Electron self-injection into an evolving plasma bubble: Quasi-monoenergetic laser-plasma acceleration in the blowout regime

Abstract

Electron self-injection into an evolving plasma bubble: Quasi-monoenergetic laser-plasma acceleration in the blowout regime" (2011 An electron density bubble driven in a rarefied uniform plasma by a slowly evolving laser pulse goes through periods of adiabatically slow expansions and contractions. Bubble expansion causes robust self-injection of initially quiescent plasma electrons, whereas stabilization and contraction terminate self-injection thus limiting injected charge; concomitant phase space rotation reduces the bunch energy spread. In regimes relevant to experiments with hundred terawatt-to petawatt-class lasers, bubble dynamics and, hence, the self-injection process are governed primarily by the driver evolution. Collective transverse fields of the trapped electron bunch reduce the accelerating gradient and slow down phase space rotation. Bubble expansion followed by stabilization and contraction suppresses the low-energy background and creates a collimated quasi-monoenergetic electron bunch long before dephasing. Nonlinear evolution of the laser pulse (spot size oscillations, self-compression, and front steepening) can also cause continuous self-injection, resulting in a large dark current, degrading the electron beam quality.

Generation of Superponderomotive Electrons in Multipicosecond Interactions of Kilojoule Laser Beams with Solid-Density Plasmas

“…So electrons always experience longer and larger antidephasing than dephasing. From the viewpoint of a non-stationary Hamiltonian theory [31][32][33][34], antidephasing (resulting in a high-energy electron acceleration) may be interpreted as a reduction of the "moving-frame" Hamiltonian, , , where γ e = (1 + p 2 /m e 2 c 2 + a 0 2 /2) 1/2 .…”

Sub-millimeter-scale, 100-MeV-class quasi-monoenergetic laser plasma accelerator based on all-optical control of dark current in the blowout regime

“…First, short dephasing length reduces the energy gain in a dense plasma. Secondly, massive continuous self-injection (dark current), destroys electron beam quality long before dephasing [7,8]. Both difficulties have the same underlying cause.…”

“…Electron cavitation relaxes limitations on the charge imposed by beam loading [4]. The bubble readily traps relativistic electrons from its sheath [1,5,6,7], reducing the technical complexity of the experiment while preserving flexibility in parameters [2,5,7]. Robustness of self-injection is rooted in the adiabatically slow evolution of the bubble, which, in turn, is tied to the nonlinear optical evolution of the driver [5,6,7,8].…”

“…Anomalous group velocity dispersion (GVD) of radiation in a plasma slows down the red-shifted head, eventually compressing the pulse into a few-cycle-long relativistic optical shock (ROS) [10]. Not only does formation of the ROS slow down the pulse, reducing the dephasing length, decreasing the energy gain [1]; it also causes constant expansion of the bubble, trapping copious amounts of unwanted electrons, and producing a poorly collimated, polychromatic energy tail completely dominating the spectrum [7,14,15]. We proposed to suppress formation of the ROS by using a broad bandwidth [corresponding to a few-cycle transformlimited duration (TLD)] negatively chirped pulse [8].…”

“…The bubble readily traps relativistic electrons from its sheath [1,5,6,7], reducing the technical complexity of the experiment while preserving flexibility in parameters [2,5,7]. Robustness of self-injection is rooted in the adiabatically slow evolution of the bubble, which, in turn, is tied to the nonlinear optical evolution of the driver [5,6,7,8]. Therefore, controlling relativistic optical phenomena, such as self-focusing [9], phase self-modulation and pulse self-compression [10], provides an opportunity to manage the fully kinetic self-injection process and optimize electron beam parameters [8,11].…”