Grounding, DC Supplies, and Controlling Signal Issues for a Tunable Reflectometry System

Reflectometry, which uses the microwave radar technique to probe the magnetically confined fusion plasmas, is a very powerful tool to observe the density fluctuations in the fusion plasmas. Typically, two or more microwave beams of different frequencies are used for this purpose. If the intention is to study the plasma density correlations in real time, a tunable microwave source of finite bandwidth with real time control system will be desired. Because the tunable microwave source assembly and other sources as well as amplifiers in the system usually require multiple dc voltage supplies, different grounding schemes and filtering to break the ground loops have to be implemented in order to guarantee the system performance. In this paper, these grounding problems and the system performance impacts will be discussed while designing a new reflectometer with a tunable YIG oscillator for the Alcator C-Mod experiments.