In anime, energy weapons which fire a colored beam of light are generally called "beam guns." A similar use in American science-fiction and animation is sometimes jokingly referred to as "FX_Ray lasers" (FX is the show biz acronym for special effects). Beam guns can be poorly defined as generic energy weapons (like phasers) or very specifically and tightly defined (like the "mega particle" firing "mega beam cannons" in Gundam), which operate using the series' quintessential Minovsky particles, M-Physics being the drive behind all the superscience there.
The use of the term "beam gun" definitely predates its appearance in Mobile Suit Gundam.
Beam weapons typically take one of many forms: Beam guns, beam cannons and beam rifles depending on whether they're small or large fixed mounts (beam guns and beam cannons) or hand_held mechaweapons (beam rifles). "Beam guns" are typically energy weapons that in some way do not behave like classical lasers or particle beams - sub-cpropagation rates, off-axis visibility (especially in space) and visible barrel recoil are typical non-laser-like properties found in beam guns.
The beam former has two sections which are separately connected to the two sides of the cathode block such that the cathode block acts as a heat sink for the beam former, and a thermal gradient is not produced within the beam former that would produce warpage and movement of the beam former.
The beam former, which has essentially the same shape of the anode, is connected to one of the sides of the cathode block and insulated from the other of the sides of the cathode block by an insulator.
A beam former is located between the anode and the filament and is configured so that the filament is shielded from the anode and the electrons are constrained to pass beneath the beam former and toward the anode in a ribbon-like electron beam.