Electromagnet/permanent magnet helical undulator (EMPHU)
Introduction
The production of circularly polarized synchrotron radiation from insertion devices is an important topic in most of X-ray facilities. In particular, dichroism measurements require devices having short flipping time between left and right circular polarization. This can be achieved with electromagnet based magnetic structures. The ESRF has developped a novel fast switching linear/helical undulator for this purpose. The device is optimized for the production of circular light in the range of 1 keV to 15 keV. A general view of the device is shown on the picture below.
| Period | 80 mm |
| Length | 1.6 m |
| Minimum gap | 16 mm |
| Vertical field source | Electromagnet |
| Horizontal field source | Permanent magnet (Sm2Co17) |
| Peak field @ min. gap | 0.2 T Hor. & Vert. |
| Max. current in coil | 250 A |
| Min. flip time | 5.6 msec |
More details on the structure and magnetic field
Related publication
J. Chavanne, P. Elleaume, P. VanVaerenbergh, "A Novel Fast Switching Linear/Helical Undulator", proc. of the EPAC98 Conference, 22-26 June 1998, p.317-319.