Abstract
We report the first comprehensive study of large amplitude Langmuir waves in a plasma of nanometer-scale clusters. Using an oblique angle single-shot frequency domain holography diagnostic, the shape of these wakefields is captured for the first time. The wavefronts are observed to curve backwards, in contrast to the forwards curvature of wakefields in uniform plasma. Due to the expansion of the clusters, the first wakefield period is longer than those trailing it. The features of the data are well described by fully relativistic two-dimensional particle-in-cell simulations and by a quasianalytic solution for a one-dimensional, nonlinear wakefield in a cluster plasma.
Highlights
The frequency of electrons oscillating in a uniform plasma was first derived by Langmuir and Tonks in 1929 [1] and the behavior of Langmuir waves has been extensively studied [2,3,4,5,6]
Using an oblique angle single-shot frequency domain holography diagnostic, the shape of these wakefields is captured for the first time
Two widely studied applications of these waves are the beam-driven [7,8,9,10,11,12,13] and laser-driven [14,15,16] plasma accelerator, the latter using a high-power laser pulse propagating through a plasma to create longitudinal electric fields of up to 100 GV m−1 that accelerate charged particles
Summary
The frequency of electrons oscillating in a uniform plasma was first derived by Langmuir and Tonks in 1929 [1] and the behavior of Langmuir waves ( known as electron plasma waves) has been extensively studied [2,3,4,5,6]. Experimental data obtained from a single-shot, oblique-angle frequency-domain holography diagnostic [43] is presented, showing for the first time how the shape and wavelength of a wakefield are changed in the presence of clusters. These findings are supported by 2D particle-in-cell simulations which show that the wakefield wavelength decreases with increasing distance behind the drive pulse, in agreement with the experimental data. Controlling the plasma wavelength could potentially help to increase the dephasing length [15], which is one of the major limiting factors of wakefield accelerators It is observed for the first time that the wavefronts are curved backwards, in contrast to those in a uniform plasma.
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