Wakefields in a Cluster Plasma

We report the first study of large amplitude Langmuir waves in a plasma of nanometer-scale clusters. The shape of these wakefields is captured by an oblique-angle frequency-domain holography diagnostic for the first time. The wavefronts are observed to curve backwards, in contrast to the forwards curvature of wakefields in uniform plasma. The first wakefield period is longer than those trailing it. Next, the experimental data is compared to fully relativistic 2D particle-in-cell simulations and a new injection mechanism is found. Our simulations indicate that this mechanism leads to a greater maximum momentum and energy spread compared to electrons trapped in the uniform case.

This work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014-2018 under Grant agreement no. 633053. This work has also been funded by EPSRC Grant Numbers EP/L000237/1 and EP/R029148/1, and by STFC Grant Numbers ST/M007375/1 and ST/P002048/1. This work was supported by the European Research Council (InPairs ERC-2015-AdG Grant No. 695088). The authors want to thank the Osiris consortium and the staff of the CLF at STFC RAL. This work used the ARCHER UK National Supercomputing Service and STFC's SCARF cluster.