An electron beam can be compared to the light from a laser pointer: if it diverges, the spot on the wall quickly spreads out. In the lab, physicists created such a narrow beam that it remained thin over a long distance, like the beam of a good pointer. To do this, they accelerated electrons in a plasma accelerator, where particles are caught up in a wave in ionized gas, and then compressed the stream with a permanent magnet solenoid.
The beam's thickness was measured: it turned out to be just 124 nanometers per radian of divergence. That's like a flashlight beam expanding less than the width of a human hair after traveling a kilometer. This neat beam was directed at an ultra-thin silicon film, and a clear diffraction pattern appeared on the detector — a pattern of bright spots that reveals how atoms are arranged in the crystal.
The main achievement is that a compact setup produces a beam as good as the bulky radio-frequency accelerators typically used for electron diffraction. This paves the way for tabletop instruments for materials research: you could examine the structure of proteins, semiconductors, or new alloys right in a small lab, without waiting for time on a huge accelerator.
Electrons in such a beam travel at nearly the speed of light, but because of their tiny mass, they can be deflected by a magnet the size of your palm.