## 3 ELIMAIA Dosimetry Description
### Detectors for Relative and Absolute Dosimetry
#### 3.2.3 Faraday Cup
If coupled with professional scanners for the optical density measurements, a measurement of dose distribution with a spatial resolution within about 200 um can be achieved after a proper calibration. This is important to precisely measure the X and Y beam profiles, necessary to retrieve the beam effective area of the primary beam impinging on the FC. Moreover, if assembled in a stack configuration, RCFs can provide a measurement of the energy spectrum through an iterative procedure that, starting from the last irradiated film in proximity of the beam range, takes into account the different contributions in the the previous films and, in turn, the correspondant relative weight for the final energy spectrum [44; 45]. Furthermore, EBT3 RCFs will be also used to measure the longitudinal dose distributions, assembling a single film in a dedicated PMMA phantom, divided in two identical parts, so that the film lies in a plane parallel to the beam direction (Figure 11). This approach, which can be further improved introducing post-processing corrections for high LET (Linear Energy Transfer) under-response, allows a precise measurement of the longitudinal dose distributions, and is particularly useful for quick determination of the beam range [45]. The ELIMAIA FC has been tested at high power laser facilities with the high energy laser-driven ion beams generated by the PW Vulcan laser system at the Rutherford Appleton Laboratory (UK). Such a preliminary characterization of the FC response in a laser environment has been performed during the experiment aimed at test the diamond-based ELIMAIA TOF diagnostics using the laser-target parameters described in Section 2.2. Figure 12 shows a picture of the FC connected to the target chamber through a pipe in backward direction at about 3 m from the target (Figure 12b). No kapton window was used to separate the FC from the target chamber during the test. A 25 um Cu foil was used in front of the FC aperture to stop the low energy proton group. The main goals were to investigate the charge response of the FC to highly pulsed ion beams and the effect of the intense EMP generated in the laser-target interaction, on the FC signal. Figure 12a shows time signal acquired by the FC generated by the different accelerated ion species and charge states. Figure 11: (**a**) PMMA phantom used to fix the radiochromic film (RCF) for longitudinal dose distributions; (**b**) An example of RFC irradiated with conventionally accelerated 62 MeV proton beams using the mentioned phantom, where it is clearly visible the increasing of darkness (and consequently, of dose) in proximity of the beam range. Particular care was taken to electrically isolate the FC from the chamber; different low pass-band filters were also used in the readout aiming to filter the EMP contribution from the ion current signal. As one can see, a positive current signal, resulting from the charge collected by the FC and corresponding in time to a signal generated by protons, carbon and oxygen ions (according to TPS data analysis, see Section 2.2), can be observed. In this case, because of the experimental configuration of the FC, the discrimination between proton and ion contributions was not possible. Nevertheless, these preliminary tests allowed to characterize the charge response, optimize the signal to EMP noise ratio, and emphasize the charged particle signal with respect to the EMP.