Figure 1. The diffraction apparatus includes an rf trap, Faraday cup, and microchannel plate detector (MCP), and is structured to maintain a cylindrical symmetry around the electron-beam axis. The e beam passes through a trapped ion cloud producing scattered electrons, indicated by dashed lines. The primary beam enters the Faraday cup and scattered electrons strike an image quality MCP, producing a diffraction pattern on a phosphor screen. This screen is imaged by a scientific-grade CCD camera mounted external to the UHV chamber. The distance from the trapped ion cloud to the MCP is approximately 7.5 cm in these experiments. The channeltron electron multiplier detects ions ejected from the trap after a diffraction exposure.