Design of a 460 GHz Continuous-Wave Gyrotron Operating at TE11,2 Mode

Dynamic nuclear polarization enhanced nuclear magnetic resonance (DNP/NMR) requires a high power continuous-wave (CW) electromagnetic wave source in the submillimeter wavelength range to obtain significant enhancements in spin spectra from biological samples. Having the ability to generate very high power at submillimeter wavelengths, gyrotrons are well suited for use in DNP/NMR spectrometers1. A 460 GHz CW gyrotron for DNP enhanced 700 MHz NMR spectroscopy has been developed", and day-long stable operation has been demonstrated1 at MIT. In this presentation, an upgraded design of the 460 GHz gyrotron will be discussed. To produce higher and more stable output with the present 12 kV electron gun, TE_11.2 mode is selected. This design is capable of lowering the starting oscillation current to 26 mA with the 30 mm long cavity. From simulations using a nonlinear gyrotron code, MAGY, above 60 watts of output power is predicted with the beam current of 100 mA. A Vlasov-tvpe launcher with a helical cut is designed for the coupling of the whispering-gallery mode. High power radiation with good spectral and spatial characteristics from this tube should provide NMR spectrometers with high signal enhancement. Besides experimental progress to implement the DNP/NMR spectrometer, other possible applications to utilize this powerful CW submillimeter-wave source, will also be discussed.