Gyrotron, classified as free electron MASER (Microwave Amplification by Stimulated Emission of Radiation), is a high power high frequency oscillator used in the external heating of fusion plasma. The large amount of heat released in the resonant cavity represent the main limitation of the Gyrotron. Hence, a more efficient cooling is necessary and mini-channels cooling system have already been individuated as a possible solution to be investigated. A mock-up with an entire circular cavity has been realized and hydraulic test have been performed in order to compare the result of the hydraulic simulation. In the mock-up realization a new additive technology, patent by Thales, has been used to test the possibility of use it in the realization of future gyrotrons.