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

Aniculaesei, Constantin and Pathak, Vishwa Bandhu and Kim, Hyung Taek and Oh, Kyung Hwan and Yoo, Byung Ju and Brunetti, Enrico and Jang, Yong Ha and Hojbota, Calin Ioan and Shin, Jung Hun and Jeon, Jong Ho and Cho, Seongha and Cho, Myung Hoon and Sung, Jae Hee and Lee, Seong Ku and Hegelich, Björn Manuel and Nam, Chang Hee (2019) Electron energy increase in a laser wakefield accelerator using up-ramp plasma density profiles. Scientific Reports, 9 (1). 11249. ISSN 2045-2322

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    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.