Stable, tunable, quasimonoenergetic electron beams produced in a laser wakefield near the threshold for self-injection

• Main Authors: S. Banerjee, S. Y. Kalmykov, N. D. Powers, G. Golovin, V. Ramanathan, N. J. Cunningham, K. J. Brown, S. Chen, I. Ghebregziabher, B. A. Shadwick, D. P. Umstadter, B. M. Cowan, D. L. Bruhwiler, A. Beck, E. Lefebvre
• Format: Article
• Language: English
• Published: American Physical Society 2013-03-01
• Series: Physical Review Special Topics. Accelerators and Beams
• Online Access: http://doi.org/10.1103/PhysRevSTAB.16.031302

Stable operation of a laser-plasma accelerator near the threshold for electron self-injection in the blowout regime has been demonstrated with 25–60 TW, 30 fs laser pulses focused into a 3–4 millimeter length gas jet. Nearly Gaussian shape and high nanosecond contrast of the focused pulse appear to be critically important for controllable, tunable generation of 250–430 MeV electron bunches with a low-energy spread, ∼10  pC charge, a few-mrad divergence and pointing stability, and a vanishingly small low-energy background. The physical nature of the near-threshold behavior is examined using three-dimensional particle-in-cell simulations. Simulations indicate that properly locating the nonlinear focus of the laser pulse within the plasma suppresses continuous injection, thus reducing the low-energy tail of the electron beam.