High-performance field-emission electron gun using a reticulated vitreous carbon cathode

Abstract

Proof-of-concept experimental results stemming from beam simulations for a microfocus electron gun are presented. The simulations demonstrate the potential to produce 4 mA of current through a 40-μm-diameter spot, at an energy of 30 keV, emitted from a 1-mm-diameter cathode with low energy spread and high brightness. The experimental realization, scaled down for practicality, but consistent with and confirming the higher-energy simulation, produced 2 μA of current with an approximately 28 μm spot size at an energy of 9.3 keV. The electrons originated from an Ar+-ion-treated reticulated vitreous carbon (RVC) field-emission cathode shaped as an approximately 1-mm-diameter disk. The primary application for this work is a highly monochromatic microfocus x-ray source for use in phase-contrast imaging, although other beam applications exist. The use of an Ar+-ion-irradiated RVC cathode allows high, stable current at low electric field, superior to what is achievable using field-emitter arrays or carbon-nanotube cathodes. This method, scaled up to its maximum potential, also enables a high-current-density microfocus beam, which, to date, has not been demonstrated using thermionic cathodes. Such a beam applied to an x-ray source for phase-contrast imaging represents a significant benefit in medical diagnostics.