176 / 2025-03-17 21:07:20

Three-dimensional nanoscale bunching of relativistic electron beam in plasma wakefield

relativistic electron beam,,plasma wakefields,micro-bunches,plasma focusing

Microbunching of relativistic electron beams (REBs) are relevant to many research areas as well as applications, such as attosecond electron diffraction, plasma-based accelerators (PBAs), inverse Compton scattering (ICS) sources, and X-ray free electron laser (XFEL).

We propose a simple and compact scheme to modulate a relativistic electron beam (REB) into three-dimensional (3D)

nanoscale bunches by injecting a rarefied REB into an underdense plasma. This scheme self-consistently integrates

the lateral focusing and axial modulation of REB in its self-driven plasma wakefield. The REB first expels the plasma

electrons in its path to form a wake, where the lateral force of the charge-separation field compresses it to higher density,

so that more plasma electrons are expelled as it propagates. The positive feedback loop is repeated until the REB

becomes a thin electron filament of density hundred times the original. As it continues to propagate in the elongated

electron-free wake bubble, the axial electric field induces an energy chirp on the electron filament, and longitudinally

modulates it into 3D nanoscale bunches by asynchronous envelope oscillations. The excitation conditions of this scheme

with respect to the beam and plasma parameters, as well as the spatial scale of obtained electron bunches, are analyzed

analytically and agree well with particle-in-cell simulations.