With a careful choice of the viewing parameters, neutral-particle analysers could be used to detect small changes in the radial electric field Er immediately next to the separatrix with a submillisecond (50-100 µs) resolution. In particular, the poloidal viewing angle has to be optimized according to the ripple- and plasma geometry. In addition, the use of a small diagnostic beam is proposed to improve the signal level and quality.
Kurki-Suonio, T., Sipilä, S., & Heikkinen, J. (2000). Active diagnostic of edge Er using neutral-particle analysers. Plasma Physics and Controlled Fusion, 42(Supplement 5A), A277-A282. https://doi.org/10.1088/0741-3335/42/5A/333