From Teletraan I: The Transformers Wiki

Plasma cannons are weapons which fire bursts of plasma at opponents.

[edit] Fiction

[edit] Beast Wars

The Axalon was equipped with a plasma cannon. When it became apparent that the ship was falling into an unnamed planet's atmosphere, Optimus Primal ordered that the plasma cannon be fired on the fleeing Darksyde. The blast successfully crippled the Predacon vessel. Beast Wars (Part 1)

[edit] Movie continuity

Plasma cannons are employed by both the Autobots and the Decepticons. Ghosts of Yesterday

Upon arriving on Earth, Starscream used his plasma cannon to destroy an F-22 Raptor that he had just scanned. Prime Directives issue 4

Bumblebee's primary weapon was a plasma cannon, which he used to great effect against Devastator...as well as intimidating his former Sector Seven oppressors. Transformers