Wavelength scaling and multi-color operation of a plasma driven attosecond X-ray source via harmonic generation

The generation of high power coherent soft X-ray pulses of sub-100 as duration and 10 nm wavelength using beams from a GeV energy plasma wakefield accelerator has been recently investigated in Ref. [arXiv:2011.07163]. As a future upgrade to this concept, this contribution investigates scaling to shorter X-ray wavelengths by cascading undulators tuned to higher harmonics of the fundamental. We present two simulation studies for plasma-driven attosecond harmonic generation schemes with final photon wavelengths of 2 nm and 0.40 nm. We demonstrate in these schemes that using undulators with retuned fundamental frequencies can produce GW-scale pulses of sub-nm radiation with tens of attosecond-scale pulse lengths, an order of magnitude shorter than current state-of-the-art attosecond XFELs. This multi-pulse multi-color operation will be broadly applicable to attosecond pump-probe experiments.