Demonstration of a 263 GHz gyrotron for Dynamic Nuclear Polarization

Summary form only given: Dynamic nuclear polarization (DNP) can be used to increase the sensitivity of nuclear magnetic resonance (NMR) experiments by transferring the much higher polarization of unpaired electrons spins to nuclear spins. The polarization transfer is driven by high frequency millimeter wave irradiation. Communications and power industries is an original equipment manufacturer of gyrotron tubes for Bruker Biospin's 263 GHz DNP spectrometer, which is used with a 400 MHz NMR system. The key components of the DNP system include a cw gyrotron tube operating near 263 GHz at power levels of 25 W, nominally , a 9.7 T superconducting magnet, a power supply and control system, a transmission line from the gyrotron to the NMR sample, and a low- temperature magnetic-angle-spinning probe. The recently developed 263 GHz gyrotron, which has experimentally demonstrated over 70 W cw output power, operates in the TE
_0.3
mode. The single-anode magnetron injection gun operates nominally at 15 kV and 30 mA and produces a high-quality electron beam in the cavity. The 9.7 T magnetic field is generated by a Bruker superconducting magnet. The TE
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mode is transformed to a Gaussian-like beam via an internal mode converter with a simple step-cut Vlasov launcher and five mirrors to steer and shape the RF beam. Experimental results, which include power tuning curves, frequency tuning curves, and infrared images of the output beam, will be detailed.