Fusion Turrets were defense 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 would pop out from the ground. Their strength and armor was strong and they could attack up to long range. These machines would pop out from the ground whenever someone was close by, and then would shoot at them.
The best weapons for these machines were long range weapons or Plasma Beasts, as they could attack without Ratchet being vulnerable turret fire.
Ratchet & Clank Future: A Crack in TimeIn A Crack in Time, a fusion turret was used during one challenge at the Agorian Battleplex, Fun With Fusion Turrets.
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.