Numerical simulations of early-stage dynamics of electron bunches emitted from plasmonic photocathodes

Abstract

High-brightness electron sources are a key ingredient to the development of compact accelerator-based light sources. The electron sources are commonly based on (linear) photoemission process where a laser pulse with proper wavelength impinges on the surface of a metallic or semiconductor photocathode. Very recently, the use of plasmonic cathodescathodes with a nano-patterned surface -have demonstrated great enhancement in quantum efficiencies [1]. Alternatively, this type of photocathodes could support the formation of structured beams composed of transversely-separated beamlets. In this paper we discuss numerical simulations of the early-stage beam dynamics of the emission process from plasmonic cathodes carried out using the Warp [2] framework. The model is used to investigate the properties of beams emitted from these photocathode and subsequently combined with particle-in-cell simulations to explore the imaging of cathode pattern after acceleration in a radiofrequency gun.

Design of the Low-Energy DC Gun for Field-Emission Cathode Investigation

“…The latter quadrupole magnets will be used to image the beam and check some of the beam-matching conditions derived in Ref. [6] while also enabling the transverse-emittance measurement using the quadrupole-scan method. Ultimately, the system will support the investigation and characterization (I − V curve, emittance, lifetime) of an array of silicon-based FE cathodes (e.g.…”

“…The cathode located at z = 0 m is modeled as a field-emission source following the model described in Ref. [6]. To avoid modeling the specific nanostructure of the cathode, for sake of speed and memory demand, we introduce a field-enhancement factor β e ≡ E surf /E mac as the ratio of the macroscopic field E mac associated with the cathode-anode geometry with an enhanced surface field E surf owing to the emitting surface microscopic geometry.…”

“…The electron sources with the FE cathodes can be anticipated to provide extremely high brightness corresponding to the quantum-limited emittance ε q ≡ N λ3 c /2, where N is the number of electrons and λc is the Compton wavelength. Additionally, an array of regularly-organized tips provides a source of transversely-segmented electron beamlets which could be subsequently manipulated for advanced applications [5], [6].…”