Benchmarking a high-order particle-in-cell code for the simulation of a gyrotron traveling-wave tubeP. Ortwein, S.M. Copplestone, C.-D. Munz, A. Marek and J. JelonnekEPJ Web Conf., 149 (2017) 04020DOI: https://doi.org/10.1051/epjconf/201714904020