THE POOPO UNDULATOR FOR THE CLIO EXPERIMENT

A permanent magnet undulator has been developed at the CEA for the CLIO infrared free electron laser at Orsay. This undulator consists of two independent parts, of equal length (l = 0.96 m) and of period lambda-0 = 4 cm. The magnetic gap can be adjusted separately, and, moreover, the second can be tapered. This allows both the gain and the energy extraction to be optimized over a wide range of wavelengths. The realisation of the undulator consisted of several steps: mechanical construction, magnets sorting and magnetic field measurements with the associated computed trajectory and spontaneous emission spectrum for one electron through the field. In addition, two different beam diagnostics methods have been studied for insertion into the vacuum chamber of the undulator: a carbon wire (secondary emission) profile monitor, at each end of the undulator, and three optical transition radiation screens for the alignment of the electron and the optical beams respectively.