Instrumentation for cryogenic magic angle spinning dynamic nuclear polarization using 90L of liquid nitrogen per day

[Display omitted] •Counterflow heat exchanger design reduces nitrogen consumption to 90L/day.•Computational fluid dynamics analysis describes heat exchanger performance.•80K sample temperature yields DNP enhancement of 328.•Robust design and low H2O content permits extended continuous operation (>...

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Bibliographic Details
Published in:Journal of magnetic resonance (1997) 2017-10, Vol.283, p.71-78
Main Authors: Albert, Brice J., Pahng, Seong Ho, Alaniva, Nicholas, Sesti, Erika L., Rand, Peter W., Saliba, Edward P., Scott, Faith J., Choi, Eric J., Barnes, Alexander B.
Format: Article
Language:English
Subjects:
Cold Temperature
Cryogenic MAS
Dynamic nuclear polarization
Electron decoupling
Gases
Heat exchanger
Magic-angle spinning
Magnetic Resonance Spectroscopy - instrumentation
Magnetic Resonance Spectroscopy - methods
Microwaves
Nitrogen - chemistry
Pulsed DNP
Solid-state NMR
Temperature
Urea - chemistry
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Summary:[Display omitted] •Counterflow heat exchanger design reduces nitrogen consumption to 90L/day.•Computational fluid dynamics analysis describes heat exchanger performance.•80K sample temperature yields DNP enhancement of 328.•Robust design and low H2O content permits extended continuous operation (>5weeks). Cryogenic sample temperatures can enhance NMR sensitivity by extending spin relaxation times to improve dynamic nuclear polarization (DNP) and by increasing Boltzmann spin polarization. We have developed an efficient heat exchanger with a liquid nitrogen consumption rate of only 90L per day to perform magic-angle spinning (MAS) DNP experiments below 85K. In this heat exchanger implementation, cold exhaust gas from the NMR probe is returned to the outer portion of a counterflow coil within an intermediate cooling stage to improve cooling efficiency of the spinning and variable temperature gases. The heat exchange within the counterflow coil is calculated with computational fluid dynamics to optimize the heat transfer. Experimental results using the novel counterflow heat exchanger demonstrate MAS DNP signal enhancements of 328±3 at 81±2K, and 276±4 at 105±2K.
ISSN:1090-7807
1096-0856
DOI:10.1016/j.jmr.2017.08.014