In the past, variable energy particle accelerators have, in general, been limited to the energy range below about 4 MeV. Many fixed energy machines have been built to operate above this energy but the field of physical research made possible by a variable energy machine between 2 and 12 MeV has been largely neglected. With particles of energy above about 10 MeV some energy variation may be achieved with absorbing foils, but this technique is unsatisfactory at lower energies.