Using Laser-Induced Rydberg Spectroscopy diagnostic for direct measurements of the local electric field in the edge region of NSTX/NSTX-U: Modeling.

ABSTRACT

We discuss a novel diagnostic allowing direct measurements of the local electric field in the edge region of NSTX/NSTX-U. This laser based diagnostic's principle consists of depleting the naturally populated n = 3 level to a Rydberg state-sensitive to electric fields-that will result in a suppression of part of the D α emission. We refer to this approach as Laser-Induced Rydberg Spectroscopy. It is shown that the local electric field can be measured through the Stark induced resonances observed as dips in the D α emission. Using forward-modeling of simulated absorption spectra, we show precisions reaching ±2 kV m-1 in regions with a local electric field of 15 kV m-1.