Electron trajectories and betatron oscillation in the wake bubble in laser-plasma interaction

Abstract

The trajectories of electrons originating from different initial locations in the unperturbed plasma during the interaction of an ultraintense laser with underdense plasma in the bubble regime are followed by particle-in-cell simulation. It is found that plasma electrons initially aligned with the rim of the laser focal spot contribute most to the bow wave in front of the bubble and those aligned with the lateral bubble sheath edge contribute most to the self-injection at the back of the bubble. A scaling law between the transverse electric and magnetic fields for the case where there are many electrons in the bubble is given and discussed in terms of betatron oscillations of the injected electrons.

Physics of Quasi-Monoenergetic Laser-Plasma Acceleration of Electrons in the Blowout Regime

“…2(c). Figure 2(g) indicates that, in agreement with earlier studies (Pukhov et al, 2010;Tsung et al, 2006;Wu et al, 2009), only electrons with impact parameters such that they enter the sheath are collected and accelerated. And, the condition (2) always holds, sometimes rather closely, when self-injection occurs in low-density plasmas, γ g > 65 (Kalmykov et al, 2009;2011a).…”

Bubble core field modification by residual electrons inside the bubble

“…1 Since then many works have been contributed to this interesting research field of laser-driven plasma wakefield acceleration, particularly in the research direction of the so-called bubble regime, [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] which can produce nearly monoenergetic fast electrons. In this regime, the ponderomotive force of a short intense laser pushes away almost all the plasma electrons and forms an electron cavity or bubble.…”

Computationally efficient methods for modelling laser wakefield acceleration in the blowout regime

“…Given sufficient computing power, electromagnetic PIC codes can simulate the plasma electrons (and ions, if necessary), the laser pulse driving the plasma wake, and the dynamics of electrons injected into the accelerating potential. In particular, two-and three-dimensional PIC simulations have been essential in understanding the dynamical nature of the electron self-injection process (Xu et al 2005;Oguchi et al 2008;Wu et al 2009;Zhidkov et al 2010;Kalmykov et al 2009Kalmykov et al , 2010Kalmykov et al , 2011a. However, to capture precisely the correlation between driver dynamics, elec-tron self-injection, and GeV-scale acceleration in the bubble regime, a simulation must meet a number of challenging requirements.…”

“…The need to resolve the laser wavelength, λ 0 ∼ 1 µm, fixes the grid resolution, and, due to stability conditions (Courant et al 1967), also limits the time step to a small fraction of ω −1 0 . Furthermore, the strong localisation of the injection process imposes even stricter limit on grid resolution; the vast majority of injection candidates are concentrated in the inner lining of the bubble (the sheath), and penetrate into the bubble near its rear, where the sheath is longitudinally compressed to a few tens of nanometres (Wu et al 2009;Kalmykov et al 2011a). Resolving this structure, together with ensuring sufficient particle statistics in the sheath, is necessary to avoid excessive sampling noise and eliminate unphysical effects.…”