Dynamics of ionization-induced electron injection in the high density regime of laser wakefield acceleration

• DOI: 10.1063/1.4903845
• Publication Date: 2014-12-08T18:00:35Z
• Authors: F. G. Desforges; B. S. Paradkar; M. Hansson; J. Ju; L. Senje; T. L. Audet; A. Persson; S. Dobosz-Dufrénoy; O. Lundh; G. Maynard; P. Monot; J.-L. Vay; C.-G. Wahlström; B. Cros
• Keywords: [PHYS.PHYS]Physics [physics]/Physics [physics]; 0103 physical sciences; 01 natural sciences; 7. Clean energy

The dynamics of ionization-induced electron injection in high density (∼1.2 × 1019 cm−3) regime of laser wakefield acceleration is investigated by analyzing the betatron X-ray emission. In such high density operation, the laser normalized vector potential exceeds the injection-thresholds of both ionization-injection and self-injection due to self-focusing. In this regime, direct experimental evidence of early on-set of ionization-induced injection into the plasma wave is given by mapping the X-ray emission zone inside the plasma. Particle-In-Cell simulations show that this early on-set of ionization-induced injection, due to its lower trapping threshold, suppresses the trapping of self-injected electrons. A comparative study of the electron and X-ray properties is performed for both self-injection and ionization-induced injection. An increase of X-ray fluence by at least a factor of two is observed in the case of ionization-induced injection due to increased trapped charge compared to self-injection mechanism.