For overcoming the Coulomb barrier for fusion, methods other than heating the fusible material have been suggested. For example, if you were to use two particle accelerators to accelerate two beams of deuterons directly toward each other so as to collide head-on,
(a) What voltage would each accelerator require in order for the colliding deuterons to overcome the Coulomb barrier?
(b) Why do you suppose this method is not presently used?