Thermal wakefield structure in plasma acceleration processes: insights from fluid models and PIC simulations

We focus on the process of plasma acceleration in the presence of non-negligible thermal effects, wherein a driver of relativistic electrons perturbs a warm neutral plasma and generates a wakefield structure. We study the acceleration process via numerical simulations based on fluid models with different thermal closure assumptions, and also provide systematic comparisons against ground-truth data coming from particle-in-cell (PIC) simulations. The focus of the analysis is on the first electron depletion bubble after the driver, where we provide a detailed characterization of its size and the electromagnetic fields developed inside. Our results are instrumental in determining the correct thermal closure assumption to be used in fluid models for the numerical simulations of plasma acceleration processes, as well as elucidating the corresponding limits of applicability.