Abstract
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 frequency of photon emission at X-ray wavelengths (compared with that at optical wavelengths) leads to a reduction in the amount of energy that is removed from the electron population through radiation reaction. Furthermore, as the emission frequency approaches the laser frequency, the importance of radiation reaction trapping as a depletion mechanism is reduced, compared with that at optical wavelengths for a0 leading to similar χ.
Highlights
The generation of a wake structure by the interaction of an optical laser pulse with an underdense plasma has been demonstrated to accelerate electrons to GeV energies.[1–4] For sufficiently high laser amplitudes, the laser pulse expels the electrons from a region, forming a cavity that traps electrons which are accelerated to high energies and oscillate in the transverse field structure, emitting photons in the Xray and c range
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
Using three dimensional Particle-In-Cell simulations incorporating QED effects, we show that for the wavelength k 1⁄4 5 nm and relativistic amplitudes a0 1⁄4 10–100, similarity scaling holds to a high degree, combined with v $ 1 operation already at moderate a0 $ 50, leading to photon emissions with energies comparable to the electron energies
Summary
The generation of a wake structure by the interaction of an optical laser pulse with an underdense plasma has been demonstrated to accelerate electrons to GeV energies.[1–4] For sufficiently high laser amplitudes, the laser pulse expels the electrons from a region, forming a cavity that traps electrons which are accelerated to high energies and oscillate in the transverse field structure, emitting photons in the Xray and c range. E.g., k 1⁄4 800 nm, the critical plasma density nc 1⁄4 mex2=4pe2 1⁄4 1:7 Â1021 cmÀ3, where me is the electron mass, e is the electron charge, and x is the angular frequency of the laser radiation. This density is orders of magnitude lower than that of solid density materials, which renders solids unfeasible for wakefield acceleration using contemporary optical laser systems. The short wavelength enhances the quantum parameter v This could lead to a highly efficient radiation source of high energy photons even at moderate relativistic amplitudes a0 1⁄4 eE=mecx, where c is the speed of light and E is the electromagnetic field strength
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