Self-focusing and dense gamma rays in electron beam-multifoil collisions

When a highly compressed and focused electron beam collides with a solid-density plasma, electromagnetic fields associated to the near field of transition radiation are generated near the surface and they are strong enough to further focus the beam and induce intense gamma-ray emission by the high-energy electron beam [1, 2]. This effect can be considerably enhanced in electron beam-multifoil collisions, where the beam collides with a sequence of solid-density plasmas leading to steadily increasing focusing and highly efficient gamma-ray generation (see figure below), with the electron beam and gamma-ray beam ultimately exceeding solid density and the interaction entering the strong-field QED (SFQED) regime [1].

This novel concept, reported in Phys. Rev. Lett [1] and developed with MPIK, CEA and other collaborators, is also the object of a new experiment led by Matteo Tamburini (MPIK) and Sébastien Corde (LOA) that was recently proposed and approved by the FACET-II accelerator facility at SLAC. This new E-332 experiment is expected to take its first measurements starting from mid-2021. With parameters expected to be achieved by the facility, the gamma-ray radiation yield could exceed 10% of the total electron beam energy (see figure below).

[1] A. Sampath et al., Extremely Dense Gamma-Ray Pulses in Electron Beam-Multifoil Collisions, Phys. Rev. Lett. 126, 064801 (2021).

[2] S. Corde et al., Beam focusing by near-field transition radiation, Research Report hal-02937777v2 (2020),

Figure: (top) Schematic of the concept of self-focusing and generation of gamma rays in electron beam-multifoil collisions. (bottom) Results of a CALDER-circ PIC simulation of a 10 GeV, 2 nC electron beam with 1-micron bunch length and 5-micron beam size impinging on a single Al foil (red dashed line) followed by a stack of Al foils (red shaded area). The phase space of electron beam after 1st foil (bottom left) shows the focusing effect induced by beam-foil collision, and the evolution of beam size and radiation yield (bottom right) illustrate self-focusing and highly-efficient generation of gamma rays. Figure from Refs [1] and [2].