SMALL-GAP UNDULATOR RESEARCH AT THE NSLS - CONCEPTS AND RESULTS

We report the results of experiments carried out in the X13 straight s ection of the NSLS X-ray Ring, which explore the limits of operation o f small-gap undulators. Two major projects are described: the Prototyp e Small-Gap Undulator (PSGU) and the In-Vacuum UNdulator (IVUN). The P SGU utilized a variable-aperture vacuum chamber and a separate drive f or the 16-mm-period undulator magnet arrays, which were situated in ai r outside the vacuum vessel. For IVUN, the 11-mm-period undulator arra ys were placed directly in the accelerator vacuum. For both devices, s tored beam lifetimes in the X-ray Ring were unaffected until electron beam apertures were decreased below 5 mm. A 3 mm aperture resulted in only a slight reduction of beam lifetime, which is acceptable for norm al user operations. Measurements of the photon spectra radiated by the PSGU and IVUN were in excellent agreement with theory. Our work provi des strong evidence that small-gap, short-period undulators will play an important role in the future. (C) 1998 Elsevier Science B.V. All ri ghts reserved.