Design considerations for future DEMO gyrotrons: A review on related gyrotron activities within EUROfusion

•The research work on multi-megawatt fusion gyrotrons with an operating frequency significantly above 200GHz together with an RF output power of more than 1MW and a total gyrotron efficiency of better than 60% is summarized. It includes research on frequency tunable gyrotrons and multi-purpose gyrotrons.•Principle feasibility of coaxial-cavity gyrotron technology is compared to conventional hollow-cavity technology. Both options are studied with regards to maximum achievable output power versus efficiency, operation stability and tolerances.•Research for multi-stage depressed collectors (MSDC) is summarized.