  Short period, high field undulators are used to produce hard X-rays on
synchrotron radiation based storage ring facilities of intermediate energy and
enable short wavelength Free Electron Laser. Cryogenic permanent magnet
undulators take benefit from improved magnetic properties of RE2Fe14B (Rare
Earth based magnets) at low temperatures for achieving short period, high
magnetic field and high coercivity. Using Pr2Fe14B instead of Nd2Fe14B, which
is generally employed for undulators, avoids the limitation caused by the Spin
Reorientation Transition phenomenon, and simplifies the cooling system by
allowing the working temperature of the undulator to be directly at the liquid
nitrogen one (77 K). We describe here the development of a full scale (2 m), 18
mm period Pr2Fe14B cryogenic permanent magnet undulator (U18). The design,
construction and optimization, as well as magnetic measurements and shimming at
low temperature are presented. The commissioning and operation of the undulator
with the electron beam and spectrum measurement using the Nanoscopmium beamline
at SOLEIL are also reported.
