Tuning Shims for 10-5 Field Quality at 2/3 of coil radius
Basic Principle of Tuning Shims:
Magnetized iron shims modify the magnet harmonics.
Eight measured harmonics are corrected by adjusting the amount of iron in eight Tuning Shims.
Procedure for using tuning shims in a magnet:
1. Measure field harmonics in a magnet.
2. Determine the composition of magnetic iron (and remaining non-magnetic brass) for each of the eight tuning shim. In general it would be different for each shim and for each magnet.
3. Install tuning shims. The tuning shims are inserted without opening the magnet (if the magnet is opened and re-assembled again, the field harmonics may get changed by a small but a significant amount).
4. Measure harmonics after tuning shims for confirmation.
GOAL : Make field errors in magnets much smaller than that is possible from the normal tolerances.