Applications of Superconducting Solenoids

An instrumental development of considerable importance to the p.m.r. spectroscopy of carbohydrates has been the introduction of high-resolution magnets based on superconducting solenoids.47 As already mentioned, the (homogeneous) magnetic field-intensity in conventional electromagnets is restricted by the properties of the iron core and by the fact that the addition of auxiliary coils that are 

The magnetic field inside a superconducting solenoid is not particularly homogeneous, and compensation of the field gradients is quite a complex problem that has been solved49 by the provision of mathematically designed arrays of superconducting or normal, resistive shim-coils, or both. 

The high cost of the first 220-MHz spectrometers and their restriction, at least initially, to observation of protons only (in 5-mm sample tubes) and to field-sweep operation, has encouraged a number of research groups51 outside the spectrometer industry to construct 

The high cost of commercial superconducting spectrometers and of the continuing supply of liquid helium needed has limited the number of installations of these instruments, and, in some countries, such high-frequency p.m.r. spectra are available only from a national service center. However, some savings are realized because of the fact that, once established in the persistent mode, superconducting solenoids require neither a power supply nor cooling water. 

Further improvements in superconducting materials50 permitted the development in 1970 of a 300-MHz spectrometer that is equipped with a low-loss Dewar vessel, an improved sweep-system that allows both field sweeps and frequency sweeps up to a maximum width of 20 kHz, and accessories for a variety of nuclei and pulse-Fourier-transform techniques. 

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