In the plasma wakefield acceleration (PWFA) experiment two 60 MeV sub-picosecond electron bunches were transported through plasma produced by a capillary discharge. Both bunches are shorter than the plasma’s wavelength, and phasing of the second bunch into the plasma wave is adjusted by tuning the plasma’s density. It is shown that the second bunch experiences a 150 MeV/m loaded accelerating gradient in the wakefield driven by the first bunch (see figures).
Figure 1. Layout of the double-bunch PWFA experimental setup
Figure 2. Experimental data points for the energy shift of the witness electron-bunch centroid for a range of plasma densities; the solid curve represents our 2D numerical calculations.
This was the first experiment to directly demonstrate the high-gradient, controlled acceleration of a short electron bunch trailing the driver electron bunch in high density plasma. The method constitutes a promising step towards producing monoenergetic bunches in next-generation ultra high-gradient plasma accelerators.
Kallos, E., et al., High-Gradient Plasma-Wakefield Acceleration with Two Subpicosecond Electron Bunches. Phys. Rev. Lett., 2008. 100(7): p. 074802. 79.