Emittance measurements of space‐charge‐dominated electron beams

A diagnostic technique for measuring beam emittance is developed for electron beams with diverging envelopes under strong space‐charge forces. Radial profiles of current density, local temperature, and divergence angle are measured by the slit–pinhole method for axisymmetric beams. The particle distribution function in transverse phase space is then constructed and the rms emittance is obtained by numerical integrations. A 5‐kV, 200‐mA, 3‐μs, and 60‐pps electron beam is used in the comparison between theory and this experimental diagnostic method.