Jawla, Sudheer K., Robert G. Griffin, Ivan A. Mastovsky, Michael A. Shapiro, and Richard J. Temkin. “Second Harmonic 527-GHz Gyrotron for DNP-NMR: Design and Experimental Results.” IEEE Transactions on Electron Devices 67, no. 1 (January 2020): 328–34.
We report the design and experimental demonstration of a frequency tunable terahertz gyrotron at 527 GHz built for an 800-MHz dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP-NMR) spectrometer. The gyrotron is designed at the second harmonic (ω = 2ωc) of the electron cyclotron frequency. It produces up to 9.3-W continuous microwave (CW) power at 527.2-GHz frequency using a diode type electron gun operating at V = 16.65 kV, Ib = 110 mA in a TE11,2,1 mode, corresponding to an efﬁciency of ∼0.5%. The gyrotron is tunable within ∼0.4 GHz by combining voltage and magnetic ﬁeld tuning. The gyrotron has an internal mode converter that produces a Gaussian-like beam that couples to the HE11 mode of an internal 12-mm i.d. corrugated waveguide periscope assembly leading up to the output window. An external corrugated waveguide transmission line system is built including a corrugated taper from 12- to 16-mm i.d. waveguide followed by 3 m of the 16-mm i.d. waveguide The microwave beam proﬁle is measured using a pyroelectric camera showing ∼84% HE11 mode content.