A method and apparatus for producing heat is disclosed. The method involves the steps of accelerating one or more first particle(s) to a first velocity; colliding the accelerated particle(s) with one or more second particles in a collision zone located within a housing causing the first particle(s) and second particle(s) to form one or more collision mass(es) containing subatomic particles of the first and second particles; controlling the position of the collision mass(es) with electric and/or magnetic fields; and introducing one or more further particle(s) into the collision mass(es), the further particle(s) undergoing nuclear fusion with the one or more particles in the collision mass(es) producing fusion products and releasing heat.