The undulators of the ELBE FELs

At the ELBE facility two permanent magnet undulators are installed producing light in the mid and far infrared region.
  • The undulator U27, which consists of 2 separate units, can be tuned from 3.5 μm to approximately 22 μm.
  • The U100 undulator extends the wavelength range up to about 280 μm.

Table 1:
The main parameters of the ELBE undulators. The undulators are labelled UλU according to the length λU (in mm) of their magnetic periods.

  
Parameter Undulator
  U27 U100
Undulator period λU 2.73 cm 10 cm
Number of periods NU 2*34 38
Undulator parameter Krms 0.3 - 0.7 0.5 - 2.7

The wavelength of the produced light is determined by the energy of the electron beam and by the magnetic undulator field. The latter is characterized by the undulator parameter Krms which is determined by the number NU of undulator periods and by the length  λU of a period according to

Krms = eBUrms λ U / (2π mc) ≈ 0.934 BUrms[T] λU[cm],    (1)

where BUrms is the rms field amplitude on the undulator axis. (m: electron rest mass, -e: electron charge, c: vacuum velocity of light)

Control measurements of the undulator fields of U27 have been performed using the pulsed-wire method.