Fusion Turrets were defence turrets that were used all across the Polaris Galaxy.
Ratchet & Clank Future: Tools of Destruction
In Tools of Destruction, the turrets were posed as enemies that popped out from the ground. Their strength and armor was strong and they could attack up to long range. These machines popped out from the ground when someone was close by, and then shot at them.
Fusion Turrets were first encountered by Ratchet in the Nundac Asteroid Ring.
Ratchet & Clank: All 4 One
In All 4 One, they could be found as security measures installed on the roof of Zogg Tower by Artemis Zogg, in case of an attack by Nefarious on Luminopolis. They were used to destroy a Lumenoid power source adjacent to the tower before the Light Eating Z'Grute could harvest any more light energy.