In nuclear fusion machines, plasma heating is provided by the Electron Cyclotron Heating System where gyrotrons are typically employed to produce radiofrequency waves to be injected into the plasma chamber. The gyrotrons for the next generation of tokamaks and stellarators target a delivered power of 2 MW in continuous mode operation. While the hollow-cavity gyrotron concept requires significant R&D improvements in the thermal management of the cavity to minimize thermal deformation and frequency shift, the coaxial-cavity gyrotron concept facilitates improved mode competition control, eventually increasing the output power per tube while keeping the heat load on the cavity wall at an acceptable level.