INCREASED X-RAY-PRODUCTION EFFICIENCY FROM TRANSITION RADIATORS UTILIZING A MULTIPLE-PASS ELECTRON-BEAM

We have observed x-ray emission from transition radiators placed insid e an electron storage ring. The radiators were thin (0.18-9 mu m) and the electrons were of sufficient energy (118-252 MeV) so that the elec trons passed through the radiators many times. This effectively increa sed the efficiency of the radiators (photons/electron). The electron-b eam lifetime in the storage ring was measured, and used to determine t he number of passes through each radiator. Multiple passes between 5 a nd 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 out put power and the spatial distribution of the x rays were measured. Th e emission pattern was the typical annular cone of transition radiatio n. Single-foil transition radiation was observed whose total output po wer 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. (C) 1998 Am erican Institute of Physics. [S0034-6748(98)01606-2].