The DSR Linac is a patented linear accelerator suitable for boosting the energy of electrons traveling near the speed of light (v/c ~ 1). Adjacent accelerating cavities are coupled using compact resonant slots, rather than bulky off-axis cavities used in side-coupled linacs. Similar to side-coupled linacs, the accelerating mode is electrically a π/2 mode, where the resonant slots are not excited, while the particles experience an on-axis accelerating field resembling a π mode. The cell-to-cell coupling of the DSR Linac is greater than that of a side-coupled cavity, resulting in greater separation between the accelerating mode and the nearest mode on either side. The replacement of bulky side cavities by resonant slots reduced the radial size of the DSR Linac, reducing the clear aperture requirement of any magnetic focusing elements.