All critical circuit components, including the sample coils, are located
along with the spinner assembly in a region that may be evacuated to high
vacuum for thermal insulation and high-voltage operation. A hermetically
sealed spinner assembly simultaneously satisfies the requirements of
hermeticity, low total emissivity, rf compatibility, spinning
performance, magnetic compatibility, and high filling factor by utilizing
metal construction except for the central region near the rf sample
coils. Hence, it is possible to maintain high vacuum in the region
external to the MAS spinner assembly even over a broad range of bearing
and drive gas temperatures. A bundle of optical fibers is provided for
tachometry for spin rates up to 60 kHz. The use of alumina disc
capacitors allows the noise contributions from the most critical
capacitors to be reduced to a minor fraction of the total and simplifies
high voltage operation.