Electron Trapping from Interactions between Laser-Driven Relativistic Plasma Waves

Grigory Golovin, Wenchao Yan, Ji Luo, Colton Fruhling, Dan Haden, Baozhen Zhao, Cheng Liu, Min Chen, Shouyuan Chen, Ping Zhang, Sudeep Banerjee, and Donald Umstadter

Phys. Rev. Lett. 121, 104801 – Published 7 September 2018

Abstract

Interactions of large-amplitude relativistic plasma waves were investigated experimentally by propagating two synchronized ultraintense femtosecond laser pulses in plasma at oblique crossing angles to each other. The electrostatic and electromagnetic fields of the colliding waves acted to preaccelerate and trap electrons via previously predicted, but untested injection mechanisms of ponderomotive drift and wake-wake interference. High-quality energetic electron beams were produced, also revealing valuable new information about plasma-wave dynamics.

Received 15 December 2017

DOI:https://doi.org/10.1103/PhysRevLett.121.104801

Physics Subject Headings (PhySH)

Laser driven electron acceleration Laser wakefield acceleration Particle acceleration in plasmas Plasma-beam interactions

Plasma Physics

Authors & Affiliations

Grigory Golovin¹, Wenchao Yan¹, Ji Luo^2,3, Colton Fruhling¹, Dan Haden¹, Baozhen Zhao¹, Cheng Liu¹, Min Chen^2,3, Shouyuan Chen¹, Ping Zhang¹, Sudeep Banerjee¹, and Donald Umstadter^1,*

¹Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588, USA
²Key Laboratory for Laser Plasmas (Ministry of Education) and School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China
³Collaborative Innovation Center of IFSA (CICIFSA), Shanghai Jiao Tong University, Shanghai 200240, China

^*Corresponding author. donald.umstadter@unl.edu

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Issue

Vol. 121, Iss. 10 — 7 September 2018

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Images

Figure 1
Schematic of the experiment. By changing the delay between pulse arrival times, three scenarios resulted: (a) the drive pulse arrives at the intersection after the injector one and interacts with the injector wake. (b) Both pulses arrive at the intersection simultaneously. (c) The injector pulse arrives at the intersection after the drive one and interacts with the drive wake. The polarization of the laser pulses is horizontal (black arrows), with the directions indicated by red arrows.
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Figure 2
(a) Spectral profiles of magnetically dispersed $e$ beams and (b) corresponding spectral lineouts. The left panel of (a) and the black curve in (b) show the $e$ beam generated with the drive pulse only. The other beams were generated with both drive and injector pulses with no delay between them.
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Figure 3
Electron-beam properties vs delay between the drive and injector laser pulses. (a) Course time scan ( $n_{e} = 1.0 \times 10^{19} {cm}^{- 3}$ , plasma period $τ_{p} = 35 fs$ ). Each point shows 3.4 shots on average; the error bars show standard deviations. The green line shows results of PIC simulations. Purple area shows charge measured with the drive pulse only ( $\pm 1$ standard deviation). b) Fine time scan ( $n_{e} = 7.6 \times 10^{18} {cm}^{- 3}$ , $τ_{p} = 40 fs$ ). Each point shows 10 shots on average. Light blue area represents standard deviation of the data, dark blue area—standard error of the mean. The red dashed lines show data fits with (a) bi-Gaussian function (red numbers show half widths at half maximum calculated from the fit); (b) sums of sine and linear functions (red number shows a period of the plasma wave, calculated from the fit).
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Figure 4
Results of PIC simulations for electron injection into the drive wake in the cases when the injector pulse arrives at the intersection before the driver pulse (a), at the same time (b), or after the driver pulse (c). The white-blue-black (horizontal) color bar represents background plasma density, the red-green-black (vertical) color bar—electric field. The black points are the initial positions of typical injected electrons. The color curves show typical trajectories of those electrons. The figures at the bottom of each panel show the same trajectories with “o” marking their starting points. Labels are drive pulse (Dr), injector pulse (Inj), drive wake ( ${Dr}_{w}$ ), and injector wake ( ${Inj}_{w}$ ), respectively, and point to the locations along electron trajectories experiencing the field of each.
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