An Improved Technique for Measuring the Pierce Impedance of Helix Slow-Wave Structures

The Pierce impedance of helix slow-wave structures has been measured using nonresonant perturbation techniques. Effects of space harmonics and TE fields were demonstrated using experimental results for the first time. It was found that there was an error in the derivation of the correction factor commonly used for the uniform-axial-field assumption. It was shown that this error should be corrected at higher frequencies for accurate measurements. Using an automated set-up and improved experimental techniques the measurement repeatability of the existing technique has been improved from 5% to 2%.