Electron energy increase in a laser wakefield accelerator using up-ramp plasma density profiles

Constantin Aniculaesei,Kyung Hwan Oh,Byung Ju Yoo,Seongha Cho,Seong Ku Lee,Calin Ioan Hojbota,Hyung Taek Kim,Björn Manuel Hegelich,Vishwa Bandhu Pathak,Chang Hee Nam,Jae Hee Sung,Jung Hun Shin,Myung Hoon Cho,Jong Ho Jeon,Yong Ha Jang,Enrico Brunetti

doi:10.1038/s41598-019-47677-5

Abstract

The phase velocity of the wakefield of a laser wakefield accelerator can, theoretically, be manipulated by shaping the longitudinal plasma density profile, thus controlling the parameters of the generated electron beam. We present an experimental method where using a series of shaped longitudinal plasma density profiles we increased the mean electron peak energy more than 50%, from 175 ± 1 MeV to 262 ± 10 MeV and the maximum peak energy from 182 MeV to 363 MeV. The divergence follows closely the change of mean energy and decreases from 58.9 ± 0.45 mrad to 12.6 ± 1.2 mrad along the horizontal axis and from 35 ± 0.3 mrad to 8.3 ± 0.69 mrad along the vertical axis. Particle-in-cell simulations show that a ramp in a plasma density profile can affect the evolution of the wakefield, thus qualitatively confirming the experimental results. The presented method can increase the electron energy for a fixed laser power and at the same time offer an energy tunable source of electrons.

Highlights

The phase velocity of the wakefield of a laser wakefield accelerator can, theoretically, be manipulated by shaping the longitudinal plasma density profile, controlling the parameters of the generated electron beam
We present an experimental method where using a series of shaped longitudinal plasma density profiles we increased the mean electron peak energy more than 50%, from 175 ± 1 MeV to 262 ± 10 MeV and the maximum peak energy from 182 MeV to 363 MeV
In order to experimentally investigate the influence of the phase-locking mechanism on the performance of an laser wakefield accelerator (LWFA), an experiment has been performed at the Center for Relativistic Laser Science, Institute for Basic Science (IBS), Republic of Korea

Summary

Introduction

The phase velocity of the wakefield of a laser wakefield accelerator can, theoretically, be manipulated by shaping the longitudinal plasma density profile, controlling the parameters of the generated electron beam. As the laser pulse passes, the background electrons are attracted by the local space-charge field and start to oscillate around the ions at the plasma frequency setting up a plasma wave trailing behind the laser pulse This kind of wave is called a wakefield and constitutes the essential part of a laser wakefield accelerator (LWFA)[3]. In the frame of reference of the electron bunch, in these conditions, the back of the bubble is stationary This process is called phase-locking and it has been theoretically shown[18,19,20,21,22,23,24] that it can control the parameters of the electron beam such as energy and emittance/divergence

Methods

Results

Conclusion