Advanced Photon Source

An Office of Science National User Facility

Electromagnetic Variable Polarizing Undulator (EMVPU)

As a part of the upcoming APS Upgrade, a group of APS Users has requested an undulator that is capable of producing x-rays with a variety of polarizations, including left- and right-circular, and horizontal and vertical linear polarizations.The x-rays produced will be used for magnetic studies of materials.For such studies, lower-energy photons are needed.The requested photon energy range is 400 eV to 2000 eV.

The undulator also needs to be capable of rapid switching between left- and right-handed circular polarizations.The magnetic signals of interest are weak – 10^4 or 10^5 times weaker than the main signal – so lock-in detection becomes essential for adequate sensitivity to the magnetic part of the signal.A switching frequency of 10 Hz is requested; a frequency below ~5 Hz is too slow to be useful.

APS_1428594 EMVPU First Review