Trapping of High-Current Relativistic Electron Beams in a Magnetic Mirror Trap

500-keV, 10-kA electron beams are injected into a magnetic mirror trap of Astron geometry without wall resistors. When using ${\mathrm{H}}_2$ and pressures of several hundred millitorr in the tank, we observe ring-shaped electron layers exhibiting field changes $\rho =\frac{\delta B}{B_{\mathrm{vac}}}$ of up to 120% in the trap center and lifetimes of up to 20 μsec. With the exception of a fast final "dump" when the $\rho$ of the layer has decreased to small values, we observe a smooth decay of the layer, roughly compatible with scattering of the fast electrons in the background gas.