A planetary ion cannon was a massive blaster weapon that could be used to temporarily or permanently disable electrical systems and penetrate shields. Used mainly in defense, they were also used by pirates on anarchic worlds such as Lok to disable ships for looting.
Its power source was usually a dedicated reactor sunken into the ground and it could be erected in several hours.
One was seen on the planet of Hoth during the Battle of Hoth. The ion cannon fired at an Imperial-Star Destroyer leaving it non-operational, thus letting some Rebel medium transports escape the planet before the Imperial invasion commenced.