NMR Probe Counterflow Heat Exchangers for Ultra-Low Temperature MAS-DNP
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Solution Overview
Problem
Existing NMR probes struggle with low sensitivity and are not compatible with ultra-low temperature (ULT) operations below 80 K, especially when performing Magic Angle Spinning (MAS) and Dynamic Nuclear Polarization (DNP) techniques.
Innovation Solution
The integration of multiple compact high-effectiveness counterflow heat exchangers within the NMR probe allows for efficient cooling and operation at ultra-low temperatures, enabling MAS DNP capabilities while being compatible with standard helium recycling systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional NMR probes are used, then ease of operation is maintained, but sensitivity is insufficient and ultra-low temperature operation is not achieved
Solution Approach 1:
The probe is divided into functionally independent modules: a cryogenic cooling system with counterflow heat exchangers for temperature control, a MAS spinning system for sample rotation, and a DNP microwave irradiation system for nuclear polarization. Each module operates independently while contributing to the overall sensitivity enhancement, allowing the probe to achieve ULT operation without requiring complete redesign of conventional probe architecture.
Solution Approach 2:
The probe integrates multiple functions into a single device: cryogenic cooling to ultra-low temperatures, Magic Angle Spinning for high-resolution NMR, and Dynamic Nuclear Polarization for sensitivity enhancement. This multi-functional design eliminates the need for separate systems and achieves both improved sensitivity and operational versatility without proportionally increasing complexity.
2Measurement precision
If purpose-built static NMR probes are designed for ULT operation, then sensitivity is improved, but device complexity and cost increase significantly
Solution Approach 1:
The invention merges the MAS spinning capability with ULT cryogenic cooling and DNP functions into a single integrated probe system. By combining these functions that were previously implemented in separate devices or systems, the probe achieves enhanced sensitivity and operational versatility without requiring multiple independent purpose-built probes, thereby reducing overall device complexity and cost.
Solution Approach 2:
The probe utilizes counterflow heat exchangers to efficiently transfer heat at ultra-low temperatures, enabling the system to operate down to 4.2 K. By optimizing thermal parameters and using phase-change materials, the probe achieves stable ULT operation without requiring complex cryogenic systems, thus improving sensitivity while controlling device complexity through parameter optimization rather than structural complexity.
3Loss of substance
If helium recycling systems are used, then operating costs are reduced, but helium consumption increases
Solution Approach 1:
The probe incorporates a helium recycling system that captures and recovers helium from the cryogenic cooling process and MAS spinning operations. By recovering helium that would otherwise be lost or vented, the system reduces net helium consumption while maintaining efficient cooling and spinning operations, thereby lowering operating costs without significantly increasing substance loss.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution dramatically reduces helium consumption and operating costs, enhances the breadth of functional capabilities, and allows for faster sample temperature changes, making ULT NMR-MAS-DNP accessible at a lower cost and with reduced laboratory space requirements.
Implementation Method 1
The integration of multiple compact high-effectiveness counterflow heat exchangers within the NMR probe allows for efficient cooling and operation at ultra-low temperatures
Implementation Method 2
NMR is the most powerful analytical technique for molecular structure determination
Implementation Method 3
rapid spinning of the sample at the 'Magic Angle' (the zero of the second Legendre polynomial, 54.7°) with respect to B0
Implementation Method 4
Dynamic Nuclear Polarization (DNP) techniques... enabling MAS DNP capabilities
Data Source
AI summary
An NMR probe for insertion into an NMR magnet from below is disclosed that includes multiple counterflow heat exchangers to enable a wide range of NMR methods at ultra low temperatures, including MAS DNP at temperatures below 15 K. Coolant fluid is ducted from the bottom of the probe through a vacuum insulated transfer line up into the probehead, the region containing the sample and sample coil, where it splits into first and second coolant streams for cooling first and second spin-gas streams, each through a cold counterflow exchanger and at least one cool counterflow exchanger contained within the probe.The cold exchangers would each preferably comprise two straight continuously joined tubes inside a dewared tube that extends from a vacuum chamber in the base of the probe up into the probehead. These cold exchangers are denoted as Dual Inner Tube Exchangers (DITEs). The cool exchanger is preferably a coil of two parallel continuously thermally joined tubes, and it is denoted as a Parallel Tube Recuperator (PTR).The first coolant-stream in the probehead feeds into the top of DITE-1, through which the first coolant stream flows downward, providing final cooling to the first spin gas stream which is flowing upward past it into the probehead. The first coolant stream leaving the bottom end of DITE-1 then enters the cooler end of a first PTR in an evacuated chamber in the base of the probe and proceeds through the first PTR to its warmer end in counter-current to the first spin gas stream which had entered at the warmer end of first PTR, exited at its cooler end, and proceeded into the bottom end of DITE-1. An additional PTR may be series connected to the first PTR to further improve the overall effectiveness of heat transfer from first spin gas stream to the first coolant stream.In like manner, the second coolant stream cools a second spin gas stream.The exchangers are designed to permit fast MAS at temperatures below 15 K when the probe is supplied with room-temperature helium spin gas streams at commonly used pressures and a helium coolant stream at less than 170 kPa from a standard portable helium cryostat. Liquid helium usage rate is typically in the 2-12 L/hr range, depending on the spinning rate and sample temperature. Both the spin gases and the coolant fluid are fully recoverable without contamination for recycling using the standard helium recycling methods and equipment (with minor upgrades) commonly found in many NMR laboratories.