182 / 2023-04-15 15:14:38

Pre-bunched electron beams generation in plasma accelerators

极端光下的基础物理学 > 粒子加速-II

The longitudinal coherence of X-ray free-electron lasers (XFELs) in the self-amplified spontaneous emission regime could be substantially improved if the high brightness electron beam could be pre-bunched on the radiated wavelength-scale. Here, we show that it is indeed possible to realize such current modulated electron beam at angstrom scale by exciting a nonlinear wake across a periodically modulated plasma-density downramp/plasma cathode. The density modulation turns on and off the injection of electrons in the wake while downramp provides a unique longitudinal mapping between the electrons’ initial injection positions and their final trapped positions inside the wake. The combined use of a downramp and periodic modulation of micrometers is shown to be able to produces a train of high peak current (10s of kA) electron bunches with a modulation wavelength of 10s of angstroms - orders of magnitude shorter than the plasma density modulation. The peak brightness of the nano- bunched beam can be O(10²¹A/m²/rad²) orders of magnitude higher than current XFEL beams. Such pre-bunched, high brightness electron beams hold the promise for compact and lower cost XEFLs that can produce nanometer radiation with hundreds of GW power in a 10s of centimeter long undulator.