A 250 GHz gyrotron with a 3 GHz tuning bandwidth for dynamic nuclear polarization
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Griffin_A 250ghz gyrotron.pdf
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Author(s)
Barnes, Alexander B.
Nanni, Emilio Alessandro
Herzfeld, Judith
Temkin, Richard J.
Griffin, Robert Guy
Date Issued
March 2012
Journal
Journal of Magnetic Resonance
Publisher
Elsevier
Citation
Barnes, Alexander B., Emilio A. Nanni, Judith Herzfeld, Robert G. Griffin, and Richard J. Temkin. “A 250GHz Gyrotron with a 3GHz Tuning Bandwidth for Dynamic Nuclear Polarization.” Journal of Magnetic Resonance 221 (August 2012): 147–153.
Version
Author's final manuscript
Abstract
We describe the design and implementation of a novel tunable 250 GHz gyrotron oscillator with >10 W output power over most of a 3 GHz band and >35 W peak power. The tuning bandwidth and power are sufficient to generate a >1 MHz nutation frequency across the entire nitroxide EPR lineshape for cross effect DNP, as well as to excite solid effect transitions utilizing other radicals, without the need for sweeping the NMR magnetic field. Substantially improved tunability is achieved by implementing a long (23 mm) interaction cavity that can excite higher order axial modes by changing either the magnetic field of the gyrotron or the cathode potential. This interaction cavity excites the rotating TE[subscript 5,2,q] mode, and an internal mode converter outputs a high-quality microwave beam with >94% Gaussian content. The gyrotron was integrated into a DNP spectrometer, resulting in a measured DNP enhancement of 54 on the membrane protein bacteriorhodopsin.
MIT Department
Massachusetts Institute of Technology. Department of Chemistry
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Plasma Science and Fusion Center
Francis Bitter Magnet Laboratory (Massachusetts Institute of Technology)
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DOI of Published Version
https://doi.org/10.1016/j.jmr.2012.03.014
