An X0 shim coil for precise magic-angle adjustment.

A new method for precise setting of the spinning angle to the magic angle by using a saddle coil is described. The coil, which is referred to as an X 0 shim coil, is wound to produce a uniform static magnetic field B x perpendicular to the main magnetic field B 0 . The magnetic field felt by a sample is a vector sum of the main field B 0 and the transverse field B x produced by the X 0 shim coil. Hence the angle between the spinner axis and the effective magnetic field can be controlled by current I supplied to the X 0 shim coil, leading to precise angle adjustment without backlash accompanied with a mechanical system conventionally used. It is shown that the angle range achieved is ± 0.05 ° for I = ± 5 A at B 0 = 7 T. [ABSTRACT FROM AUTHOR]