Abstract
In this paper, we propose to manipulate a nonrelativistic electron beam during its emission and acceleration to create nanobunched electrons. Specifically, we simulate the acceleration of a structured electron beam emitted from a multiring photocathode in a photoinjector and show that, after acceleration, such a transversely structured beam can be transformed into a hollow beam with a longitudinal density modulation in the petahertz frequency range. Our theoretical study shows that, in the far-field zone, the coherent radiation of the bunched hollow beam approaches that of a similarly bunched solid beam in the paraxial limit.
Highlights
It is well known that an electron beam having a length much longer than the desired radiation wavelength emits incoherent radiation with spectral energy linearly proportional to the number of electrons in the beam
We simulate the acceleration of a structured electron beam emitted from a multiring photocathode in a photoinjector and show that, after acceleration, such a transversely structured beam can be transformed into a hollow beam with a longitudinal density modulation in the petahertz frequency range
For a 100-fC electron beam with an initial Lorentz factor γ ∼ 1 uniformly distributed over a two-dimensional disk within a radial distance r 1⁄4 2 mm, the space charge field at the center of the disk surface is about Esc ∼ 449.39 V=m, which is significantly smaller than the nominal tens of MV=m accelerating field in an accelerator
Summary
It is well known that an electron beam having a length much longer than the desired radiation wavelength emits incoherent radiation with spectral energy linearly proportional to the number of electrons in the beam. We analytically calculate and compare the bunching factors of a hollow and a solid beam with the same longitudinal density modulation As it will be shown below, the comparison indicates that the far-field coherent radiation of the hollow beam generated by our scheme is similar to that of a solid beam in the paraxial limit
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