A 5 W, 700 GHz Gyrotron for Scattering Diagnostics in Burning Plasmas

As the fusion science research advances towards the demonstration of practical reactors for commercial adoption there is a growing need to develop diagnostic systems for monitoring various plasma parameters in real time for control and shaping of the plasma density and profile. Recent, experiments have demonstrated the potential of a High-k Scattering system for studying turbulence physics studies by providing a measurement of the kθ-spectrum of both electron temperature gradient (ETG) and ion temperature gradient (ITG) modes. Currently, a large and bulky Far Infrared (FIR) laser system in use at the National Spherical Torus Experiment - Upgrade (NSTX-U) for such experiments. The output power of the laser is only 50 mW at 693 GHz. The availability of a 5 W source which is more compact, robust and efficient will enable further development of this technique for eventual deployment in future reactors such as DEMO. We propose to develop a compact second harmonic gyrotron that can generate > 5 W of continuous wave power at 693 GHz. The gyrotron technology can be easily extended to any frequency in the 1 THz range using currently available magnet technology and hence have wide applicability in different fusion reactors operating over a range of plasma density and magnetic field. The development of such a source will be essential for real time plasma monitoring in a commercial reactor. In the short term, such receivers will advance further development of this technique and methods at experiments such as the National Spherical Torus Experiment - Upgrade (NSTX-U).