Laser wakefield acceleration using wire produced double density ramps

Abstract

A novel approach to implement and control electron injection into the accelerating phase of a laser wakefield accelerator is presented. It utilizes a wire, which is introduced into the flow of a supersonic gas jet creating shock waves and three regions of differing plasma electron density. If tailored appropriately, the laser plasma interaction takes place in three stages: Laser self-compression, electron injection, and acceleration in the second plasma wave period. Compared to self-injection by wave breaking of a nonlinear plasma wave in a constant density plasma, this scheme increases beam charge by up to 1 order of magnitude in the quasimonoenergetic regime. Electron acceleration in the second plasma wave period reduces electron beam divergence by % 25%, and the localized injection at the density downramps results in spectra with less than a few percent relative spread.

Localization of ionization-induced trapping in a laser wakefield accelerator using a density down-ramp

“…Several techniques to control the injection and trapping of electrons in an excited plasma wave have been demonstrated experimentally to decrease the shotto-shot fluctuations in charge and energy of the electrons in the generated beams. These methods include trapping by colliding pulses [9], trapping in density transitions [10,11] and downramps [7,12,13] and ionization-induced trapping [14,15].…”

Tunable monoenergetic electron beams from independently controllable laser-wakefield acceleration and injection

“…First, injection (and therefore charge and energy spread) could be controlled by the mixed-gas jet from the first nozzle. Our work differs from the works on down-ramp injection [18,19,[21][22][23], where only the position of injection was tuned, which did not extend to charge and energy spread tunability. Second, the acceleration length and gradient (and therefore electron energy) could be controlled by the length and density of the helium jet from the second nozzle.…”

“…There has been recent progress towards achieving this goal using the following approaches: (i) optical injection, involving two independent laser pulses, one to drive the wake and the other to inject electrons [13][14][15][16][17]; (ii) plasmaprofile tailoring, either by means of a machining laser pulse [18][19][20] or by the introduction of obstacles into the gas flow [21][22][23]; or (iii) the use of distinct media for injection and acceleration [24][25][26][27][28]. While these methods have resulted in tunable quasimonoenergetic electron beams, none of them were able to control the energy spread and charge as the beam was tuned in energy.…”

Control and optimization of a staged laser-wakefield accelerator

“…These methods do not rely on selftrapping, but instead involve deterministically forcing background plasma electrons to become locally dephased with respect to the wakefield and thus get trapped, and eventually accelerated by, the plasma wave. One implementation of this general concept involves the use of additional laser pulses [10][11][12][13]; while another involves the use of a density ramp [14][15][16][17][18][19][20]. Although the injector and accelerator stages were physically separated in some of these experiments [21][22][23][24][25][26][27], in the majority of cases, the injection and acceleration processes were not independently controlled, and consequently, neither were the electron beam parameters.…”