Controlling the Self-Injection Threshold in Laser Wakefield Accelerators

• Published in: Physical review letters Vol. 121; no. 15; p. 154801
• Main Authors: Kuschel, S, Schwab, M B, Yeung, M, Hollatz, D, Seidel, A, Ziegler, W, Sävert, A, Kaluza, M C, Zepf, M
• Format: Journal Article
• Language: English
• Published: United States 12.10.2018
• ISSN: 1079-7114
• DOI: 10.1103/PhysRevLett.121.154801

Controlling the parameters of a laser plasma accelerated electron beam is a topic of intense research with a particular focus placed on controlling the injection phase of electrons into the accelerating structure from the background plasma. An essential prerequisite for high-quality beams is dark-current free acceleration (i.e., no electrons accelerated beyond those deliberately injected). We show that small-scale density ripples in the background plasma are sufficient to cause the uncontrolled (self-)injection of electrons. Such ripples can be as short as ∼50  μm and can therefore not be resolved by standard interferometry. Background free injection with substantially improved beam characteristics (divergence and pointing) is demonstrated in a gas cell designed for a controlled gas flow. The results are supported by an analytical theory as well as 3D particle in cell simulations.