Effect of driver charge on wakefield characteristics in a plasma accelerator probed by femtosecond shadowgraphy

Schöbel, Susanne and Pausch, Richard and Chang, Yen-Yu and Corde, Sébastien and Couperus Cabadağ, Jurjen and Debus, Alexander and Ding, Hao and Döpp, Andreas and Foerster, F Moritz and Gilljohann, Max and Haberstroh, Florian and Heinemann, Thomas and Hidding, Bernhard and Karsch, Stefan and Köhler, Alexander and Kononenko, Olena and Kurz, Thomas and Nutter, Alastair and Steiniger, Klaus and Ufer, Patrick and Martinez de la Ossa, Alberto and Schramm, Ulrich and Irman, Arie (2022) Effect of driver charge on wakefield characteristics in a plasma accelerator probed by femtosecond shadowgraphy. New Journal of Physics, 24 (8). 083034. ISSN 1367-2630 (https://doi.org/10.1088/1367-2630/ac87c9)

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Abstract

We report on experimental investigations of plasma wave structures in a plasma wakefield acceleration (PWFA) stage which is driven by electron beams from a preceding laser plasma accelerator. Femtosecond optical probing is utilized to allow for direct visualization of the plasma dynamics inside the target. We compare two regimes in which the driver propagates either through an initially neutral gas, or a preformed plasma. In the first case, plasma waves are observed that quickly damp after a few oscillations and are located within a narrow plasma channel ionized by the driver, having about the same transverse size as the plasma wakefield cavities. In contrast, for the latter robust cavities are recorded sustained over many periods. Furthermore, here an elongation of the first cavity is measured, which becomes stronger with increasing driver beam charge. Since the cavity length is linked to the maximum accelerating field strength, this elongation implies an increased field strength. This observation is supported by 3D particle-in-cell simulations performed with PIConGPU. This work can be extended for the investigation of driver depletion by probing at different propagation distances inside the plasma, which is essential for the development of high energy efficiency PWFAs.

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