## 4 Conclusions  
An YBCO film superconductor has been studied by means of AC susceptibility measurements as a function of the AC amplitude, temperature, and DC field. The first harmonic imaginary component of the AC susceptibility \(\chi_{1}^{{}^{\prime\prime}}\) related to the dissipation processes of the sample has been measured initially as a function of the AC amplitude at different AC frequencies, DC fields, and at 77 K in order to obtain the critical current density \(\rm J_{c}\) and, consequently, the pinning energy U values. From these curves, the presence of a double peak with increasing DC fields has been noted, indicating the presence of granularity inside the sample. In particular, the inter-grain link between the grains is responsible for the first peak at low DC fields, which quickly vanishes, while the contribution from individual grains is responsible for the second peak, which forms at higher DC fields. From the position of the peaks, the U values have been extracted and graphed as a function of the DC field, showing a crossover from a single vortex pinning regime to a collective one. After that, the temperature dependence of the \(\chi_{1}^{{}^{\prime\prime}}\) at different DC fields has been studied, revealing a double-peak structure correlated with the granularity of the sample. By taking the temperature corresponding to the minimum between the two peaks, a contour plot of the \(\chi_{1}^{{}^{\prime\prime}}\) with the temperature and DC field values has been drawn, allowing for separating the inter- and intragranular response of the sample. Finally, the temperature has been fixed to 77 K, in view of the possible applicability of the material for power applications, together with an AC frequency equal to 1597.9 Hz, and the \(\chi_{1}^{{}^{\prime\prime}}\) as a function of the DC field at different AC amplitudes has been analyzed. At this temperature, the granularity  
Figure 8: The contour plot of the \(\chi_{1}^{{}^{\prime\prime}}\) with the DC field and AC amplitudes is evidence of the intergranular and intragranular regions of the sample. At this temperature, 77 K, and at this AC frequency, the intragranular contribution is much more active than the intergranular one.  
is strongly present at all the AC amplitudes even if the intragranular response is wider than the intergranular one. This aspect can be important when the sample is studied by applying a magnetic field instead of probing the sample with transport measurements because the creation of the superconducting currents due to the applied field are favored to form inside the grains rather than among the grains' weak links. This aspect makes this material interesting for several types of applications, such as energy transmission, signal filtering, and magnetic confinement fusion.  
Conceptualization, A.G. and A.C.; methodology, A.G. and A.C.; software, A.G., A.M.I. and A.L.; validation, A.C. and I.I.; formal analysis, A.G. and A.C.; investigation, A.G.; resources, G.G. and M.P.; data curation, A.G., A.C. and A.M.I; writing--original draft preparation, A.G.; writing--review and editing, A.C., A.M.I, I.I. and A.L.; visualization, A.L., G.G. and M.P.; supervision, G.G. and M.P.; project administration, G.G. and M.P.; funding acquisition, A.C., G.G. and M.P. All authors have read and agreed to the published version of the manuscript.  
This work was supported by the EU COST Actions CA19108 Hi-SCALE, CA20116 OPERA, and CA21144 SUPERQUMAP. A.C. gratefully acknowledges the funding from the Core Program of the National Institute of Materials Physics, granted by the Romanian Ministry of Research, Innovation and Digitalization under the Project PC2-PN23080202. G.G. acknowledges partial financial support by the PRIN 2022 PNRR Project QUESTIONS Grant No. P2022 KWFBH.  
Not applicable.  
The data sets that support the findings in this study are available from the corresponding authors upon reasonable request.  
The authors declare no conflicts of interest.