Double tapered IFEL undulator
Data from Hall probe scan on the undulator axis
Double tapered IFEL undulator
Data from Hall probe scan on the undulator axis
The undulator has been designed and built in collaboration with the Kurchatov Institute of Moscow.
The requirements for the Neptune IFEL undulator were:
1. Transparency for both the electron and the laser beams.
2. Synchronism between the electron and the laser wave along the whole undulator length, including the focus region, where the Guoy phase shift takes place.
3. Maximize acceleration rate and energy gain at the exit.
4. Maximize capture fraction and electron beam trapping
5. Small sensitivity to possible transverse displacements of the laser focus (jitter).
To provide the transparency the undulator gap is made large, 12 mm. To fullfill the other requirements a double tapering of both the magnetic field strength and the undulator periods is used.
| Initial | Final | |
| Period | 1.5 cm | 5.0 cm |
| Magnetic field | 0.1 T | 0.6 T |
| K | 0.2 | 2.8 |
| gap | 12 mm | 12 mm |
| Resonant electron energy | 14.5 MeV | 53 MeV |
The magnetic field profile is given in the figure.
The data is obtained with an Hall Probe scan through the undulator axis. The precision and accuracy of the magnetic field measurements are less than 0.01%.
[1] A.A. Varfolomeev et al., ``An undulator with non-adiabatic tapering for the IFEL project'' NIM 483 377 (2002)