frequencies and amplitude of the EMP generated by the laser pulse, to perform accurate dose evaluations. Indeed, the EMP produces a not-negligible background signal that, if not carefully characterized, does not allow a precise charge measurement [32]. The FC prototype has been tested by using a laser-driven proton beam during an experiment [27] performed at the PALS laboratory (Prague, Czech Republic), where a 2 TW laser system (about 1 KJ of energy delivered on target and a time duration of 300 ps) is available. The FC was mounted inside the experimental hall at approximately 2 and 5 m from the interaction chamber for a characterization of the EMP propagating outside of the chamber and directly connected to the interaction chamber at 30\({}^{\circ}\) in the backward direction with respect to the target normal axis. The FC signal was registered with a 2 GHz Le Croy Digital Oscilloscope. Figure 12 shows a typical FC signal registered during the experiment. As one can see from the inset in Figure 12, the EMP is characterized by frequency components from few hundreds of MHz up to 2 GHz. Based on the frequency analysis, the significant noise signal results from the EMP propagation inside the interaction chamber [33, 34] and seems to be predominant with respect to the charge signal, affecting the measurement of the total collected charge. Nevertheless, the cumulative integration of the FC signal, as shown in Figure 13, reveals the presence of a charge contribution that, although very small, can be separated by the huge EMP noise contribution [27]. Indeed, even though the EMP signal is present, a null final cumulative value is expected due to their identical positive and negative contributions to the integral. On the other hand, for those signals registered when the FC is mounted on the interaction chamber (_i.e._ along the plasma emission direction) a signal generated by the incoming charged particles accelerated from the target is expected to be present  
Figure 12: A FC signal registered during the PALS experiment. The inset shows the Fast Fourier transformation of the signal. together with the typical EMP contribution. Therefore, as it can be observed in Figure 13, the cumulative of those signals deviates from a null final integral showing a decreasing-negative trend, which indicates a continuous negative contribution to the integrated signal. This result indicates the necessity to perform a thorough study to allow the separation of the noise contribution from the physical signal. The use of appropriate electronic circuits, as filter amplifiers, and also proper EMP shielding will allow removing or reducing the higher frequency contributions related to the EMP.