Anomalous Energy Spreads in Electron Beams

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Abstract
Energy distributions of 2‐ to 10‐eV electron beams were measured in a deflection analyzer. The performance of the analyzer was monitored by use of a second one in tandem. In agreement with earlier measurements in high‐energy beams the energy distribution varied with current. At low beam currents the energy distribution was Maxwellian at a temperature corresponding to the cathode temperature. As the current increased toward the beam space‐charge limit, the energy width increased. The excess energy width could be fitted to a curve linear in current density and varying inversely with beam energy to the three‐halves power. No shift in most probable energy was found. The results are not in quantitative agreement with the higher‐energy low space‐charge measurements.