An electron beam is a directed population of electrons with specified energy, current and spatial distribution. Electric fields accelerate or focus it, while magnetic fields bend trajectories through the Lorentz force.
In an electron microscope, the beam's interaction with a specimen produces signals carrying structural information. Its brightness, energy spread and angular spread matter independently of total current. A vacuum reduces collisions with background gas, and electron-electron repulsion can limit transport at high current. Treating it as a single trajectory omits this collective and statistical structure.
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