Modular, triple–resonance, transmission line DNP MAS probe for 500 MHz/330 GHz's picture
TitleModular, triple–resonance, transmission line DNP MAS probe for 500 MHz/330 GHz
Publication TypeJournal Article
Year of Publication2019
AuthorsReese, M, George, C, Yang, C, Jawala, S, J. Grün, T, Schwalbe, H, Redfield, C, Temkin, RJ, Griffin, RG
ISBN Number1090-7807
Keywordsbalanced transmission line probe, NMR probe characterization, novel probe design, Solid state DNP

We describe the design and construction of a modular, triple–resonance, fully balanced, DNP-MAS probe based on transmission line technology and its integration into a 500MHz/330GHz DNP-NMR spectrometer. A novel quantitative probe design and characterization strategy is developed and employed to achieve optimal sensitivity, RF homogeneity and excellent isolation between channels. The resulting three channel HCN probe has a modular design with each individual, swappable module being equipped with connectorized, transmission line ports. This strategy permits attachment of a mating connector that facilitates accurate impedance measurements at these ports and allows characterization and adjustment (e.g. for balancing or tuning/matching) of each component individually. The RF performance of the probe is excellent; for example, the 13C channel attains a Rabi frequency of 280 kHz for a 3.2mm rotor. In addition, a frequency tunable 330 GHz gyrotron operating at the second harmonic of the electron cyclotron frequency was developed for DNP applications. Careful alignment of the corrugated waveguide led to minimal loss of the microwave power, and an enhancement factor ε=180 was achieved for U-13C urea in the glassy matrix at 80K. We demonstrated the operation of the system with acquisition of multidimensional spectra of cross-linked lysozyme crystals which are insoluble in glycerol-water mixtures used for DNP and samples of RNA.

Short TitleJournal of Magnetic Resonance