Increased x-ray production efficiency from transition radiators utilizing a multiple-pass electron beam

We have observed x-ray emission from transition radiators placed inside an electron storage ring. The radiators were thin (0.18-9 μm) and the electrons were of sufficient energy (118-252 MeV) so that the electrons passed through the radiators many times. This effectively increased the efficiency of the radiators (photons/electron). The electron-beam lifetime in the storage ring was measured, and used to determine the number of passes through each radiator. Multiple passes between 5 and 385 were observed, thus giving a corresponding increase in radiator efficiency. Five electron-beam energies (118, 151, 181, 213, and 252 MeV) were used on a variety of radiators consisting of both single and multiple foils and different materials (C, Al, Cu, Ta). The total output power and the spatial distribution of the x rays were measured. The emission pattern was the typical annular cone of transition radiation. Single-foil transition radiation was observed whose total output power was comparable to that of multiple-foil radiators composed of the same material. Thus, for this range of parameters, the product of the number of foils times the number of passes was a constant.