The annular confinement beam, or ACB for short, is an essential component of the Star Trek transporter system.  This integrated component of the transporter's energizing coils creates a spatial matrix which ensures a transport object is confined to the necessary beam radius targeted by the molecular imaging scanners. This is essential in order for the subject to be safely dematerialized into a subatomic debonded matter stream. Generated by the primary energizing coils, the ACB confines the transporter matter stream when it is on its way to the target destination.

Annular beam confinment is an actual technique used in physics to produce 'bunched' annular electron beams in high-power microwave (HPM) sources, such as relativistic klystron amplifiers, relativistic klystron oscillators (RKO), and backward wave oscillators (BWO). A klystron is a specialized linear-beam vacuum tube that is used to amplify microwave and radio frequencies and high-power carrier waves for communications  and modern particle accelerators. A backward wave oscillator (BWO), also called carcinotron is a vacuum tube that is used to generate microwaves up to the terahertz range and is used for a variety of military applications such as radar jamming and tracking airborne targets.

Two-cavity klystron