Bubble merging in laser wakefield acceleration as a way towards high-charge 1-GeV class electron beams

Le résumé fourni par la source

Abstract Laser wakefield acceleration offers ultra-high accelerating gradients, enabling compact sources of multi-GeV electron beams with femtosecond durations and quasi-monoenergetic spectra. In this work, we investigated the nonlinear evolution of plasma bubbles and their effect on electron injection and energy gain, using high-fidelity, multi-dimensional particle-in-cell (PIC) simulations performed with the open-source code SMILEI. A relativistically intense laser pulse ( a 0 =7.7, λ 0 =0.8 μ m, w 0 =20 μ m, E = 30 J, and τ = 30 fs) propagated through a helium gaseous medium with a plateau density of n e =7 × 10 18 cm −3 after complete ionization. The simulations revealed complex bubble dynamics, including initial formation, disruption, destruction, and bubble merging, strongly influenced by local longitudinal electric field E x approaching or exceeding the cold wave-breaking limit E WB . Exceeding the wave-breaking field E WB triggered bubble destabilization, while the bubble merging at the end of the plateau plasma density region extended the acceleration length, sustaining high longitudinal fields on the order of 1 TV m −1 and boosting continuous electron injection. This mechanism produced a dense, quasi-monoenergetic electron bunch with a charge of 1 nC, a peak energy of ∼1 GeV, femtosecond-scale duration, energy spread below 10%, rms angular divergence θ y of 7 mrad , and a longitudinal rms beam size of σ x = 10 μ m . Comprehensive analysis of the wakefield evolution demonstrated that exploiting nonlinear bubble evolution and interactions near the wave-breaking limit can enhance both energy gain and electron beam quality, providing actionable strategies for next-generation compact LPAs.

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