A retarding field energy analyzer has been developed for diagnosing 300 &mgr;s duration, 60 cm×60 cm negative glow, sheet plasmas immersed in a 150–250 G axial magnetic field. The electron density in these 4.5 kV, 13 A, 120 mTorr discharges in air and other gases, is high enough to reflectX‐band microwaves. The presence of the magnetic field makes the suppression of secondary electrons from the Faraday collector surface more difficult. The approach taken here is to bias the entire collection circuit and the amplifiers 90 V positive with respect to the data acquisition room. The differentially pumped analyzer is designed to accept electrons with a large range of perpendicular velocities, and it measures the parallel velocity distribution function of the discharge electrons entering a 0.64‐mm‐diam hole in the anode plate. It gives valuable information about the energy spectrum of the energetic beam electrons emitted from the cathode, and the effect of energy loss and scattering processes on this propagating beam component. Additionally, since the analyzer sampling hole is offset from the anode‐cathode axis, the current density profile can be measured for different bias voltages on the retarding grid, by rotating the linear cathode about the vertical anode‐cathode axis. These profiles give the sheet thickness for the beam and plasma components of the negative glow discharge. It also gives useful information about the scattering induced beam spreading and its effects on the plasma sheet thickness and electron density. ©1996 American Institute of Physics.