High-Q Stark Cavity Absorption Cell for Microwave Spectrometers

Abstract

Design considerations, description, and some data on the performance are given of a large pillbox‐shaped Stark cavity absorption cell for the 1.25‐cm wavelength region. The cavity can be used in any TE_0m1 mode with m ranging from about 5 to about 12 and its most prominent features are: high loaded Q factor (∼5×10³−10⁴), good electric insulation (at pressures below 4×10⁻² mm Hg Stark voltages up to 3000 v can be applied), low Stark field inhomogeneity (diameter to length ratio 15–20), large band width (from about 18 to about 28 kMc), and low mode density. No cross‐mode resonances occur and the only undesired modes excited appreciably are the TE_2m1 ones. When used in transmission only the TE_0m1 modes couple to the output. The cavity can be used at the same time as a reference cavity of a Pound‐type klystron frequency stabilizer. The klystron frequency will then automatically follow the resonance frequency of the cavity over a frequency interval up to 400 Mc.