Abstract
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.
Highlights
The intense laser fields achievable with the current technology allow the generation of large-amplitude plasma wakefields with associated strong longitudinal electric fields in low-density plasmas
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
We show that small-scale density ripples in the background plasma are sufficient to cause the uncontrolledinjection of electrons
Summary
The intense laser fields achievable with the current technology allow the generation of large-amplitude plasma wakefields with associated strong longitudinal electric fields in low-density plasmas. We show that small-scale density ripples in the background plasma are sufficient to cause the uncontrolled (self-)injection of electrons.
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