 At 0.675 MeV, this process slows the proton to sub-keV energies in about 10−4 cm, many orders of magnitude less than what is required.Things can be improved somewhat by using two accelerators firing at each other instead of a single accelerator and a non-moving target.In this case, the second fuel, boron in the example above, is already ionized, so the "ionization drag" seen by the protons entering the solid block is eliminated.