Tests of a cooling system for thin targets submitted to intense ion beams for the numen experiment

The NUMEN experiment, hosted at LNS (Catania, Italy), aims to determine the Nuclear Matrix Elements (NMEs) involved in 0β β decay via heavy-ion induced Double Charge Exchange (DCE) reactions. High intensity beams of about 50 μA and of energies ranging from 15 to 60 MeV/u are necessary, due to the low DCE cross sections and the use of very thin targets (several hundreds of nm) needed to reach the required energy resolution. These intense beams produce a considerable amount of heat inside the target, which can be dissipated by depositing the targets on a highly thermally conductive substrate, HOPG (Highly Oriented Pyrolytic Graphite), and coupling it with a suitable designed target-cooler system. The heat transfer from the beam spot to the cold region has been studied by solving numerically the heat equation to determine the evolution in space and time of the temperature inside the target. According to calculations, the temperatures of most of the target isotopes remain under the melting points. Experimental tests with a laser were initiated to validate the whole cooling system and the calculations.