During recent years several attempts have been undertaken to decrease
the period length of undulators to the millimetre range. Zn this paper
a novel type of in-vacuum undulator is described which is built using
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 teste
d with a beam in the near future.