A 250 GHz gyrotron for NMR spectroscopy

Summary form only given. A gyrotron-based spectrometer suitable for nuclear magnetic resonance (NMR) studies at 380 MHz has been constructed. This spectrometer is being used to study dynamic nuclear polarization (DNP), a technique that can result in significant enhancement of the NMR signal. Signal enhancements up to forty have been measured in the /sup 13/C spectra of glycerol/water/TEMPO. An important component of this system is a compact 250 GHz fundamental gyrotron oscillator operating in the TE/sub 031/ mode. This source typically operates at a beam voltage of 12-16 kV, and at currents up to 50 mA. A 9.4 T magnet with a 6.4 cm diameter vertical bore produces the magnetic field. The gyrotron occupies the vertical bore, while a radial bore is used for the transmission of the microwave power through a side vacuum window of the tube. As a result, the electron beam and microwave power can be separated just after the interaction in the gyrotron cavity. This reduces ohmic losses in the output waveguide, and simplifies the design of the beam collector. An internal quasi-optical mode converter is used to convert the TE/sub 031/ cavity mode into a Gaussian output beam.