Supercon magnets

Using a horizontal 4.7 Tesla cryoshimmed supercon magnet with a bore diameter of 15 cm, we have obtained two-parameter mass calibrations with absolute mass accuracies of better than 1.5 ppm without, and better than 0.4 ppm with an internal calibrant over a mass range from 18 to 502 amu (10). Absolute accuracies with an internal calibrant are slightly better because the calibrant and the unknown compound are measured under identical physical conditions, in particular with the exact same number of ions in the cell, resulting in identical space-charge shifts (2). 

Due to the extreme stability of supercon magnets and the associated electronics, 2-3 ppm accuracies can be reproduced in the absence of reference compounds for many days. 

Another major challenge in supercon magnet technology is achievement of field uniformity. It should for example be borne in mind that In order to obtain a given line width at 500 MHz requires a 5 times better field homogeneity than at 100 MHz spectrometer frequency. Realization of say 0.1 Hz proton resolution, a value which has been achieved and surpassed, therefore demands the utmost In terms of workmanship and quality of material. This concerns, among other factors, constancy of wire diameter and uniformity of winding. In spite of these precautions, such ambitious objectives necessitate various forms of field corrections, whose detailed discussion however, would break the scope of this article. 

A dc SQUID is a device based on this effect, used for the measurement of microscopic magnetic fields. The acronym SQUID stands for supercon-... 

Superconductors are already being used to create high magnetic fields for use in instrumentation. But conventional supercon-... 

CePb has a simple cubic CujAu structure with a = 4.87 A. This compound has drawn much attention since Lin et al. (1985) reported that it exhibits, besides its HF properties and magnetic ordering at 7., 1.1 K, a magnetic-field-induced supercon-... 

Most modern NMR spectrometers employ large superconducting magnets, or supercons, as they are called. Very stable high fields, up to 21 T, or 900 MHz for the H resonance, are commercially available at this time. A superconducting magnet can be pictured as a set of concentric... 

C. King, A. van der Linden, Z. Melhem, P. Noonan, A. Twin, M. Field, S. Hong, J. Parrell and Y. Zhang, Development Trends in High Field Magnet Technology , IEEE Trans. Appl. Supercon., 2008, 18, 540. 

Fig. 47. Superconducting and ferromagnetic transition temperatures Tc (supercon.) and Tc (ferromagn.) as well as magnetic susceptibility at 0 K of Pr3Se4 La3Se4 mixed crystals versus composition.

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