Electron bunch generation from a plasma photocathode

Deng, Aihua and Karger, Oliver and Heinemann, Thomas and Knetsch, Alexander and Scherkl, Paul and Manahan, Grace Gloria and Beaton, Andrew and Ullmann, Daniel and Wittig, Gregor and Habib, Ahmad Fahim and Xi, Yunfeng and Litos, Mike Dennis and O'Shea, Brendan D. and Gessner, Spencer and Clarke, Christine I. and Green, Selina Z. and Lindstrøm, Carl Andreas and Adli, Erik and Zgadzaj, Rafal and Downer, Mike C. and Andonian, Gerard and Murokh, Alex and Bruhwiler, David Leslie and Cary, John R. and Hogan, Mark J. and Yakimenko, Vitaly and Rosenzweig, James B. and Hidding, Bernhard (2019) Electron bunch generation from a plasma photocathode. Preprint / Working Paper. arXiv.org, Ithaca, N. Y..

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Plasma waves generated in the wake of intense, relativistic laser or particle beams can accelerate electron bunches to giga-electronvolt (GeV) energies in centimetre-scale distances. This allows the realization of compact accelerators having emerging applications, ranging from modern light sources such as the free-electron laser (FEL) to energy frontier lepton colliders. In a plasma wakefield accelerator, such multi-gigavolt-per-metre (GV m$^{-1}$) wakefields can accelerate witness electron bunches that are either externally injected or captured from the background plasma. Here we demonstrate optically triggered injection and acceleration of electron bunches, generated in a multi-component hydrogen and helium plasma employing a spatially aligned and synchronized laser pulse. This ''plasma photocathode'' decouples injection from wake excitation by liberating tunnel-ionized helium electrons directly inside the plasma cavity, where these cold electrons are then rapidly boosted to relativistic velocities. The injection regime can be accessed via optical density down-ramp injection, is highly tunable and paves the way to generation of electron beams with unprecedented low transverse emittance, high current and 6D-brightness. This experimental path opens numerous prospects for transformative plasma wakefield accelerator applications based on ultra-high brightness beams.