Development of GEM-based beam monitor operated in $N_{2}$ for ESS-Freia.

The work is related to the design and development of a gas-based beam monitor for cold neutrons for ESS. The innovative element of this monitor lies in the use of a gas mixture (Ar-$N_{2}$) both as a conversion agent and as an ionizable gas, exploiting in particular a nuclear reaction in nitrogen for neutron conversion. For applications in ESS, the monitor has to be small in size with low impact on the beam, $i.e.$, no more than $2%$ of the neutron beam can be removed by the monitor. Simulations are carried on with the Geant4 software to discriminate which material has less impact on the beam and to evaluate the dimensions of each layer to optimize the interaction efficiency between gas and neutrons. Experimental results are shown in this work about the characterization of the monitor prototype with the use of X radiation at the ISTP institute and at Milano-Bicocca University to study its physical and electronical functionality. Preliminary results with thermal and cold neutrons were also obtained using the neutron source at LENA.