In chapter 4 we have seen that, without elaborate source enhancement as described in section 6.4, an energy gain of the subcritical array on the order of 100 can be anticipated. With a desired total thermal power of the ADSR around 1 GWth, one sees that beam powers around 10 MW are needed. This is an order of magnitude larger than beam powers delivered by present accelerators. It is, therefore, important to examine the feasibility of such high-intensity accelerators. Since this discussion requires some knowledge of accelerator physics we give an introduction to this subject in Appendix III. It is shown there that, in practice, linear accelerators and cyclotrons are the best choices available for obtaining high average intensities that are almost continuous. It is thus instructive to review the characteristics of the existing high-intensity Linacs and cyclotrons.