# 17th Advanced Accelerator Concepts Workshop

31 July 2016 to 5 August 2016
Gaylord Hotel and Conference Center
US/Eastern timezone

## Interaction Between Laser Pulses and Trailing Wakefields Intersecting at Small Angle for LWFA Charge Yield Enhancement

1 Aug 2016, 15:50
20m
Woodrow Wilson CD (Gaylord Hotel)

### Woodrow Wilson CD

#### Gaylord Hotel

Oral Working Group 1

### Speaker

Kathleen Weichman (University of Texas at Austin)

### Abstract

Increasing the high energy electron yield from laser wakefield acceleration is crucial to its development as an electron beam source. We present a scheme for charge yield enhancement using two equal-intensity pulses colliding at small angle. VORPAL particle-in-cell simulations show the relative phase between pulses controls their separation and the stability of the combined structure. Pi phase shift produces density structure merging, bringing the pulses closer together relative to zero phase shift.

### Summary

In laser wakefield acceleration (LWFA), a laser pulse drives a plasma wake capable of trapping and accelerating electrons. Previous studies of LWFA charge yield enhancement using two colliding pulses have concentrated on counterpropagating, transverse, or collinear geometry with one strong pulse driving the wake and another, weaker pulse facilitating electron trapping. In 2013, Yang, et al. [1] proposed a scheme involving nearly copropagating pulses with mutually perpendicular polarization and roughly equal intensity colliding at an angle around $5^\circ$, resulting in higher charge yield via the merging of initially separate plasma bubbles. However, the merged bubble was unstable and yielded lower maximum electron energy and larger angular divergence than the single pulse case. Here we consider pulses with mutually parallel polarization intersecting at smaller angles ($<1^\circ$) in lower density ($\sim 10^{17}$ cm$^{-3}$) plasma to enable interaction of pulses and their wakes over centimeter-scale propagation distances. VORPAL [2] particle-in-cell simulations indicate that stability of the combined two (or more) bubble structure depends on the relative phase between laser pulses. Destructive interference along the propagation axis produces unstable density structures which merge with the original laser-driven wakes, decreasing the pulse separation and producing wakefields in which the driving laser intensity is not cylindrically symmetric. 2D and 3D simulations will be presented to illustrate conditions for stability, high charge yield, and good peak electron energy. This work is supported by the DOE under Grants No. DE-SC0011617 and DE-SC0012444, by DOE/NSF Grant No. DE-SC0012584, and used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. KW is supported by the DOE CSGF under Grant No. DE-FG02-97ER25308.

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### Primary author

Kathleen Weichman (University of Texas at Austin)

### Co-authors

Adam Higuera (University of Colorado Boulder, Tech-X Corporation) Dr. Benjamin Cowan (Tech-X Corporation) Dr. Dan Abell (Tech-X Corporation) Dr. John Cary (Tech-X Corporation, University of Colorado Boulder) Dr. Michael Downer (University of Texas at Austin) Dr. Neil Fazel (University of Texas at Austin)

### Presentation Materials

 Weichman_AAC_16.pptx Weichman_AAC.zip
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