Category Archives: Probe Design

Modular, triple-resonance, transmission line DNP MAS probe for 500 MHz/330 GHz #DNPNMR

Reese, Marcel, Christy George, Chen Yang, Sudheer Jawla, J. Tassilo Grün, Harald Schwalbe, Christina Redfield, Richard J. Temkin, and Robert G. Griffin. “Modular, Triple-Resonance, Transmission Line DNP MAS Probe for 500 MHz/330 GHz.” Journal of Magnetic Resonance 307 (October 2019): 106573.

https://doi.org/10.1016/j.jmr.2019.106573.

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 3.2 mm 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 =180 was achieved for U-13C urea in the glassy matrix at 80 K. 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.

Tunable 13C/1H dual channel matching circuit for dynamic nuclear polarization system with cross-polarization #DNPNMR

Rybalko, Oleksandr, Sean Bowen, Vitaliy Zhurbenko, and Jan Henrik Ardenkjar-Larsen. “Tunable 13C/1H Dual Channel Matching Circuit for Dynamic Nuclear Polarization System with Cross-Polarization.” In 2016 46th European Microwave Conference (EuMC), 1227–30. London, United Kingdom: IEEE, 2016.

https://doi.org/10.1109/EuMC.2016.7824571

In this paper we report initial results of design and practical implementation of tuning and matching circuit to estimate a performance of Dynamic Nuclear Polarization (DNP) at a magnetic field of 6.7 T. It is shown that developed circuit for signal observation is compact, easy to make and provides low return loss (typically better than – 45 dB) at a tuning range ±3 MHz for both resonant frequencies. In addition, transmission parameters measured between 13C and 1H channels are less than – 17 dB and – 50 dB for 71.8 MHz and 285.5 MHz, respectively showing a good isolation between the two channels. Measurement results with a tuning and matching circuit prototype are presented including obtained spectra (13C and 1H) and estimation of the signal-to-noise ratio.

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