Accurate Shim-Coil Design and Magnet-Field Profiling by a Power-Minimization-Matrix Method
✍ Scribed by D.I. Hoult; R. Deslauriers
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 862 KB
- Volume
- 108
- Category
- Article
- ISSN
- 1064-1858
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✦ Synopsis
The design of a single correction coil that annuls, with minimal power consumption, the field inhomogeneity associated with a specific magnet is described. The design strategy used is also shown to be advantageous for the production of high-accuracy, power-efficient shim coils, "drift-free" shims (i.e., no slow mainfield drift following a change of shim current), and high-homogeneity "shielded" magnets. Starting with a description of field inhomogeneity in a spherical-harmonic basis set, the cylindrical-surface current-density function needed to annul inhomogeneity is calculated, with minimization of electrical power dissipation, by a simple matrix formulation. The inclusion of design constraints, such as the annulment of mutual inductance between zonal shims and the magnet, is highlighted and production of the current-density function with both wire and cut sheet is briefly discussed. Insights are presented as to why the method, unlike some, gives a smooth current-density function lacking spurious high-frequency ripples, and experimental and numerical tests are reported that reveal the efficacy of the computational procedures. C 1994 Academic Press, Inc.