Abstract
The upgraded Accelerator Test Facility (ATF) ${\mathrm{CO}}_{2}$ laser located at Brookhaven National Laboratory offers a unique opportunity to investigate laser wakefield acceleration (LWFA) with a $10.6\mathrm{\text{\ensuremath{-}}}\ensuremath{\mu}\mathrm{m}$ laser, a wavelength where little experimental work exists. While long laser wavelengths have certain advantages over short wavelengths, our modeling analysis has uncovered another important effect. The upgraded ATF ${\mathrm{CO}}_{2}$ laser will have a pulse length as short as 2 ps. At a nominal plasma density of $\ensuremath{\sim}{10}^{16}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$, this pulse length would normally be considered too long for resonant LWFA, but too short for self-modulated LWFA. However, our model simulations indicate that a well-formed wakefield is nevertheless generated with electric field gradients of ${E}_{z}\ensuremath{\gtrsim}2\text{ }\text{ }\mathrm{GV}/\mathrm{m}$ assuming 2.5 TW laser peak power. The model indicates pulse steepening is occurring due to various nonlinear effects. It is possible that this intermediate laser pulse length mode of operation may permit the creation of well-formed, regular-shaped wakefields, which would be needed for staging the LWFA process. Discussed in this paper are the model, its predictions for an LWFA experiment at the ATF, and the pulse steepening effect.
Highlights
Laser wakefield acceleration (LWFA), whereby a highintensity laser pulse creates a plasma wake that can accelerate electrons, has demonstrated very high acceleration gradients of over 1 GV=m [1]
In this paper we describe the LWFA model, its modifications for simulating the Accelerator Test Facility (ATF) CO2 laser, and its predictions for an LWFA experiment that could be performed at the ATF
The principal result of this analysis is that a strong wake is excited even though the original laser pulse length is several times too long for efficient wake excitation by resonant LWFA
Summary
Laser wakefield acceleration (LWFA), whereby a highintensity laser pulse creates a plasma wake that can accelerate electrons, has demonstrated very high acceleration gradients of over 1 GV=m [1]. It is anticipated that the upgraded system will be able to produce 2 –10 ps laser pulses The availability of this upgraded laser source opens up the possibility to perform LWFA experiments at 10:6 m. The purpose of the modeling analysis and results presented in this paper is to predict the performance of a LWFA experiment performed at the ATF using the upgraded laser. This will provide a guide in planning such an experiment. Resonant LWFA normally requires the laser pulse length p to be comparable or less than half of the plasma wake period =!p, where !p / n1e=2 is the plasma frequency.
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