The efficiency of detecting H and D atoms (E<1 keV) escaping a plasma has been increased by use of a cesium vapor cell to form negative ions by electron attachment collisions. A 30 cm long heat pipe confines the cesium to a localized region. The resulting negative ions are energy analyzed with a single‐channel, parabolic parallel‐plate analyzer and detected by a channel multiplier. The H0conversion efficiency was 10−2at 100 eV, increasing to 3.8×10−2at 500 eV. For a H0energy of 100 eV, the analyzer is 2.5 orders of magnitude more efficient than a comparable N2stripping cell analyzer. The analyzer has been used to measure ion temperatures as low as 30 eV on the EBT Plasma experiment.