Today's performance requirements for future DEMO gyrotrons are an operating frequency between 170 GHz up to 240 GHz and an output power of significantly larger than 1 MW (today's target: 2 MW). A total gyrotron efficiency of better than 60 % must be achieved. Multi-purpose/multi-frequency operation and frequency step-tunability are required also. It has been shown earlier, that the coaxial-cavity technology is a promising candidate [1]. In [2] a world record RF output power of 2.2 MW has been reported for short-pulses (in the range of few milliseconds). Nevertheless, it has to be proven that the coaxial-cavity technology can be used for long-pulse operation. That shall be achieved by upgrading the existing 2 MW 170 GHz short-pulse prototype used for the demonstration of the 2.2 MW record power. Additionally, a new Inverse Magnetron Injection Gun (IMIG) shall allow a significant larger emitter radius and therefore increased output power at operating frequencies significantly above 200 GHz by keeping the same or even smaller diameter of the warm bore hole of the superconducting gyrotron magnet. Both, the IMIG as well as the longer pulse gyro-tron will show the way towards higher output power at higher operating frequencies of gyrotrons together with a more robust design and construction of that kind of tubes.

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