Abstract: An S-band standing wave electron accelerator structure having a multiplicity of resonant accelerating cavities and resonant coupling cavities mounted sequentially in an alternating accelerating cavity-coupling cavity pattern along an accelerator axis, with adjacent cavities separated by a common wall. The common walls and end walls of the structure have beam holes concentric with the axis, and the common walls further have two slots for coupling energy between the cavities. To prevent direct coupling between the accelerating cavities which are separated by a coupling cavity, the coupling slots in one wall of the coupling cavity are rotated approximately 90.degree. about the accelerator axis with respect to the coupling slos in the other wall. The structure is assembled by brazing a number of conductive segments together. Each segment forms half of each of the adjacent cavities having the common wall and thus consists of half of an accelerating cavity and half of a coupling cavity.