## 1 Introduction  
The SORGENTINA-RF project aims to develop a 14 MeV neutron source from deuterium-tritium fusion reactions with an expected power of 250 kW with the main purpose of producing medical radioisotopes as highlighted by some recent experimental evidence obtained at ENEA laboratories [1, 2]. The neutron source is based on an ion source and accelerator which, from a gas of deuterium (D2) and tritium (T2), produce, extract, and accelerate D+ and T+ ions up to 300 keV against a rotating target fusion reactions occur thus producing 14 MeV neutrons. In particular, the 14 MeV neutron source will be used to assess the production of 99 Mo as a precursor of 99 mTc, widely used in medical diagnostics for SPECT (Single-Photon-Emission Computed Tomography). The project represents a step towards a plant where relevant quantities of molybdenum can be irradiated and in turn radiochemical treatment at the same site. For its complexity, the project is divided into two main steps: in the first phase, the so-called thermo-mechanical demonstrator, composed of a rotating target equipped with the heat removal system and the ion source will be developed and tested separately; in the second, the ion source and the radiochemical facility for molybdenum treatment will be fully developed. More in detail, the assembly depicted in Figure 1 is composed of the rotating target and its auxiliary components (i.e., vacuum chamber, reservoir, etc.). The rotating target has a double scope, allowing the implantation of deuterium and tritium into a thin titanium layer (about 3 \(\upmu\)m) properly deposited on the target surface and dissipating the thermal power (250 kW) delivered by the accelerator. The heat source for the rotating target consists of an ion source (currently in a design stage) accelerating both deuterium and tritium against the external cylindrical surface of the rotating target. The colliding particles are collimated in a circular shape (150 mm in diameter) by the accelerating grids while the ion source is inclined by 45\({}^{\circ}\) on the vertical plane. This layout generates an elliptical footprint on the external surface of the rotating target. Regarding the homogeneity of the heat generated, the ion source will grant a \(\pm\)10% difference all over the impact surface that is simulated with a uniform heat flux boundary condition in the FEM analyses. The rotating target is a prototypical out-of-scale rotating heat pipe (RHP) (Patent PCT/IB2019/051,972). The RHP mainly consists of three regions: the evaporator where a fluid is heated up (by the ion source) to its evaporation/boiling (in the upper region), a lower conical condenser region where the vapour previously generated finds a cold surface to condensate and then moves back to the evaporator thanks to the centrifugal effect of the rotation, an adiabatic region between the two previous ones where the condensate moves back to the evaporator. The general description of the project and the main activities can be found in further detail in [3] while a set of specific studies is presented in [4; 5; 6; 7; 8; 9; 10]. In this paper, the methodology and main outcomes from the analysis for the design and optimisation of the prototype of the rotating target are discussed. The rotating target can be essentially divided into three regions: the upper part, henceforth named the evaporator, the lower part, named the condenser connected to the external cooling system for heat removal, and the mid-region in between the two. The Finite Element Method (FEM) was adopted to calculate the strength of the rotating target under complex load scenarios as the one foreseen during the functioning of the device. Several thermo-mechanical analyses were performed in order to investigate the mechanical performance of the target and the main numerical results are herein discussed. The temperature field, resulting from the energy deposition of D+ and T+ ions into the target and removed by the cooling system, has been evaluated in previous studies [6] and here used as input in FEM analyses.