Electron Retarding Potential Analyzer (ERPA)

The Electron Retarding Potential Analyzer (ERPA) is a retarding potential analyzer designed to measure thermal electrons from 0.06 eV to 3 eV with a resolution of 0.06 eV. ERPA is a compact version of the traditional RPA that utilizes multiple baffle collimators in its design. As with previous RPAs, ERPA collects ambient electrons by applying a sweeping voltage across its aperture in order to repel electrons below a certain energy threshold and accept electrons with energy greater.  The electrons that reach the central anode produce a measureable current that is then processed through a low-noise electrometer circuit to determine the electron temperature.   Since its first mission in 2004, ERPA has been flown on multiple missions including SERSIO (35.035), SCIFER (40.021), ROPA (40.020), ACES (36.242), MICA (36.273), RENU2 (52.002), KiNET-X (52.007), CREX-2 (52.006), and LAMP (36.351). Each of these missions operated successfully and have returned excellent data.

photos by Hyomin Kim