High-power microwave field measurements using Stark broadening

High power microwave sources driven by intense relativistic electron beams have been a subject of much research over the last decade. In the course of research upon the issues of RF breakdown, we have developed a diagnostic capable of measuring high RF power levels in high electric field regions. This diagnostic takes advantage of the RF Stark effect. To investigate the effect, a hydrogen-filled glass tube is placed in a region of high RF power. When an RF pulse impinges on the tube, the gas in the tube is excited. By spectral observations of the decay of the gas back to the ground state, the Stark splitting of the atomic states can be measured. This splitting is proportional to both the RF electric field amplitude and frequency. In this paper we present results from a series of experiments performed at the Phillips Laboratory on the relativistic klystron. Spectral measurements were performed in the near field of the radiating antenna using an optical multi-channel analyzer with a half-meter spectrograph. These experiments demonstrate that Stark broadening can be a useful diagnostic in high field environments.