Prospects and limitations of wakefield acceleration in solids

Advances in the generation of relativistic intensity pulses with wavelengths in the X-ray regime, through high harmonic generation from near-critical plasmas, open up the possibility of X-ray driven wakefield acceleration. The similarity scaling laws for laser plasma interaction suggest that X-rays can drive wakefields in solid materials providing TeV/cm gradients, resulting in electron and photon beams of extremely short duration. However, the wavelength reduction enhances the quantum parameter χ, hence opening the question of the role of non-scalable physics, e.g., the effects of radiation reaction. Using three dimensional Particle-In-Cell simulations incorporating QED effects, we show that for the wavelength λ=5  nm and relativistic amplitudes a0=10–100, similarity scaling holds to a high degree, combined with χ∼1 operation already at moderate a0∼50, leading to photon emissions with energies comparable to the electron energies. Contrasting to the generation of photons with high energies, the reduced fr...