A proton cannon was a weapon used by several races, including the Daleks.
A mixture of potatoes, turnips and molasses were once used by the Tenth Doctor to clog up proton cannons being fired upon him and Martha Jones. Having landed aboard an American schooner in the Caribbean Sea during the Quasi-War, the time travellers had to quickly prepare the mixture to thwart their attackers. The mixture gunked up the cannon's intake valve and immediately caused it to explode. (COMIC: Second Wave)
A group of Daleks unleashed their proton cannon on 22nd century Earth, resulting in all life becoming intangible (unable to touch solids). The plan was that, unable to eat, humans would soon just waste away from the Earth and the Dalek survivors would rebuild war ships and attack. However, the Tenth Doctor used the Krikoosh to enter the building and reach the proton cannon. Unhurt by the Daleks' rays, the Doctor made some adjustments and turned the weapon against the Daleks. The humans became solid again and the Daleks with their "protective" shield were now the intangible ones. The Daleks judged this an unacceptable outcome and initiated self-destruct. (COMIC: Extermination of the Daleks)