[IEEE 2011 36th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2011) - Houston, TX, USA (2011.10.2-2011.10.7)] 2011 International Conference on Infrared, Millimeter, and Terahertz Waves - Tunable second harmonic gyrotron based on a 12 T superconducting, cryogen-free magnet