High-Current, Relativistic Electron-Beam Transport in Metals and the Role of Magnetic Collimation

High-resolution coherent transition radiation (CTR) imaging diagnoses electrons accelerated in laser---solid interactions with intensities of ~10¹⁹ W/cm². The CTR images indicate electron-beam filamentation and annular propagation. The beam temperature and half-angle divergence are inferred to be ~1.4 MeV and ~16^∘, respectively. Three-dimensional hybrid-particle-in-cell code simulations reproduce the details of the CTR images assuming an initial half-angle divergence of ~56^∘. Self-generated resistive magnetic fields are responsible for the difference between the initial and measured divergence.