Abstract
We describe the design and construction of an electron gun which produces a 1 mm focused beam with a 5° full width of angular convergence. The maximum achievable beam current depends on the energy, υ0, and is given as Imax ⋍ 0.1 (μA/V3/2) × V03/2. The gun is used in inverse photoelectron spectroscopy (IPES), and is operated at energies as low as 5 eV. The gun employs a BaO cathode operating at 850–1100°C. The low thermal energy spread of the beam (kT ≈ 0.1 eV) and the narrow convergence angle are ideal for momentum resolved IPES. The focused beam is well suited for use with a grating spectrograph IPES detector.The output beam parameters could easily be modified, within certain fundamental constraints, to suit purposes other than IPES. The design principles and the factors controlling beam parameters are discussed in detail.
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