High-Flux Betatron X-ray Generation from Beam-Loading-Assisted Laser Wakefield Acceleration in Density-Tailored Plasmas

The density profile consists of a two-section longitudinal up-ramp, with a gradual increase in a low-density region followed by a sharp rise near the capillary exit, enabling coordinated control of electron acceleration and betatron oscillations. In the low-density region, the gradual density increase keeps electrons in the accelerating phase, producing GeV-class beams and inducing strong beam loading that reshapes the wakefield.

The rapid density rise near the capillary exit further enhances betatron oscillations, leading to synergistically enhanced radiation. With this scheme, an average flux exceeding 1014 photons per steradian above 5 keV, an order of magnitude higher than the earlier reports, along with the critical energy 72±8 keV, and a full width at half maximum divergence (6.1±1.9)×(5.8±1.6) mrad2 of betatron radiation were experimentally obtained.