An electron lens introduces “differences” in the bunches of a particle beam. In the illustration, the perspective is looking down the beam pipe — down the path of the particle beam. Left: the particle bunch, represented as a uniformly blue circle, contains particles that all behave in the same way. Because the constituent particles follow the exact same trajectory, as the bunch makes its way along the beam path, it is susceptible to wild deviations from the path. Right: Treated by an electron lens, the particle bunch represented by red and blue contains particles that move slightly differently from one another. For example, those particles closer to the interior of the bunch move differently from those closer to the outside. This variegation helps confine the particle bunch to the more desirable straightforward path.