I am a plasma scientist working with fusion. Firstly I would like to point out not all fusions of nuclei take the same amount of energy. Secondly diprotons are unstable and do not fuse under normal conditions due to spin-spin interaction. Lastly most fusion reactions occur at much less energy. Lastly doubling the energy would simply, under normal circumstances, just kinetic energy of the resultant particle, however if the raised energy causes other conditions to be met and depending on the fusionable material you could have differing types of decay.
I hope this was of some assistance.