400 MHz/263 GHz ultra-low temperature MAS-DNP using a closed-cycle helium gas cooling system and a solid-state...

Area of Science:

• Solid-state Nuclear Magnetic Resonance (NMR) Spectroscopy
• Dynamic Nuclear Polarization (DNP)
• Low-Temperature Physics

Background:

• Magic-angle spinning (MAS) dynamic nuclear polarization (DNP) is crucial for solid-state NMR.
• Conventional MAS-DNP systems use gyrotrons and operate at ~100 K with nitrogen gas.
• These conventional systems face limitations in terms of size, cost, and frequency agility.

Purpose of the Study:

• To introduce a novel 400 MHz/263 GHz MAS-DNP system.
• To demonstrate the advantages of using a compact solid-state microwave source and an ultra-low temperature (ULT) helium MAS probe with a cryogenic preamplifier.
• To evaluate the system's performance and sensitivity gains compared to conventional methods.

Main Methods:

• Development of a MAS-DNP system integrating a solid-state microwave source and a ULT helium MAS probe.
• Inclusion of a cryogenic preamplifier to boost signal-to-noise ratio.
• Testing the system with a standard proline sample at 30 K and 160 mW microwave power.

Main Results:

• Achieved a DNP enhancement factor of 85 for proline at 30 K.
• Observed an 11x additional sensitivity gain at 30 K due to Boltzmann polarization and the cryogenic preamplifier compared to 100 K.
• Estimated overall sensitivity gain of approximately double that of a 100 K gyrotron system.

Conclusions:

• The ULT-DNP system offers a significant sensitivity enhancement, making it a viable and advantageous alternative to conventional gyrotron-based systems.
• Solid-state microwave sources provide compactness, cost-effectiveness, and frequency agility.
• The combination of ULT and cryogenic preamplification effectively compensates for lower microwave power and improves overall performance.