Conceptual Design Reports

CDR chapter 8 - Photon Beam Transport and Diagnostics

FERMI@Elettra includes two separate undulator sections named FEL-1 and FEL-2 delivering radiation in the 100 ÷ 40 nm and 40 ÷ 10 nm ranges, respectively. For FEL-1 a 50 ÷ 100 fs pulse is delivered with a peak power of about 1-5 GW, and ~ 1014 photons per pulse are expected. FEL-2 is characterized by a 200 fs pulse carrying about 1 GW and 1012 (fresh bunch mode). In order to characterize, select, and carry the photon beam to the experimental endstations, a set of optical systems is placed after the undulators. Characteristics such as energy, energy resolution, pulse length, intensity, arrival time, polarization, and so on, are determined by means of several diagnostics located between the undulators and the experimental hall. Gas-based systems such as absorbers and intensity monitors are mounted within window-less in-vacuum sections. The gases intercepting the radiation axis serve as natural absorbers reducing the overall photon flux. Additionally, the gas ionization signal gives information about the relative intensity of the beam. A system of slits removes unwanted off-axis radiation mainly coming from spontaneous emission. It also works as an angular collimator making possible spectral-angular filtering. At the entrance of the experimental hall radiation coming from each FEL impinges on a plane mirror used as a power absorbing element upstream of the more delicate elements along the beamlines. Moreover, this optical element is important from the radio-protection point of view. ... Retrieve pdf