During the last years several attempts were undertaken to decrease the period length of undulators to the mm range. In this paper, a novel type of an in-vacuum undulator is described which is built with superconductive wires. The period length of this special device is 3.8 mm. In principle, it is possible to decrease this period length even further. A 100 period long undulator has been built and will be tested with beam in the near future.
@article{arxiv.physics/9711018,
title = {A superconductive undulator with period length of 3.8 mm},
author = {T. Hezel and B. Krevet and H. O. Moser and J. A. Rossmanith and R. Rossmanith and Th. Schneider},
journal= {arXiv preprint arXiv:physics/9711018},
year = {2009}
}