Post-acquisition correction of NMR spectra distorted by dynamic and static field inhomogeneity of cryogen-free magnets.

Post-acquisition correction of NMR spectra is an important part of NMR spectroscopy that enables refined NMR spectra to be obtained, clean from undesirable out-phasing, broadening and noising. We describe analytical and numerical mathematical methods for post-acquisition correction of NMR spectra distorted by static and dynamic magnetic field inhomogeneity caused by imperfections of main superconducting coils and the cold head operation, typical for cryogen-free magnets. For the dynamic inhomogeneity, we apply a variant of the general reference deconvolution method, complemented with our mathematical analysis of spectral parameters.

Cryogen-free 400 MHz (9.4 T) solid state MAS NMR system with liquid state NMR potential.

We show that the temporal magnetic field distortion generated by the Cold Head operation can be removed and high quality Solid-State Magic Angle Spinning NMR results can be obtained with a cryogen-free magnet. The compact design of the cryogen-free magnets allows for the probe to be inserted either from the bottom (as in most NMR systems) or, more conveniently, from the top. The magnetic field settling time can be made as short as an hour after a field ramp.

A new method to measure the temporal magnetic field instabilities in cryogen-free magnets for magnetic resonance.

Despite the obvious advantages of cryogen-free magnets for NMR such as independence of liquid helium supply and the possibility to use the same magnet at different fields, the practical application of those magnets remains limited because of temporal magnetic field distortions associated with cryogen-free cold head operation. A new experimental method for the simple and reliable detection of the temporal field distortions is described in this paper. The accuracy of the magnetic field measurements by this method is two orders of magnitude higher than by conventional MetroLab Tesla meter.

A method for fast field settling in cryogen-free superconducting magnets for NMR.

We propose a fast algorithm to energise a cryogen free magnet to a highly persistent state. A decay rate as low as 0.021 ​ppm/h can be achieved in less than an hour after reaching the target field.

On the magnetic field stability of cryogen-free magnets for magnetic resonance applications.

The temporal magnetic field variation associated with Cold Head operation in cryogen-free magnets was studied. Three different mechanisms for such variations were tested separately and rated by their importance. It was found that mechanical displacement of the magnet inside the cryostat is the main issue of magnetic field perturbation.

A spectrometer designed for 6.7 and 14.1 T DNP-enhanced solid-state MAS NMR using quasi-optical microwave transmission.

A Dynamic Nuclear Polarisation (DNP) enhanced solid-state Magic Angle Spinning (MAS) NMR spectrometer operating at 6.7 T is described and demonstrated. The 187 GHz TE(13) fundamental mode of the FU CW VII gyrotron is used as the microwave source for this magnetic field strength and 284 MHz (1)H DNP-NMR.

Determination of the temperature dependence of the dynamic nuclear polarisation enhancement of water protons at 3.4 Tesla.

It is shown that the temperature dependence of the DNP enhancement of the NMR signal from water protons at 3.4 T using TEMPOL as a polarising agent can be obtained provided that the nuclear relaxation, T(1I), is sufficiently fast and the resolution sufficient to measure the (1)H NMR shift. For high radical concentrations (∼100 mM) the leakage factor is approximately 1 and, provided sufficient microwave power is available, the saturation factor is also approximately 1.

DNP enhanced NMR using a high-power 94 GHz microwave source: a study of the TEMPOL radical in toluene.

DNP enhanced (1)H NMR at 143 MHz in toluene is investigated using an NMR spectrometer coupled with a modified EPR spectrometer operating at 94 GHz and TEMPOL as the polarisation agent. A 100 W microwave amplifier was incorporated into the output stage of the EPR instrument so that high microwave powers could be delivered to the probe in either CW or pulsed mode. The maximum enhancement for the ring protons increases from approximately -16 for a 5 mM TEMPOL solution to approximately -50 for a 20 mM solution at a microwave power of approximately 480 mW.