Falsification by space charge of electron beam energy measurements

Abstract

When the energy of the electrons in a beam is determined by noting the value of a stopping potential that cuts off the beam, the current density of the beam must be below a limiting value determined by space charge considerations. Above this limit, cutoff occurs sharply at a voltage that may be far below the potential that accelerates the beam. At stopping potentials above cutoff, a weak tail of current does persist all the way up to the full potential of the beam.