The undulator source of the Phoenix beamlines produces a discrete spectrum of photons, ranging from 200 to 8000 eV in a very narrow cone of about 50 µrad.The higher energy limit is given by the Ni-coating of the mirrors and a grazing incidence angle of 0.40. The lower limit comes from the minimum gap of the undulator.
|Type||Elliptical APPLE II type|
|Period length||54 mm|
|Magnetic Gap||18 - 70 mm|
|Number of periods||32|
|Polarization|| Linear (-50 - 1850)
Circular (right to left)
|Operating Harmonics||1 - 31|
|Energy range||150 eV - 8000 eV|
The APPLE type II undulator with variable polarization consists of four rows of NdFeB permanent magnet block arrays. One period of 54 mm consists of 4 x 4 magnets. By changing the longitudinal position of two rows, a horizontal field component is introduced. A shift in the same direction causes a helical trajectory while a shift in opposite directions tilts the linear polarization plane. Thus, variable linearly as well as circularly polarized light can be used at Phoenix. The vertical gap between the upper and lower rows defines the photon energy. The plot below shows the calculated UE54 spectrum at a gap setting of 23.3 mm. At this gap value the first harmonic is at 250 eV.
The front end safety system consists of the first beam position monitor (BPM), followed by a synchrotron radiation shutter, a fast valve, a Bremsstrahlung stopper, a second BPM, a beam-defining aperture (0.5 x 0.3 mrad2), and horizontal and vertical primary slits. The radiation power leaving the front end is about 1 kW for the smallest gap settings.